FOUS30 KWBC 051246
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
746 AM EST Thu Mar 5 2026

Day 1
Valid 1245Z Thu Mar 05 2026 - 12Z Fri Mar 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE OHIO RIVER VALLEY AND THE SOUTHERN PLAINS...

13z Update: We sent a quick update to expand the Marginal risk 
into southeast OK. Ongoing convection is exhibiting some
training/backbuilding characteristics this morning. This activity 
is not being handled well by the high res guidance, but with 
recent cloud top cooling, upstream instability, and wind fields 
favorable for backbuilding...it seems probable that this convection
will persist for at least a few more hours resulting in a 
localized flash flood risk.

Chenard

...Ohio River Valley...

Potent mid-level shortwave propagation over the Central Plains will
continue over the course of this evening into D1 with a core axis
of diffluence centered over the Mid-Mississippi and Ohio Valleys in
the beginning of the period. Multiple vorticity maxima will eject
northeast out of the Ozarks area with a stationary front at the
surface bisecting areas from North TX up through the Ohio River
Basin. Moisture transport with the setup is pretty much aligned
parallel to the mean flow leading to more organized convective
clusters propagating along the front, disseminating some relatively
solid QPF output from Dallas up through the north-central Ohio
Valley. Models are in agreement on the shortwave propagation out of
the Ozarks this evening to migrate northeast with an eventual
secondary wave of heavy precip impacting areas along the Ohio River
Basin, including as far west at the confluence of the
Ohio/Mississippi Rivers and points east-northeast along the Ohio
River bordering KY/IL/IN/OH. Multi-day rainfall output will place
areas of IN/OH within another period of rainfall which is already
causing issues for places south of I-70 in both states.

Heaviest rainfall is progged to occur to the southwest with the
signal via the latest 00z HREF really emphasizing the corridor at
the confluence of the Mississippi/Ohio rivers up through the
KY/IL/IN border, much of which falling between the 12-21z time
frame today. Neighborhood probs for >2" are between 40-60% over the
aforementioned area with a few deterministic CAMs producing
between 3-5" over the time frame. Considering the nature of the
overlap of heavy rainfall occurring tonight and then again in the
morning/early afternoon, there was enough of a signal to add a MRGL
risk for the region in question.

...Southern Plains...

Stationary boundary across TX will lift north during the morning
and afternoon period today with a quick theta_E advection regime
taking shape across much of the Southern Plains. Upstream trough
axis pushing through the west will help to re-amplify the flow
across the South-Central U.S. with a low pressure center forming
across the Front Range with a trailing dryline maturing across the
western TX Panhandle up down through southwest TX. Increasing
ascent within the diffluent axis downstream of the longwave trough, ample
instability located downstream of the dryline, and increased bulk
shear profiles will promote a favorable instance of convective
development and maintenance of present updrafts. NAEFS PWAT
percentile forecast is pushing the 99th percentile via
climatological norms across the region from the Red River, north
through the western half of OK into southern KS by late this
afternoon and beyond. This is a testament to the anticipated
proliferation of convective cells within the favorable environment,
each of which will be capable of heavy rain cores with hourly rates
pushing 2-3"/hr at peak intensity as noted via some of the latest
CAMs. Despite this area signifying higher FFG's due to a dearth of
precipitation lately, this setup is conducive for stronger
convection as noted via the SPC's Slight Risk outlook for severe
weather focused within that area downstream of the dryline. A low-
end scenario for flash flooding is the forecast for this particular
domain just given the deep moist favorability, as well as the
organized convective pattern likely to exhibit some pretty hefty
rainfall in localized areas as the cells migrate to the east and
northeast. A MRGL risk was added for the region encompassing North
TX up through western OK into southern KS.

Kleebauer


Day 2
Valid 12Z Fri Mar 06 2026 - 12Z Sat Mar 07 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSISSIPPI VALLEY, INCLUDING THE ARKLATEX...

...ArkLaTex to Lower Mississippi Valley...

