Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
750 PM EST Thu Mar 5 2026

Day 1
Valid 01Z Fri Mar 06 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...

Northwest TX/OK...
A mixture of organized and ordinary thunderstorms are expected
near and downwind of the intersection of the dryline and warm front
across portions of the TX Panhandle, Northwest TX, OK, and perhaps
southern KS. Precipitable water values, ML CAPE and effective bulk
shear are sufficient for organized thunderstorms, including
mesocyclones. The mid- level cap is in the process of breaking at
the present time, and the expectation is for the shower and
thunderstorm activity to become at least scattered in coverage
overnight. The combination of mesocyclones (capable of producing
heavy rainfall by themselves) and ordinary convection could result
in cell collisions which could locally amplify rain totals. The
deep layer flow becomes increasingly aligned out of the southwest,
bringing in the possibility of cell training, which also could
allow for heavy rains. Given the ingredients available, hourly
amounts to 2.5" and local totals to 4" are possible. However, three
hourly flash flood values are fairly high, implying that any flash
flood issues would be favored in urban areas and would be isolated
to widely scattered in nature. This is enough evidence to maintain
the Marginal Risk in place, which was modified to account for
recent radar reflectivity trends and the 12z REFS/18z HREF
guidance.


Ohio Valley...
Isolated to widely scattered showers and thunderstorms remain
across the region. The 18z HREF is a bit more emphatic with totals
than the 12z REFS, but the combined implication is that local
totals in the 1-2" range are possible overnight. Considering fairly
saturated grounds, left the Marginal Risk in a course of least
regret.


Roth


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...

20z Update: Only minor changes made to the inherited risk areas.
QPF has trended up a bit across eastern IA into northern IL and
southern WI, but activity looks quick moving. Thus flash flood
impacts are still expected to stay isolated.

Chenard

...Previous Discussion...

...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 SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY...

20z Update: We introduced a Slight risk across portions of TX into
MS, where a corridor of heavy rainfall is expected. The actual
extent and magnitude of the flash flood risk remains a bit
uncertain relating to how quickly activity propagates off to the
south and east. Some guidance supports a rather quick southward
propagation of convection, which could keep the flash flood risk
more isolated in nature. However, there should still be an
opportunity for some along axis training even with some southward
propagation. Upper level divergence is strong, PWs high and, while
weakening through the day, there is a corridor of low level
convergence. The CSU ML ERO also indicates a broad Slight risk,
with even some 25% probabilities depicted. Thus think there is
enough going for this event to justify introducing a broad Slight
risk with this update.

A Marginal risk was also extended as far north as western NY.
Plenty of moisture will advect northward along this corridor, with
as much as 500-1000 j/kg of CAPE as well. Thus while areal
averaged rainfall is not that impressive, there will be an
opportunity for locally heavy rates. With saturated conditions
over portions of the OH Valley, and some snow pack and frozen
ground over NY...these higher rates could be enough to locally
result in excess runoff and minor flood concerns.

Chenard

...Previous Discussion

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


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