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Valid Sat May 18, 2024
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NWS Weather Prediction Center College Park MD
350 PM EDT Thu May 16 2024
Valid 00Z Fri May 17 2024 - 00Z Sun May 19 2024
...Dangerous and life-threatening flash flooding likely today for portions
of eastern Texas and western Louisiana...
...Potentially significant heavy rainfall threat spreads into portions of
southern Mississippi and western Alabama tomorrow...
...Sweltering heat continues across South Florida and South Texas into
this weekend...
The main weather story today remains the dangerous and life-threatening
flash flood potential over the Lower Mississippi Valley into the overnight
hours as widespread thunderstorms batter areas which are very vulnerable
to additional rainfall. Since the upgrade to a High Risk (level 4/4) of
Excessive Rainfall last night, little has changed this afternoon regarding
the placement and severity of the flash flooding threat in eastern Texas
and western Louisiana. Radar across east-central Texas this afternoon
depicts an expansive thunderstorm complex growing along a warm front, with
very moist and unstable air feeding into it to support continuous storm
development this afternoon. Going into the evening and overnight hours,
repeating of these thunderstorms containing very heavy rainfall rates
within the complex will lead to rainfall amounts of 5-8" today within the
High Risk area over eastern Texas and western Louisiana before the
thunderstorms migrate eastward by tomorrow morning. Remember, High Risks
for Excessive Rainfall are a BIG DEAL: 1/3 flood related fatalities and
4/5 flood related damages occur in WPC High Risks, so pay attention to the
latest warning information and NEVER drive or walk into floodwaters.
Flooding aside, the same storms are also capable of producing a few
tornadoes, severe wind, and hail, with the Storm Prediction Center
maintaining an Enhanced Risk (level 3/5) of severe weather over much of
the same area today.
By tomorrow morning, the threat of significant flash flooding will spread
east into southern Mississippi and western Alabama as the aforementioned
warm front stalls out over the Southeast. Once again, a very moist and
unstable atmosphere appears primed to support bouts of prolific heavy
rainfall, with multiple rounds of storms expected as multiple disturbances
aloft traverse the area. When combined with saturated soils from recent
heavy rainfall, a Moderate Risk (level 3/4) is in effect tomorrow with
areal rainfall amounts upwards of 2-5" (locally up to 7") possible. It
should be noted that there is some uncertainty with where the heaviest
rain falls owing to how the current storms in Texas behave later today, so
stay tuned for any adjustments to the forecast. Once again, severe weather
will also be an issue south of the warm front across the Gulf States, with
a Slight Risk (level 2/5) in effect for few tornadoes, very large hail,
and damaging wind.
The same warm front driving the thunderstorms will also contribute to
sweltering heat in South Florida and Texas. Recent experimental NWS
HeatRisk guidance continues to suggest moderate to locally major heat
related impacts will continue across these areas at least through Saturday
due to the combination of heat indices eclipsing 100 degrees, with little
overnight relief expected.
Asherman
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
NWS Weather Prediction Center College Park MD
258 PM EDT Thu May 16 2024
Valid 12Z Sun May 19 2024 - 12Z Thu May 23 2024
...Overview...
Reasonably agreeable model guidance indicates that an upper trough
and surface low should move out of the eastern U.S. but linger in
the western Atlantic through the first half of next week.
Meanwhile, mean troughing will develop in the western U.S., which
along with frontal boundaries should help develop some locally
heavy convection across north-central parts of the Plains and
Mississippi Valley toward the Great Lakes region early to midweek.
Leading shortwave energy looks to push across the northern two-
thirds of the U.S. along with a cold front Tuesday-Thursday, while
an upper low drops south into the Northwest. Cool conditions with
increasing precipitation chances are forecast for the Northwest,
including higher elevation snow.
...Guidance/Predictability Assessment...
Recent model guidance is generally agreeable with the overall
pattern, with some typical detail uncertainties. There is still
some spread with the specifics of the eastern U.S. to western
Atlantic low, but the 00Z UKMET seemed to be the main outlier with
it in showing a farther east/progressive solution more reminiscent
of models from a couple days ago, so a GFS/ECMWF/CMC blend worked
well. Farther west, models indicate a few features of note that
combine into the western U.S. trough. A small southern stream
eastern Pacific closed low Sunday will track eastward and get
absorbed likely Monday-Tuesday, while northern stream energy pivots
through the northwestern and north-central U.S. within the trough.
00Z/06Z model guidance seemed agreeable with that but the new 12Z
CMC now lingers that energy in the West longer while other models
progress it into the Midwest. The new 12Z CMC also seems like an
outlier upstream as it does not show the upper low dropping south
through the western side of the trough by midweek.
The WPC forecast used a blend of the 00/06Z GFS and 00Z ECMWF and
CMC runs early in the period, with gradually increasing
incorporation of ensemble means to about half by the end of the
period. This maintained good continuity with the previous forecast.
...Weather/Hazards Highlights...
