Quantitative Precipitation Forecast
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000
FOUS30 KWBC 140718
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
318 AM EDT Thu Mar 14 2024

Day 1
Valid 12Z Thu Mar 14 2024 - 12Z Fri Mar 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS AREAS FROM NORTHEAST
TEXAS INTO THE MID-SOUTH...

Starting around 12z Thursday, guidance depicts the potential for
training convection within an area of increasingly zonal and
unidirectional westerly flow to focus along a warm frontal zone
across northern Illinois/Indiana, which should maintain isolated
flash flood potential through the morning, although a weakening
trend in convection is expected by 18Z. Local amounts towards 3"
are possible here per the 00z HREF output.

From Thursday afternoon through early Friday, a shortwave moving
into the Corn Belt should provide sufficient difluence aloft along
with a southward- moving cold front is expected to provide a focus
for scattered to numerous thunderstorm development from the Ozarks
into western TN. While 500 hPa ridging is increasing, 700 hPa
temperatures are in slow decline across AR implying decreasing
mid-level capping. Temperatures at 700 hPa (6C+) based on the 03z
RAP imply that the heavy rain concerns should be mainly north and
west of LA, as does the persistent and strong 850 hPa southwest
inflow from the Gulf of Mexico, which should amp up the
precipitable water values into the 1.5-1.75" range. ML CAPE should
rise as high as 3000+ J/kg in the vicinity of the ArkLaTex. Storms
are expected to develop in a difluent area aloft east of a cold
low dropping into the Desert Southwest and foster local cell
mergers/training to support flash flood potential. The highest
potential for flash flooding should reside in and near Arkansas
where areas of 2 inch/hr rain totals with local amounts towards 5"
are expected to materialize. The Slight risk area continues to
depict potential for at least localized flash flood potential
through the overnight hours. The guidance has trended in the usual
direction -- southward -- so the risk areas have followed suit.
The southward guidance trend along with the low chances of 5"+ kept
the risk level as a high-end Slight for the time being, though a
Moderate Risk near the ArkLaTex can`t be ruled out at some point in
the future.

The Marginal risk area across central Texas continues with the
expectation that scattered thunderstorms would focus along a cold
front in that area late Thursday and train/repeat, boosting local
rain rates. The Marginal risk area across the Ohio Valley coincides
with the expectation that isolated to scattered, fast-moving
storms could train and promote isolated areas of 2"+/hour rain
totals with local amounts to 4" from afternoon through the
overnight hours.

Roth

Day 2
Valid 12Z Fri Mar 15 2024 - 12Z Sat Mar 16 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND NEAR
SOUTHEAST TEXAS AND PORTIONS OF THE SOUTH...

A cold front begins to accelerate to the southeast across the
Southeast as a broad upper level trough gains real estate across
portions of the Great Lakes and Upper Midwest, with the front
moving slower to the south into the Southern Plains as a cold low
in the Desert Southwest shows minimal movement and keeps the upper
level flow southwest to west- southwesterly which should slow the
surface boundary`s progression. This combination of systems
flattens the ridging across the Southeast and Gulf Coast.
Temperatures at 700 hPa suggest that the heaviest rainfall should
be north of southern TX, where temperatures are <6C, based on GFS
forecasts and ML CAPE should rise to ~3000 J/kg. An axis of
anomalous PW values, 1.5-1.75", will be seen near the front.

Another day of potentially widespread heavy rainfall is expected,
as hourly rain totals to 2.5" and local amounts to 4" remain
possible. There is the typical amount of spread with respect to the
position and maxima within the heavy rainfall axis, but the
overall model consensus suggests potentially heavy rains. Some
heavy rainfall is expected across areas of Mississippi, Alabama and
Georgia that have had above average precip over the past week or
two, resulting in higher stream flows and greater soil saturation
which continues to be the reason for the Slight Risk, over other
considerations. The Slight Risk area was split in two to depict the
bimodal distribution of the heavy rainfall pattern in the southern
tier of the country, with the eastern portions associated with the
progressive frontal zone/850 hPa confluence early on more
northerly and the western portions associated with the slow- moving
boundary shifting more southerly.

A separated Marginal Risk remains in and near portions of WV which
is typically more sensitive to heavy rainfall and where flash
flood guidance values remain relatively low near a progressive
section of the front. Hourly rain totals to 1" and local amounts
to 2" are possible there, which could exceed the flash flood
guidance values.


Roth

Day 3
Valid 12Z Sat Mar 16 2024 - 12Z Sun Mar 17 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
SOUTHERN TEXAS...

Difluence aloft ahead of an upper level low moving slowly across
Arizona teams up with a sagging front in southern TX to continue
the potential for heavy rainfall in the front`s vicinity. The
guidance has shifted southwest, which has led to a similar shift
in the excessive rainfall areas. Temperatures at 700 hPa imply that
the heavy rain threat should be mainly north of Deep South TX,
based on GFS forecasts. Inflow at 850 hPa from the Gulf should
pulse up to 25-30 kts at times, importing ML CAPE of 2000 J/kg or
so.  Effective bulk shear should be sufficient for organized
convection, capable of producing hourly rain totals to 2" and local
amounts to 4".

Roth


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt


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