FOUS30 KWBC 290824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Wed Jan 29 2025

Day 1
Valid 12Z Wed Jan 29 2025 - 12Z Thu Jan 30 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
NORTH TEXAS AND SOUTHEASTERN OKLAHOMA...

An upper level cutoff low ejecting out of the Southwest into the 
Plains will provide ample forcing for ascent (along with the left 
exit region of a ~120 kt jet streak) for a developing low over the 
Texas and Oklahoma Panhandles into tonight. Return flow of Gulf 
moisture, warmth, and instability ahead of the low will advect 
north across Texas and into Oklahoma and Arkansas today (and 
especially into tonight). The typical diurnal strengthening of the 
LLJ overnight will greatly increase the coverage and intensity of 
storms along the developing low's cold front across Texas 
(particularly after 06z), while the warm front locally increases 
lift into Oklahoma. The surface low will track north into Colorado,
contributing to a winter storm there. Meanwhile much of the 
convection will be associated with the cold/occluded front as it 
pushes east towards the Mississippi Valley. Since the upper level 
low will be slow-moving (though increasing in forward speed with 
time), this will allow the storms that do form to have a high 
likelihood of training over the same areas. Training convection 
will be of greatest concern as the storms are first forming over 
North TX and into southeast OK (where a targeted upgrade to Slight 
risk was made, given 00z HREF 40-km neighborhood probabilities for 
3" exceedance of 50-70%, and primarily over a relatively short 
period from 06z-12z Thurs). Soils in the area have been drier than 
normal, meaning most rainfall should (in theory) be beneficial, 
however the rapid development of rainfall rates of 1-2"/hr over the
dry soils may locally exacerbate the flash flood threat (due to 
hardened and compacted soil resulting in reduced infiltration and 
increased runoff). 

Churchill/Wegman


Day 2
Valid 12Z Thu Jan 30 2025 - 12Z Fri Jan 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE 
ARK-LA-TEX, OZARKS, AND MID-SOUTH REGIONS...

Thunderstorms will likely be ongoing on the northern and western
sides of the Slight and Marginal Risks at the start of the period
Thursday morning. A vigorous upper level cutoff low will begin to
rejoin the polar jet by Friday morning. Before it does so, 
however, it will provide the forcing for numerous showers and 
thunderstorms across much of the Mid-South and Ark-La-Tex region. 
A 50-60 kt LLJ will pump plentiful anomalously high Gulf moisture 
across the Ark-La-Tex region Thursday morning, as the trailing 
cold front provides ample forcing for showers and storms across 
Oklahoma and Texas (and depending on how much rainfall occurs in
the 6-12 hours prior to the start of Day 2, some ongoing flash
flooding for prior training storms may be locally significant in
portions of North TX into southeast OK, where probabilities for
excessive rainfall are towards the higher-end of the Slight risk
spectrum, being 25%+). The main limiting factor will likely be
decreasing instability (to around 500 J/kg of MU CAPE into Thursday
morning), which looks to be maximized across southern and central 
Texas. The greatest forcing looks to be displaced farther north 
(from the Ark-La-Tex north and east into the Mississippi Valley). 
This disconnect may help to diminish the flash flooding potential a
bit (though concerns are greatest where the best instability and
forcing may meet over aforementioned areas of North TX into southeast OK).

It appears that many of the storms will be associated with a line
that moves east across the area. However, storms embedded within
the line may move somewhat parallel to the line towards the
northeast, this will allow for the potential for training farther
upstream into portions of the Middle MS Valley and OH Valley. 
Since there will be plenty of Gulf moisture (PWATs above 1.5 
inches, above the max moving average using BNA as a proxy
sounding), the showers and storms will have the potential to cause
isolated to scattered flash flooding. By Thursday night the flash 
flood threat should diminish as the last storms cross the MS River 
with eastward forward speed of the storms increasing along with 
continued decreasing instability, thus diminishing the flooding 
potential with time.

Churchill/Wegman


Day 3
Valid 12Z Fri Jan 31 2025 - 12Z Sat Feb 01 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE PACIFIC NORTHWEST COASTAL RANGES AND FOOTHILLS...

A wetter pattern will take shape across the Pacific Northwest
region beginning Thursday night, as a series of storm system look 
to impact the area (originating from a closed low from the North
Pacific interacting with another closed low/digging trough moving
south along the west coast of British Columbia). After an initial
round of light to moderate precipitation late on Day 2 in the
coastal ranges and foothills, rainfall will become moderate to 
heavy at times throughout much of Day 3. While forecast maximum 
IVT values are relatively weak overall (500-700 kg/ms), a longer
duration event could lead to a more 'moderate' atmospheric river
event. 24 hour rainfall totals are forecast to generally range from
1-3" (though may locally exceed 3" in favored upslope terrain). 

Churchill

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