FOUS30 KWBC 040827
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Sat Apr 4 2026

Day 1
Valid 12Z Sat Apr 04 2026 - 12Z Sun Apr 05 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE ARKLATEX/LOWER MISSISSIPPI VALLEY AND A PORTION OF THE 
SOUTHERN GREAT LAKES...

Much of convective evolution today depends on details about how 
much convection lingers and exactly where the convection is located
this morning across Arkansas and Texas. East-northeastward 
progression of a mid-level wave toward the Great Lakes will aid in
southeastward movement of a cold front into the ARKLATEX and Lower
Mississippi Valley Eventually, the front will oriented more 
parallel to weakening flow aloft supporting additional 
opportunities for training convection as storms organize along 
remnant outflows and backbuild, with the potential for areal 
average rainfall in the 1-2" range leading to isolated instances of
flash flooding. 

Maintained the Slight Risk area over portions of Texas and Arkansas
ahead of convection moving out of Oklahoma and northern Texas from
overnight prior of the start of the Day 1 period at 12Z Saturday.
Surface analysis showed a wave of low pressure along the front in 
northeast Texas will also help to maintain/enhance the development 
of this convection as well as briefly slow the progression of the 
front northeast through the ArkLaTex, allowing for heavier rainfall
totals as storms persist over the region for a longer amount of 
time before the front begins to sweep southward faster later into 
the afternoon. 

Also maintained the separate Slight Risk area to the east over portions
of the Lower Mississippi Valley later today as moist southerly flow
from the Gulf taps a pool of ~70 degree dewpoints and draws that
airmass northward. These high dewpoints along with daytime heating
will lead to a region of 1000-2000 J/KG CAPE supporting the 
development of heavy- rainfall producing thunderstorms ahead of the
front. The combination of this initial development in addition to 
a second round of storms expected along the front with similarly 
high rain rates of ~2" per hour will also lead to the potential of 
locally heavier totals in the 3-4" range. While dry antecedent 
conditions/high FFGs may limit the overall threat, the potential 
for these higher rain rates/totals within the highlighted Slight 
Risks should be sufficient enough for at least a localized/urban 
scattered flash flood threat.

Farther north, introduced a Slight risk area over portions of
northern Ohio and northern Indiana due to a combination of locally
heavy rainfall overnight falling on areas where the 1-hour flash
flood guidance was locally as low as 1 inch and the approach of a
front from the west which will potentially act to focus another
round of showers and thunderstorms. Rainfall rates are not likely 
to be all that impressive nor will the duration of the rainfall be
particularly long due to the progressive nature of the front and 
the strengthening flow aloft. Even so...recent rainfall has made 
the area more susceptible to problems with flooding and run-off.

Bann


Day 2
Valid 12Z Sun Apr 05 2026 - 12Z Mon Apr 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF SOUTH TEXAS ON SUNDAY...

Much like model runs over the past day or two...the suite of
numerical guidance from 04/00Z has continued to trend a bit faster
with the arrival of a cold front from the north. This adds to the
concern that moisture and instability will be swept out of the area
very early in the Day 2 period...if not before the period begins at
12Z on Sunday. Spaghetti plots of QPF continue to show enough
members with post-frontal amounts in the 1 inch to 2 inch range to
keep the Marginal in place...but the area continued to be
increasing confined to coastal areas and the deep south portion of Texas.

Bann


Day 3
Valid 12Z Mon Apr 06 2026 - 12Z Tue Apr 07 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann
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