During the Sunday-Monday night time frame covered by the Days 4-5
Excessive Rainfall Outlooks, the primary region of interest will
extend from the central Plains into the Midwest. A Plains surface
low should lift an initially stalling front northward as a warm
front while a wavy boundary should hang up for a time over the
Plains/Upper Midwest early next week while awaiting the approach of
western U.S. dynamics. There is still some scatter for details of
the placement for possibly multiple rounds of thunderstorms in this
area, but the ingredients of ample moisture/instability and lift
warrant continuing Marginal Risks in the EROs for both Days 4 and
5, with threats on Day 5 depending somewhat on how Day 4
transpires. From early Tuesday onward, expect northeastward
progression of developing low pressure to push the trailing cold
front and accompanying rain and thunderstorms of varying intensity
farther east and south. Rainfall amounts could be heavy across the
Midwest into the Great Lakes region, but other than that it will
take additional time to resolve most favored areas of heaviest
rainfall in the eastern and southern U.S. for the Tuesday-Thursday
time frame.
Aside from the north-central U.S., there is some concern Sunday
for locally heavy rain in the Southeast to southern Mid-Atlantic
with the departing low pressure system, but without enough of a
signal to warrant a risk area. Then in the West, initial upper
troughing will support some precipitation over northern areas with
scattered activity possibly reaching as far south as the Great
Basin. Some snow will be possible in the high elevations of the
Rockies, along with high winds possible on Sunday. Approach/arrival
of another upper low as currently advertised by midweek or so
would produce somewhat more organized precipitation at that time.
Changes in snow levels will depend on the depth of the upper low.
Expect South Texas to see multiple days of hazardous heat during
the period with highs persistently running 10-15F above normal with
max heat index values possibly reaching at least 110F. Highs near
or over 100 degrees could stretch farther north across the southern
High Plains at times. Some daily records for highs/warm lows will
be possible. Southern Florida may also experience hazardous heat
into Sunday with highs locally up to 5-10F above normal and max
heat index values reaching 105-110F, followed by continued above
normal but slightly less extreme readings.
The forecast pattern will favor below average highs over the
Northwest for most of next week, and including the northern Plains
by early next week. The warm sector from the High Plains into the
Great Lakes/New England early in the week should see highs up to
10-15F or so above normal. Cold frontal progression should bring
temperatures closer to normal over most of the eastern half of the
country by mid-late week. Clouds and possibly lingering pockets of
rainfall should keep highs on the cool side over the Mid-Atlantic
during Sunday-Monday.
Tate/Rausch
Additional 3-7 Day Hazard information can be found on the WPC
medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw
Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Thu May 16 2024
Valid 00Z Fri May 17 2024 - 00Z Fri May 24 2024
...Heavy rain threat late week into the weekend...
Latest guidance continues to indicate that the deep upper low
initially north-northwest of the state and associated surface
boundary reaching the main islands will support a period of heavy
rainfall with flash flooding threats drifting from the central
islands into the western part of the state over the coming days.
Around Sunday there is lingering uncertainty in exactly when the
band of heaviest rainfall will ultimately reach west of the main
islands. From Monday onward expect light to moderate
east-southeasterly to southeasterly winds with a combination of
windward and sea breeze focus for showers.
As for details, there is fairly good consensus into the first part
of the weekend for the best moisture axis and focusing surface
boundary gradually shifting westward as the upper low drifts a
little farther away to the north. Sunday is currently more of a
question mark as some guidance says the axis of heaviest rainfall
could already reach just west of the western islands, but
consensus still depicts fairly high precipitable water (PWAT)
anomalies over the area. The 00Z ECMWF-initialized machine
learning models essentially split the difference, showing the axis
of highest QPF a little west but with some continued enhancement
into the state that would be consistent with the high moisture.
Trade showers from Monday onward should produce lighter rainfall,
though the combination of PWATs staying somewhat above normal and
upper level impulses could still provide some localized
enhancement.
Rausch
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Thu May 16 2024
Day 1
Valid 01Z Fri May 17 2024 - 12Z Fri May 17 2024
...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHWEST LOUISIANA AND A SMALL PORTION OF ADJOINING SOUTHEAST
TEXAS...
...01Z Update...
On-going flash flooding event will be shifting eastward...with the
focus gradually moving out of southeast Texas into Louisiana. The
area of highest rainfall rates have gradually been pushing
southward towards the Gulf of Mexico while simultaneously a complex
that was moved hrough the Houston area around 00Z and was
approaching the coastline as of 01Z has been the western edge of
the greatest flash flood threat with some upscale growth noted with
clusters north and northwest of Lake Charles. That suggests the
worst flash flooding threat will be shifting south of Interstate 10
and may even be offshore...especially in Texas...within the next 6
to 8 hours...and which should persist longer in Louisiana. Short
term high- resolution guidance has latched on the the system
becoming progressive and with a sharp cutoff to rainfall across all
of Texas by 05Z. Given the convection that continues to percolate
to the on-going complex in an atmosphere that has been thouroghly
worked over suggests the HRRR and ARW may be too quick to end the
QPF. Given the potential for overlap with the footprint of todays 2
to 4 inch rainfall...with embedded higher amounts...opted to keep
the high risk and moderate risk areas although both were shrunk
from earlier in the day. Kept the Slight Risk area extending
westward to cover the potential of active convection reaching areas
made hydrologically more sensitive earlier today. One offsetting
factor may be the increasing forward speed of this convection
although any additional rainfall could easily result in worsening
on-going flooding and lead to additional areas of flooding.
