FOUS30 KWBC 260031
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
831 PM EDT Mon May 25 2026
Day 1
Valid 01Z Tue May 26 2026 - 12Z Tue May 26 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
GULF COAST TOWARD THE SOUTHERN APPALACHIANS...
01Z Update...
Once again...the forecast reasoning has changed little so the
changes made to the Excessive Rainfall Outlook were largely driven
by trends seen in radar and satellite imagery. Locally heavy to=20
excessive rainfall is a concern in portions of Texas near a long-=20
lived convectively induced vort max over the central part of the=20
state. While coverage looks to remain limited...localized rainfall=20
rates on the order of 1 to 2 inches are possible with an associated
risk of flash flooding. From the Gulf coast northeastward to the=20
Southern Appalachians and a portion of North Carolina into the=20
south- central and southeast Virginia...showers and thunderstorms=20
will continue to impact south- central and southeast Virginia while
new convection develops across western North Carolina this evening
ahead of a slow-moving cold front. Intense rainfall rates of 1 to=20
locally 3 in/hr, combined with some cell-training, will yield=20
localized totals of 2 to 4 inches. Extreme rainfall rates may=20
overpower dry antecedent soils, especially in urban corridors.
Bann
16Z Update...
The meteorological rationale provided from night shift remains in
good shape. Within the large Slight Risk area in the Southeast,
the biggest concern is along the central Gulf Coast and farther
inland into south-central AL. Latest 12Z HREF showed moderate
chance probabilities (40-60%) for rainfall totals >5" from the NOLA
on north and east into southern MS. Southern AL and the western-
most portion of the FL Panhandle are also ideally placed within the
core of the anomalous >500 kg/m/s IVT that most CAMs show keeping
numerous thunderstorms producing 2-3"/hr rainfall rates in the
forecast. NASA SPoRT-LIS 0-10cm soil moisture percentiles are all
over 85%, indicating topsoil in the region will struggle to keep up
with these Excessive Rainfall rates. Scattered flash flooding is
of greatest concern along the central Gulf Coast this afternoon and
into this evening, with locally significant flash flooding
possible should pockets of >5" rainfall totals occur.
In west TX, 12Z HREF and REFS probabilities show that eastern NM
and central TX are most favored for localized flash flooding (as
eluded to in the previous discussion), but there are some CAMs
members sporting low chances (10-30%) for >2" of rainfall in West
TX between the two inherited Marginals. Given the messy convective
setup between the approaching trough to the west and the
stationary cut-off disturbance over central TX, opted to merge the
two Marginals together. In addition, 12Z HREF probabilities showed low-to-moderate chances (30-50%) for additional rainfall totals
along I-35 south of Dallas and low chances (10-20%) for >3" close
to the Austin metro area. The atmosphere may be worked over enough
to keep most thunderstorm activity isolated, but given the
urbanized corridor along I-35 potentially at risk, expanded the
Marginal into these areas for this afternoon and evening.
Mullinax
---Previous Discussion---
...Gulf Coast to Southern Appalachians...
Stagnant upper level pattern across much of the CONUS is allowing
for a continued confluent axis situated from the Central Gulf Coast
up through the Mid Atlantic states with ample moisture comprised of
PWAT anomalies running between +1 to +2.5 deviations above normal
within the aforementioned zone. Prevailing southerly flow in-of the
Central Gulf Coast will allow for the advection of yet another
mid-level pulse out of the Gulf by the beginning of the period with
sights on southeast LA through the Southeast U.S. Increasing instances
of heavy rainfall from convective development spurred by the
disturbance and deep moisture presence will invoke yet another
round of flash flood potential, mainly within those urbanized zones
littered across southeast LA up through southern MS, much of AL,
and eventually into GA by the afternoon time frame. Instability
parameters are well-within the mode to drive heavy rain prospects
with many of the forecast point soundings indicating appreciable
tall-skinny CAPE outputs historically prevalent for heavy rainfall
potential and enhanced rates.
