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QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Wed Mar 4 2026

Day 1
Valid 16Z Wed Mar 04 2026 - 12Z Thu Mar 05 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE OZARKS AND THE OHIO VALLEY...

16Z Update...

Changes for this update include south and eastward expansions of 
the Slight Risk over the Ozarks to account for a generally heavier
convective footprint over eastern OK up across much of northwest AR
and southern MO. Multiple rounds of heavy showers and thunderstorms
across these areas over the next 12 to 18 hours will likely prime
the otherwise dry soils sufficiently to increase the threat for
runoff problems and some isolated to potentially scattered areas of
flash flooding. Increasing CAPE and rather anomalous PWs pooling up
along a strong frontal zone working in tandem with ejecting
shortwave energy should favor relatively organized convective 
clusters. The activity later today and tonight will be capable of
locally training over the same area given favorable deep layer
steering flow aligning with the frontal placement. Still thinking
locally 3 to 5 inch rainfall totals which is in good agreement with
the 12Z HREF probabilistic output.

An area to closely watch for this evening/overnight will also be
parts of central and northern TX (including the DFW metropolitan
area) as there are several 12Z CAM solutions (ARW/ARW2, HRRR and
RRFS) showing relatively slow-moving and rather discreet pockets of
convection with high rainfall rates in close proximity to the cold
front settling down across this region. Antecedent conditions are
dry, but the high rainfall rates, and slower cell-motions may
foster locally several inches of rain which certainly would drive a
threat for at least isolated flash flooding concerns and especially
if they manifest into a more urbanized environment. As such, the
Marginal Risk has been broadened down into these ares of central
and northern TX.

A Slight Risk has been introduced across portions of the OH Valley
including southern IN, southern OH, far northern WV and a small
part of northwest WV where locally a combination of additional
rounds of heavy rain (1 to 2+ inches) coupled with wet antecedent
conditions from recent rainfall will foster greater runoff
concerns. Already many areas this morning have lingering runoff
problems from last night's 1 to 3 inches of rain that fell, so the
additional rains will strongly contribute to elevated streamflows 
and runoff concerns.

Orrison

Previous discussion...

Upper air pattern from the Central Rockies to the Ohio Valley
remains relatively amplified with a deep shortwave trough analyzed
across CO, slowly ejecting out into the Front Range this evening.
At the surface, a weak surface reflection remains parked over
southwest MO with a trailing cold front analyzed back through OK
into the TX Panhandle. Expected evolution of the entire pattern
will yield a slow-moving cold frontal approach across the Southern
Plains with sights downstream on the Mid and Lower-Mississippi
Valley area as we move into the front half of D1. Defined confluent
flow within a persistent axis of diffluence across E TX into the
Mississippi Valley will allow for a continuation of convective
pulses to develop and propagate northeast along the trailing front
with a multi-wave complex of thunderstorms expected to impact areas
from north TX up through eastern OK, northwest AR, eventually
through southern MO. Relative instability remains modest, at best
ahead of the trough axis with general theta_E favored environment
located along and south of the cold front bisecting the above areas.

PWAT anomalies between 2-3 deviations above normal will enhance
heavy rain prospects within any cell maturation with a broad axis
of at least light to moderate rain likely ongoing from later this
morning, carrying through the afternoon. A brief period of
generally lighter rainfall is anticipated prior to sunset, however,
expectation is for round two to develop with the advent of the
budding 850mb LLJ positioned southeast of the surface low as it
finally begins to migrate east-northeast from southern MO. The
multi-wave precip forecast will allow for priming of the dry soils
currently in place across the Ozarks with forecasts of 3-5" totals
being projected via the latest CAMs in areas hit multiple times by
the waves. Widespread 1-2" are forecast surrounding with the
"bullseye" of precip aligned from far eastern OK up through
northwest AR into southern MO with the heaviest likely occurring
over the rugged terrain of the Ozarks between AR and MO. 00z HREF
neighborhood probs for >3" of rainfall are running between 40-80%
over the above zone with low-end probs (15-30%) for >5" across
southern MO, south of I-44. This seems to have a good consensus
when assessing the more conservative EAS probs with modest
probabilities (35-60%) for at least 2" running just east of
Springfield to just west of I-55.

Despite those drier antecedent conditions, longevity in the threat
for heavy rainfall given the dual-wave structure of the precip
field will allow for isolated to scattered flash flood prospects.
In coordination with the Springfield, MO and Little Rock, AR WFO's,
a SLGT risk ERO was introduced in the latest update encompassing
through areas from far eastern OK up through northwest AR into southern MO.

Kleebauer


Day 2
Valid 12Z Thu Mar 05 2026 - 12Z Fri Mar 06 2026

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

Kleebauer


Day 3
Valid 12Z Fri Mar 06 2026 - 12Z Sat Mar 07 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN PLAINS INTO THE MID-MISSISSIPPI VALLEY...

Pattern across the western half of the CONUS becomes highly
amplified as a potent upper trough migrate east off the Pacific
with sights downstream on the Rockies and eventually the Southern
and Central Plains as we move into the end of the week and beyond.
There's still some discrepancy on exactly where the heaviest precip
will arise as the meridional component of the upper levels will
certainly open the door for any areas across the Southern Plains
to Mississippi Valley to experience scattered to widespread heavy
rainfall prospects with the Southern Plains and Lower Mississippi
Valley likely the most susceptible to more prolific convective
modes. Given the positioning of central and east TX up through the
ArkLaTex within a persistent diffluent upper level regime and the
best instability maximum located within the fresh Gulf moisture
advection pattern thanks to prevailing south to southeast flow,
there is a growing concern for heavy rainfall to initiate and move
overhead in these general areas. This threat extends further
northeast into the Mid-Mississippi Valley as noted via precip
footprint off the latest ensemble blends, including the NBM and
bias-corrected ensemble. Deterministic is all over the place with
regards to specifics, however, and with the period outside CAMs
windows, it's a bit too early for a SLGT risk proposition with
still some time to discern details as we move closer. The MRGL risk
inherited was maintained, but expectation for an upgrade is
relatively high given the nature of the setup.

Kleebauer
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