Kept a Marginal Risk extending north/northeastward along the
Mississippi River. Rainfall rates have not been particularly
dramatic during the day...but increasing flow of the particularly
moist airmass could still result in localized excessive rainfall
into the late evening hours.
Bann
...16Z Update...
The premise of the previous forecast remains the same with a
Dangerous and Life-Threatening flash flood event forecast across
portions of east TX through western LA. The recent trends in hi-res
guidance have allowed for a further consensus on where the heaviest
precip will occur, and the magnitude of the potential with the 12z
HREF probability fields very much outlining the upper end prospects
for not only flash flooding, but significantly impactful flooding
given the anticipated totals, rates, and antecedent soil moisture
for the area(s) of impact.
A couple of the probability fields that stand out include; 12z
HREF EAS probability for at least 3" is now upwards of 50-80%
within the confines of east TX from Trinity county to just across
the LA line. Probabilities above 60% for the EAS are statistically
significant due to how that probability is calculated and reserved
for higher end consensus amongst the hi-res deterministic and
time- lagged suite within the ensemble. Neighborhood probability
for at least 2"/hr rates have grown in areal coverage through the
period with a general 20-40% located from central TX down through
the Piney Woods area north of Houston. A bullseye of 50-60% is
located across east TX during the late-afternoon to early evening
hours across the above area as well, signaling the potential for
prolific rainfall within the expected High Risk zone. The last
statistically significant probability is the zone of >50%
probability for at least 5" based on the 12z HREF neighborhood
probability over east TX. 50-70% probabilities encompass the entire
zone within the forecasted High Risk, a positive correlation for
the potential and current forecast.
Precip totals within the latest HREF blended mean are now between
5-8" within the outlined High Risk as well, so the pattern is
favorable and becoming inherently agreed upon by the short term
guidance. This is a high-end flash flood potential for many across
TX through portions of the Lower Mississippi Valley as the complex
is expected to translate eastward into the Deep South by the end of
the period.
A SLGT risk was also added to portions of the Mid-Mississippi
Valley. More on that risk below...
...Mid-Mississippi Valley...
Increasing ascent within the right-entrance region of a
strengthening jet streak will provide sufficient forcing across
portions of northern AR up through southern MO and adjacent bounds
of KY/TN/IL. Surface cold front will lie to the north of the
aforementioned area with a defined warm sector positioned south of
the front. Weak shortwave pulse ejecting out from the southwest
will cross overhead after sunset with a percolating convective
field beginning over AR. As the impulse moves northeast, a steady
initiation of scattered thunderstorms will transpire over the above
region with rainfall rates capable of exceeding 1-2"/hr based on
the latest HREF probabilities for the respective hourly rates
(1"/hr exceedance probability of 50-70% across northern AR into
southeast MO). FFG indices are much lower over the AR/MO border
extending to the northeast due to multiple events that have allowed
for soil priming the past few weeks. With rainfall totals generally
between 1-3" with locally higher among the latest hi-res suite, and
HREF EAS probabilities for at least 1" now upwards of 60-70% with
2" around 20%, the prospects for localized flash flooding have
increased enough to warrant an upgrade to a SLGT risk across the
aforementioned portion of the Mid-Mississippi Valley.
Kleebauer
...Previous Discussion...
...DANGEROUS AND LIFE-THREATENING FLASH FLOODING LIKELY...
In coordination with HGX/Houston, TX; SHV/Shreveport, LA; and
LCH/Lake Charles, LA forecast offices, a High Risk upgrade was
introduced with this update. Dangerous and life threatening flash
flooding is likely in the High Risk area of the Piney Woods.
A vigorous shortwave trough leading a 110 kt zonal jet will move
across Texas today into tonight. Meanwhile, a moisture laden air
mass from the Gulf will advect north into eastern Texas today. The
air mass is characterized by PWATs that may exceed 2.25 inches,
which is above the 95th percentile for PWATs for this time of year,
and is over 3 sigma above normal. In portions of Louisiana this
exceeds the 99th percentile. All this to say, there will be plenty
of moisture for storms to work with as they move east. Instability
advecting northward with the moisture from the Gulf will approach
4,000 J/kg south of the line, but that level of instability will
further support very deep convection. The result is the expected
storms will be capable of extreme rainfall rates that may exceed 3
inches per hour with the strongest storms, but even with much of
the convection, 1-2 inch per hour rainfall rates will be common.