Highly amplified pattern across the western CONUS will shift
eastward over the course of the end of the week and weekend leaving
a broad axis of convective development downstream over the Southern
Plains up into the Midwest to the Mississippi Valley. Guidance is
beginning to come into agreement on the area located from northeast
TX up through the ArkLaTex to the western half of the Lower
Mississippi Valley a focal point for heavy, organized convection
capable of flash flood concerns. Instability and moisture presence
will not be limited in this synoptic evolution with a robust
meridional push of favorable theta_E's thanks to a funneling of
Gulf moisture poleward downstream of the mean trough. Slow-moving
cold front across the Central and Southern Plains will pick up
speed by the end of the forecast period with a defined warm sector
situated from the eastern half of TX up through the Missouri Valley
with PWAT anomalies pushing 2-3 standard deviations above normal
for the time frame. Ensemble bias corrected QPF is now pushing over
2" across the ArkLaTex with the convergence signal strongest over
the three-state region as the nocturnal LLJ is forecast to nose
into the area promoting the most favorable axis for organized
convection and eventual cell mergers after sunset. CAMs are still a
bit out of range for this threat, however the signals are already
creeping into the end of their temporal ranges with some already
showing 2" of precip with more to come across this area of the
CONUS. This setup is bordering textbook for these kinds of
convective evolutions and impacts which lends enough favor to
upgrade the previous MRGL risk inheritance to a SLGT risk for the
highlighted zones. This setup is one to monitor as short term
convective trends could adjust the risk positioning further west
thanks to the overall amplified evolution.

...Midwest...

Amplified pattern to the west will impact the north-central CONUS,
as well as the wavy stationary front over the Central Plains and
Mississippi Valley will lift rapidly to the north as a warm front,
allowing for a steady increase in regional buoyancy and deep
moisture presence. Upper pattern out west will evolve into a setup
that splits the main shortwave in two, ejecting a piece of the
mid-level vortmax rapidly to the northeast leading to lee
cyclogenesis over western KS, lifting to the northeast. The
combination of increasing shear and ascent at both the surface and
aloft will allow for a heavy convective conglomeration to
materialize over the Missouri River Valley and points east with
sights on the Midwest with a centroid over IA/Southern WI/Northwest
IL. The good news is the setup is progged to be moving quickly, so
any impacts will be short but locally intense. Localized flash
flood prospects are forecast for the above areas as the convective
pattern will promote rates between 1-2"/hr at peak intensity,
enough to approach, and/or eclipse the lower end of the FFG
thresholds in place. The previous MRGL risk was maintained as a
result with only minor adjustments made to the east and northeast
fringes to the risk area.

Kleebauer


Day 3
Valid 12Z Sat Mar 07 2026 - 12Z Sun Mar 08 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHERN PLAINS UP THROUGH THE LOWER MISSISSIPPI VALLEY...

As the longwave pattern across the western half of the CONUS
materializes and the surface reflections make their headway to the
east/northeast, the cold front trailing the primary low moving
into the Great Lakes will continue its progress through the
Southern Plains into the Mississippi Valley losing latitude as it
propagates to the southeast. As the low moves further away and the
setup begins to lose upper level favor, the cold front is expected
to "fan out" as it approaches the Gulf coast leading to convective
alignment along and just ahead of the front to slow its progression
with the mean flow becoming a bit more parallel to the frontal
alignment. Moisture and instability will be plentiful with the
environment primed from a rich Gulf moisture advection regime that
will take place the previous 48 hrs. Models are in agreement on an
axis of heavy QPF located from TX to points northeast over portions
of AR/LA/western TN/northwest MS. There will likely be an area of
3+" of precip as noted via modest NBM probs for the threshold
(10-30%) and 90th percentile QPF output pushing over 3" for part of
east TX into northern LA with widespread 2+" outputs surrounding.

This setup is notorious for conditions to prime and favor areas
further southeast just due to the better instability maxima and
deeper moisture layer ahead of the front naturally positioned
closer to the Gulf coast. Pending forward propagation speed of the
cold front, heavy rainfall could very well make a push towards the
I-10 corridor down by Houston to Lake Charles, but the jury is
still out for those areas. Higher confidence in heavy rainfall is
just north of there with the areas of the Piney Woods in east TX up
through I-20 into LA as the main targets at this juncture. High
FFG's will likely thwart considerable flood prospects, as well as
the setup promoting at least steady convective progress to lower
training concerns. That still doesn't mean those concerns would
alleviate at least scattered flash flood concerns, but there's
still more time to assess location specifics before interjecting an
upgrade at this time. For now, a broad MRGL risk was maintained,
but the threat will warrant some consideration of an upgrade as we
move closer in time and get into the CAMs temporal window(s).

Kleebauer
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