An impressive theta-e gradient over south-central Texas will push
northward on the low-level jet this morning. Some convection has
already fired across the Moderate and High Risk areas already this
morning, but it will take the arrival of the deep Gulf moisture
characterized by surface dewpoints will into the 70s to get the
storms going with daytime heating late this morning. An MCS is
likely to develop across north Texas late this morning with
embedded storms producing extreme rainfall rates. The line will
push southeastward rather quickly, but more convection developing
out ahead of the line, as well as training segments will make for a
rather small-width, but extended length line of convection that
could produce rainfall totals of 3-5 inches with local amounts as
high as 8 inches.
As the storms move into the High Risk area, a push of even deeper
moisture will greet the storms and allow them to further intensify
as they push east across the area. There has been better than
normal agreement in the overall guidance suite for multiple inches
of rain to occur as the storms move through, highlighting the Piney
Woods region for multiple days. With the full CAMs suite now
actualizing the event in the same place, confidence has increased
for the issuance of the High Risk.
AHPS data shows that the High Risk area has seen over 600% of their
normal rainfall for the past 2 weeks alone. Moderate to Major river
flooding is already ongoing in this area. Soils are not expected
to retain any of the rainfall expected today. Rates of 2 inches
per hour with locally higher rates will very quickly re-raise
levels in smaller creeks and streams, while the major rivers
already in flood stage will also see rises. Widespread flash
flooding with locally significant and life-threatening flash
flooding is likely as a result.
A couple cons still adding a bit of uncertainty to the forecast:
1) The cells will be fast-moving so any one area may only see the
extreme rainfall rates for a fraction of an hour, but training of
multiple storms capable of the high rates is expected over the High
Risk area. 2) Rain will only fall for 3-6 hours over the high risk
area as the strong storms move through. Thus, the 3-5 inches of
rain expected will fall over that much shorter time period. This
certainly raises the chances for flash flooding, but with no rain
expected following the storms, this does limit the severity of the
flooding expected somewhat.
As the storms push east across Louisiana tonight, they will weaken
a bit due to the loss of daytime heating and associated
instability, so amounts will drop off as the storms approach
Mississippi. This area has been hard hit with recent rains and
nearly saturated soils, but not as hard-hit as portions of Texas.
Thus, with decreasing rates, the risk areas trail off to the east.
However, there is considerable uncertainty as to how fast that will
happen and certainly where the storms will train towards the east
across Louisiana. Thus, the eastern boundaries of the Moderate and
Slight risk areas are more uncertain.
...North Central Texas...
Better agreement in the CAMs for an axis of heavy rain developing
along the aforementioned theta-e gradient this morning will allow
convection capable of very heavy rains to develop in the vicinity
of the Dallas-Fort Worth Metroplex. Most of the guidance suggests
the strongest convection will be on the west/Fort Worth side of the
Metroplex, so the threat is a little bit lower for Dallas. Nonetheless,
low FFGs characteristic of large cities will allow flash flooding
to develop much more quickly and with less rain than surrounding
areas. In coordination with FWD/Fort Worth, TX forecast office, a
Moderate Risk upgrade was introduced with this update. The
strongest storms will quickly shift south of the Metroplex this
afternoon, but lingering light to moderate rain may continue into
the evening, lengthening the duration of any flash flooding.
Wegman
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Thu May 16 2024
Day 2
Valid 12Z Fri May 17 2024 - 12Z Sat May 18 2024
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY INTO SOUTHERN AND CENTRAL ALABAMA...
...20Z Update...
Recent trends in guidance have shifted the heaviest axis of precip
for the D2 period a bit further south with the corridor extending
from I-55 in LA to the northeast through southern MS/AL into central
AL as the primary focus for heavy precip and flash flooding
potential Friday into Saturday. The area encompassed by the new MDT
orientation is the region most likely to be impacted by both the
remnant complex from the west that will move through the early
portion of the period, as well as the shortwave perturbation
ejecting out of the western Gulf into the Gulf Coast the second
half of the forecast. The latter is the period of interest with
regards to highest impacts with the current moisture flux anomalies
based within the latest NAEFS Climatological data set indicating
the low to mid-level moisture field reaching the 99th percentile
relative to climo across southeastern LA through parts of the Deep
South. With a strong mid-level vorticity maxima added to the
synoptic picture, this historically is favorable for widespread
convective initiation with a heavy QPF footprint given the
anomalous deep layer moisture field.
Probabilistically, the trends are slowly becoming more favorable
for the aforementioned area with the most daunting signal coming
from the 12z HREF neighborhood probability for at least 5" of
rainfall running between 35-45%, now centered over southern MS with
some probs of 20% dotted over parts of southeast LA through
southern AL. The 12z HREF EAS probabilities paint another picture
with very high probs for at least 1" of precip across much of the
Deep South, but a precipitous drop off once you move to 2" and 3"
with values more in-line around 10-20% which relays some of the
uncertainty in the eventual evolution of the pattern and the
expected heavy rain output. The environment will remain very
favorable for locally heavy rainfall with the region fairly
saturated from previous events, leading to lower than normal FFG
indices to exceed. This is one of the main reasons for the MDT
potential, and the rest becomes correlated to the expected multi-
round threat of convection during the beginning of Friday and
eventual impacts Friday night into early Saturday. After assessing
the mean QPF output and probability fields, as well as coordination
with the offices involved across the Southeast, we were able to
tighten the bounds of the Moderate Risk area and surrounding SLGT
as the pattern likely focuses in-of where the best instability
aligns with the flow running parallel to the frontal boundary
across the southeast. Mesoscale evolution pertaining to remnant
outflows from early convection will likely have a say on the,
"Where" the heaviest precip will occur as convection focuses along
those convergent zones. That will be contingent on short term
assessment, so there could be further shifts in the risk areas with
climo-based trends likely leaning towards a more southerly
adjustment in the higher-end potential. As of now, the MDT risk
extended from portions of southeast LA up through southern MS/AL to
south of Birmingham. SLGT risk extends back through Houston and
points northeast into west-central GA.
The second SLGT risk across portions of the Ohio Valley was
maintained given continuity in recent guidance for some scattered
heavy thunderstorms promoting local totals of 1-2" with locally
higher through the morning and afternoon hours Friday.
Kleebauer
...Previous Discussion...
By the start of the period 12Z Friday, the ongoing showers and
thunderstorms from the Day 1 period will be moving across the Day 2
Moderate risk area already. This first batch will quickly move off
to the north and east into central Alabama and Georgia through the
day, with occasional showers and storms following behind it.
The front that moved the LLJ advecting the impressive Gulf moisture
into the southern US will stall out across Louisiana, Mississippi,
and Alabama by Friday morning. With the LLJ no longer moving, the
low level southwesterly flow will align with the 90 kt upper level
jet streak. This will increase the potential for training storms,
if fast-moving, across the Moderate and surrounding Slight Risk
areas. Once the first batch of storms moves through in the morning,
there will be a relative break for much of the afternoon. However,
weak shortwave impulses tracking parallel to the jet streak may
still allow for occasional waves of storms to track across the
Moderate Risk area through the day.
Late Friday afternoon into the evening, the approach of a final and
strongest shortwave will reach the Slight and Moderate risk areas,
resulting in a "blossoming" of convection into the region. With
continued very high PWATs and instability, the storms will remain
capable of producing rates as high as 2 inches per hour, locally
higher with the strongest storms. Multiple rounds of storms are
likely through Friday night, which will result in storm total
rainfall through early Saturday morning of 2-4 inches with local
totals to 6 inches. The strongest and most prolific rain-makers are
expected during the predawn hours Saturday as the aforementioned
strongest upper level shortwave moves northeast across the Slight
and Moderate Risk areas.
Soils in this area are also quite saturated from recent heavy
rainfall, so it's expected that most of the rainfall through
Saturday morning will convert to runoff, resulting in scattered
instances of flash flooding with locally considerable flash
flooding.
In coordination with JAN/Jackson, MS; BMX/Birmingham, AL; and
MOB/Mobile, AL forecast offices, the Moderate Risk was expanded
northward into Birmingham and southward into Mobile, AL with this
update.
...Mississippi and Ohio Confluence Region...
Little has changed in the forecast for this region. A secondary
shortwave trough on the northern side of the jet stream will take
some of the Gulf moisture streaming in from the south and support
convection across the area. This convection will likely be ongoing
at the start of the period Friday morning, with any resultant flash
flooding starting soon thereafter. The storms will be capable of 1
inch per hour rainfall rates. Recent heavy rainfall along the Ohio
and Mississippi Rivers in this region have locally saturated the
soils, and additional rainfall amounts of 1 to locally 2 inches of
rain from morning convection may result in widely scattered
instances of flash flooding.
Wegman
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Thu May 16 2024
Day 3
Valid 12Z Sat May 18 2024 - 12Z Sun May 19 2024
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST...
...20Z Update...
Little change was necessary in the previous SLGT risk area due to
continuity amongst deterministic and subsequent ensemble output
with locally heavy rainfall possible across portions of the
Southeast extending from the FL Panhandle and coastal AL up through
much of AL/GA. Guidance remains privy to periods of scattered
convection over the Southeast due to a passing shortwave ejecting
out of the Gulf. Moisture flux from the disturbance is forecast to
hold within the upper bounds of climatological norms with the
recent NAEFS output signaling 850-700mb moisture anomalies between
95-99th percentile, a significant ingredient in the potential for
heavy rainfall within any convective schemes. Model output is
generally within that 1-2" zone with some higher QPF maxes embedded
in the QPF fields of deterministic. The potential is a bit capped
compared to the days prior given the expected instability forecast
and less organized in the convective evolution. There is a chance
the Gulf coast areas could be more favored early on in the period
pending the convective evolution upstream from the end of D2. The
contingency of prior periods is too much for any significant shift
in the risk potential, so decided to maintain what was inherited
from prior forecast package.
Further north, a secondary QPF max is plausible across portions of
the Mid-Atlantic with the best opportunity around southeastern VA.
Guidance is still all over the place when it comes to the threat
as, once again, the risk is contingent on previous convection and
the evolution into D3. The MRGL risk was maintained given the
uncertainty.
Kleebauer
...Previous Discussion...
The shortwave tracking across the Southeast causing the heaviest
rains of the Day 2/Friday period Friday night are now expected to
continue into the Saturday period, though from 12Z Saturday through
the morning, the convection should be on a weakening trend.
Nonetheless, given the expected rainfall the previous day,
continued abundance of moisture the thunderstorms can feed on, and
the influence of a strong positively tilted shortwave trough, a
Slight risk upgrade was introduced with this update, and the areas
have been shifted west due to slowing of the forward progression of
the upper level shortwave from previous runs.
By Saturday afternoon however, diurnal heating may allow for a
renewed round of strong thunderstorms as far west as Birmingham,
but more likely further south and east into southeast Alabama and
Georgia. These storms will be capable of 2 inch per hour rates, but
uncertainty with the convective evolution suggests a broad Slight
over the area is the best course of action until the convection
going on out west is better resolved. By Saturday evening, the
convection should be clear north and east of the Slight risk area.
Locally heavy rainfall is possible across southern Virginia
Saturday night. As with areas further south, given high uncertainty
by this point as to the convective evolution due to reliance on
that evolution for convective placement by this point, a Marginal
Risk was maintained for this area. Instability will also be limited
in as well. With better resolution and potential for higher
instability a Slight Risk may need to be considered in this area
with future updates.
Wegman
NWS Weather Prediction Center College Park MD
258 PM EDT Thu May 16 2024
During the Sunday-Monday night time frame covered by the Days 4-5
Excessive Rainfall Outlooks, the primary region of interest will
extend from the central Plains into the Midwest. A Plains surface
low should lift an initially stalling front northward as a warm
front while a wavy boundary should hang up for a time over the
Plains/Upper Midwest early next week while awaiting the approach of
western U.S. dynamics. There is still some scatter for details of
the placement for possibly multiple rounds of thunderstorms in this
area, but the ingredients of ample moisture/instability and lift
warrant continuing Marginal Risks in the EROs for both Days 4 and
5, with threats on Day 5 depending somewhat on how Day 4
transpires. From early Tuesday onward, expect northeastward
progression of developing low pressure to push the trailing cold
front and accompanying rain and thunderstorms of varying intensity
farther east and south. Rainfall amounts could be heavy across the
Midwest into the Great Lakes region, but other than that it will
take additional time to resolve most favored areas of heaviest
rainfall in the eastern and southern U.S. for the Tuesday-Thursday
time frame.
Aside from the north-central U.S., there is some concern Sunday
for locally heavy rain in the Southeast to southern Mid-Atlantic
with the departing low pressure system, but without enough of a
signal to warrant a risk area. Then in the West, initial upper
troughing will support some precipitation over northern areas with
scattered activity possibly reaching as far south as the Great
Basin. Some snow will be possible in the high elevations of the
Rockies, along with high winds possible on Sunday. Approach/arrival
of another upper low as currently advertised by midweek or so
would produce somewhat more organized precipitation at that time.
Changes in snow levels will depend on the depth of the upper low.
Expect South Texas to see multiple days of hazardous heat during
the period with highs persistently running 10-15F above normal with
max heat index values possibly reaching at least 110F. Highs near
or over 100 degrees could stretch farther north across the southern
High Plains at times. Some daily records for highs/warm lows will
be possible. Southern Florida may also experience hazardous heat
into Sunday with highs locally up to 5-10F above normal and max
heat index values reaching 105-110F, followed by continued above
normal but slightly less extreme readings.
The forecast pattern will favor below average highs over the
Northwest for most of next week, and including the northern Plains
by early next week. The warm sector from the High Plains into the
Great Lakes/New England early in the week should see highs up to
10-15F or so above normal. Cold frontal progression should bring
temperatures closer to normal over most of the eastern half of the
country by mid-late week. Clouds and possibly lingering pockets of
rainfall should keep highs on the cool side over the Mid-Atlantic
during Sunday-Monday.
Tate/Rausch
NWS Weather Prediction Center College Park MD
258 PM EDT Thu May 16 2024
During the Sunday-Monday night time frame covered by the Days 4-5
Excessive Rainfall Outlooks, the primary region of interest will
extend from the central Plains into the Midwest. A Plains surface
low should lift an initially stalling front northward as a warm
front while a wavy boundary should hang up for a time over the
Plains/Upper Midwest early next week while awaiting the approach of
western U.S. dynamics. There is still some scatter for details of
the placement for possibly multiple rounds of thunderstorms in this
area, but the ingredients of ample moisture/instability and lift
warrant continuing Marginal Risks in the EROs for both Days 4 and
5, with threats on Day 5 depending somewhat on how Day 4
transpires. From early Tuesday onward, expect northeastward
progression of developing low pressure to push the trailing cold
front and accompanying rain and thunderstorms of varying intensity
farther east and south. Rainfall amounts could be heavy across the
Midwest into the Great Lakes region, but other than that it will
take additional time to resolve most favored areas of heaviest
rainfall in the eastern and southern U.S. for the Tuesday-Thursday
time frame.
Aside from the north-central U.S., there is some concern Sunday
for locally heavy rain in the Southeast to southern Mid-Atlantic
with the departing low pressure system, but without enough of a
signal to warrant a risk area. Then in the West, initial upper
troughing will support some precipitation over northern areas with
scattered activity possibly reaching as far south as the Great
Basin. Some snow will be possible in the high elevations of the
Rockies, along with high winds possible on Sunday. Approach/arrival
of another upper low as currently advertised by midweek or so
would produce somewhat more organized precipitation at that time.
Changes in snow levels will depend on the depth of the upper low.
Expect South Texas to see multiple days of hazardous heat during
the period with highs persistently running 10-15F above normal with
max heat index values possibly reaching at least 110F. Highs near
or over 100 degrees could stretch farther north across the southern
High Plains at times. Some daily records for highs/warm lows will
be possible. Southern Florida may also experience hazardous heat
into Sunday with highs locally up to 5-10F above normal and max
heat index values reaching 105-110F, followed by continued above
normal but slightly less extreme readings.
The forecast pattern will favor below average highs over the
Northwest for most of next week, and including the northern Plains
by early next week. The warm sector from the High Plains into the
Great Lakes/New England early in the week should see highs up to
10-15F or so above normal. Cold frontal progression should bring
temperatures closer to normal over most of the eastern half of the
country by mid-late week. Clouds and possibly lingering pockets of
rainfall should keep highs on the cool side over the Mid-Atlantic
during Sunday-Monday.
Tate/Rausch
» Interactive Winter Weather Map (Day 4-7)
» Winter Storm Severity Index
+ Forecast Discussion (Day 1-3)
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
1031 AM EDT Mon May 13 2024
Valid 00Z Tue May 14 2024 - 00Z Fri May 17 2024
...WPC Winter Weather Desk no longer routinely staffed this
summer...
Pending any significant winter weather, the WPC Winter Weather Desk
will not be staffed this summer. The desk will resume continuous
staffing starting in late September 2024.
Most of the winter products from WPC will continue to be produced,
including the Winter Storm Severity Index (WSSI), Probabilistic
Winter Storm Severity Index (WSSI-P), and the Probabilistic Winter
Precipitation Forecasts (PWPF).
WPC
- » Experimental Winter Storm Outlook
- » Probabilistic Winter Storm Severity Index
- » Product Verification
- » Product Archive
- » Product Info
- » Forecast Surface Low Positions: Uncertainty Circles | Ensemble Clusters
- » Other Winter Weather Products
NWS Weather Prediction Center College Park MD
258 PM EDT Thu May 16 2024
Valid 12Z Sun May 19 2024 - 12Z Thu May 23 2024
...Overview...
Reasonably agreeable model guidance indicates that an upper trough
and surface low should move out of the eastern U.S. but linger in
the western Atlantic through the first half of next week.
Meanwhile, mean troughing will develop in the western U.S., which
along with frontal boundaries should help develop some locally
heavy convection across north-central parts of the Plains and
Mississippi Valley toward the Great Lakes region early to midweek.
Leading shortwave energy looks to push across the northern two-
thirds of the U.S. along with a cold front Tuesday-Thursday, while
an upper low drops south into the Northwest. Cool conditions with
increasing precipitation chances are forecast for the Northwest,
including higher elevation snow.
...Guidance/Predictability Assessment...
Recent model guidance is generally agreeable with the overall
pattern, with some typical detail uncertainties. There is still
some spread with the specifics of the eastern U.S. to western
Atlantic low, but the 00Z UKMET seemed to be the main outlier with
it in showing a farther east/progressive solution more reminiscent
of models from a couple days ago, so a GFS/ECMWF/CMC blend worked
well. Farther west, models indicate a few features of note that
combine into the western U.S. trough. A small southern stream
eastern Pacific closed low Sunday will track eastward and get
absorbed likely Monday-Tuesday, while northern stream energy pivots
through the northwestern and north-central U.S. within the trough.
00Z/06Z model guidance seemed agreeable with that but the new 12Z
CMC now lingers that energy in the West longer while other models
progress it into the Midwest. The new 12Z CMC also seems like an
outlier upstream as it does not show the upper low dropping south
through the western side of the trough by midweek.
The WPC forecast used a blend of the 00/06Z GFS and 00Z ECMWF and
CMC runs early in the period, with gradually increasing
incorporation of ensemble means to about half by the end of the
period. This maintained good continuity with the previous forecast.
...Weather/Hazards Highlights...
During the Sunday-Monday night time frame covered by the Days 4-5
Excessive Rainfall Outlooks, the primary region of interest will
extend from the central Plains into the Midwest. A Plains surface
low should lift an initially stalling front northward as a warm
front while a wavy boundary should hang up for a time over the
Plains/Upper Midwest early next week while awaiting the approach of
western U.S. dynamics. There is still some scatter for details of
the placement for possibly multiple rounds of thunderstorms in this
area, but the ingredients of ample moisture/instability and lift
warrant continuing Marginal Risks in the EROs for both Days 4 and
5, with threats on Day 5 depending somewhat on how Day 4
transpires. From early Tuesday onward, expect northeastward
progression of developing low pressure to push the trailing cold
front and accompanying rain and thunderstorms of varying intensity
farther east and south. Rainfall amounts could be heavy across the
Midwest into the Great Lakes region, but other than that it will
take additional time to resolve most favored areas of heaviest
rainfall in the eastern and southern U.S. for the Tuesday-Thursday
time frame.
Aside from the north-central U.S., there is some concern Sunday
for locally heavy rain in the Southeast to southern Mid-Atlantic
with the departing low pressure system, but without enough of a
signal to warrant a risk area. Then in the West, initial upper
troughing will support some precipitation over northern areas with
scattered activity possibly reaching as far south as the Great
Basin. Some snow will be possible in the high elevations of the
Rockies, along with high winds possible on Sunday. Approach/arrival
of another upper low as currently advertised by midweek or so
would produce somewhat more organized precipitation at that time.
Changes in snow levels will depend on the depth of the upper low.
Expect South Texas to see multiple days of hazardous heat during
the period with highs persistently running 10-15F above normal with
max heat index values possibly reaching at least 110F. Highs near
or over 100 degrees could stretch farther north across the southern
High Plains at times. Some daily records for highs/warm lows will
be possible. Southern Florida may also experience hazardous heat
into Sunday with highs locally up to 5-10F above normal and max
heat index values reaching 105-110F, followed by continued above
normal but slightly less extreme readings.
The forecast pattern will favor below average highs over the
Northwest for most of next week, and including the northern Plains
by early next week. The warm sector from the High Plains into the
Great Lakes/New England early in the week should see highs up to
10-15F or so above normal. Cold frontal progression should bring
temperatures closer to normal over most of the eastern half of the
country by mid-late week. Clouds and possibly lingering pockets of
rainfall should keep highs on the cool side over the Mid-Atlantic
during Sunday-Monday.
Tate/Rausch
Additional 3-7 Day Hazard information can be found on the WPC
medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw
Displays flood and flash flood reports as well as intense rainfall observations for user-selectable time ranges and customizable geographic regions. Includes ability to download reports and associated metadata in csv format.
Plots of GEFS probabilistic forecast of precipitation, temperature, and sea-level pressure exceeding various thresholds.
Custom plots of Local Storm Reports across the Contiguous United States. Reports include rain, snow, ice, and severe weather, as well as other significant information from storm spotters.
Displays the climatological significance of precipitation forecast by WPC. The climatological significance is represented by Average Recurrence Intervals (ARIs) of precipitation estimates from NOAA Atlas-14 and Atlas2.
An interactive situational awareness table that displays anomalies, percentiles, and return intervals from the GEFS, NAEFS, and ECMWF Ensembles (login required to view ECMWF data).
*Please note that there is currently an issue where only users on a NOAA network can access this page. We are actively working to resolve this problem.
Interactive display of where temperatures could approach or exceed records within the contiguous U.S. (based on NDFD temperature forecasts)
Displays Days 1-7 NDFD maximum and minimum temperatures, along with their respective departures from climatology.
An interactive tool that depicts areas of heavy snowfall from individual members of high-resolution short range ensemble forecasts.
Displays forecast information and its climatological context to quickly alert a forecaster when a record or neear-record breaking event is possible. This tool is available for both CONUS and Alaska.
Interface for specialized WPC Excessive Rainfall Outlook Maps for NWS County Warning Areas and States.
Change in weather parameters (temperature, dewpoint, surface pressure, etc) over the last 1/3/6/24 hours. Data is provided from the Real-Time Mesoscale Analysis (RTMA) or the Rapid Refresh (RAP).
The experimental National Weather Service (NWS) HeatRisk is a color-numeric-based index that provides a forecast of the potential level of risk for heat-related impacts to occur over a 24-hour period, with forecasts available out through 7 days.
Analog guidance that uses an objective approach to find historical events that are similar to the upcoming forecast.
Nationally consistent and skillful suite of calibrated forecast guidance based on a blend of both NWS and non-NWS numerical weather prediction model data and post-processed model guidance.
A portal for atmospheric river forecasts and diagnostics from the Center for Western Weather and Water Extremes.
An interactive display of time series plots from GEFS ensemble members at a point.
A variety of useful tools generated at The Storm Prediction Center (SPC).
Output from the ECMWF 'Ensemble Prediction System' (ENS) for four parameters: mean sea level pressure, 850 hPa temperature, 850 hPa wind speed, and 500 hPa geopotential height.