00z HREF neighborhood probs for >3" are running between 40-80% in
the corridor expanding from New Orleans to the I-20 corridor in AL
with the bullseye focused over southwestern AL towards the MS
border. This zone has been consistently signaled as the primary
focus of heavier precipitation in-part to multiple convective
episodes in the period that could very well put down 3-5+" of
rainfall prior to the end of the D1. Despite higher FFG's locally,
rainfall rates between 2-3"/hr with higher intra-hour rates are
likely given the PWAT's between 1.8-2.1" over the course of the D1,
a good proxy for those higher end totals locally, especially in
any repeatedly impacted areas. This environment is respectable for
the time of year and regional instability parameters are more than
sufficient for even scattered heavy cell cores focused away from
the shortwave migration anticipated. All CAMs have some instances
of heavy rain across the Southeast U.S. extending to as far north
as the Tennessee Valley and as far east as southeast GA into
portions of the SC Low Country. A SLGT risk remains forecast for
the area of southeast LA up through the Southern Appalachians and
neighboring Piedmont in SC and all zones in-between. MRGL risk
expands away on either side encompassing a broad area outside the
SLGT.
...Mid Atlantic...
Remnant quasi-stationary front across the Central to Southern Mid
Atlantic will slowly lift north through the day Monday with
increasing moisture profiles being advected from southerly low to
mid-level flow around the northern periphery of a ridge in the
Western Atlantic. PWAT anomalies will shove closer to +2 to +3
deviations across a good portion of VA, especially areas south of
I-66 down to the VA Tidewater where PWATs are forecast to jump
above 2" as expressed via multiple global ensemble outputs. This
would set up a pretty deep warm cloud layer sufficient for higher
rainfall rates for any convective pulses that arise during the
forecast. The proximity of the front will be a focal point for
enhanced low-level convergence which can be seen very well within
the theta_E and omega cross-sections off both the 00z NAM Nest and
HRRR runs this evening. Pretty much all guidance has a narrow, yet
prolific corridor of heavy rain of convective origin aligned near
and just south of the front by later this afternoon and evening
with a steady stream of rainfall likely to cause some localized
areas of 2-4+" in the time frame of impact. Pending the model of
preference, some hit the corridor from Richmond to Hampton Roads
pretty hard while others are just a bit north, closer to the
northern neck of the Tidewater. In any case, either pathway would
be sufficient for flash flood prospects, even with the ongoing
drought in the area. Rainfall of 1-2"/hr will be likely in the
heavier cells with even some stronger cores capable of brief
2-3"/hr periods when you factor the anomalous deep moisture layer
in place.
If it was not for such elevated FFG's, this would likely be a
higher risk, but for now, maintained continuity with a MRGL, but
will have to monitor for exact placement of the repeating
convection as that could be enough to tip the scales to a focused
higher risk, especially if the immediate Tidewater is impacted as
that area has historically been flash flood prone due to more
sprawling urbanization and poor drainage capabilities.
...Texas into New Mexico...
Couple of areas of interest across the Southwestern U.S. into the
Southern Plains for Monday. The first is within the bounds of a
remnant MCV that continues to cause issues across Central and
Northern TX as it drifts over the northern Hill Country, west of
I-35 between San Angelo and Fort Worth. Spells of heavy rain
continue to plague this zone with cells popping up over the course
of the evening as focused low-level convergence and available
moisture aids in these scattered, slow-moving thunderstorms capable
of multiple inches of rainfall as they drift over the area. CAMs
are split on the handling of this feature heading through the
morning and afternoon today, but the models that do maintain
organization of the MCV tend to have another scattered to
widespread convective enhancement during the diurnal instability
max leading to pockets of enhanced rainfall between 2-4" in wake of
the cells. Modest neighborhood probs from the 00z HREF for >2"
(20-40%) exist in this relative corridor of the Concho Valley into north-central Hill Country between San Angelo and Fort Worth. With
the MCV likely to exhibit little forward propagation, areas that
were hit this evening could see more in the way of convection this
afternoon, so long as the MCV holds together and doesn't dissipate
as indicated via some guidance. Considering the variables at play
and the potential to be a sneakier setup overall, wanted to gauge a conservative approach and add a MRGL risk to the area referenced
above to cover for the threat.
Further west, we have a different setup that will induced by a
favorably developing upper trough/closed-low scenario coming out of
a negatively tilted shortwave trough ejecting out of the Desert
Southwest during the period. Height-falls are all but certain
within all model output with the shortwave progression likely
develop something more formidable as it encroaches on NM by later
this afternoon. Enhanced upper forcing and well-defined surface
trough bisecting far western TX up through eastern NM and the
divide will provide the necessary focused ascent features capable
for scattered to widespread convective development during peak
diurnal instability and beyond as the upper forcing pattern becomes
most favorable by the evening. Probabilities for rainfall rates
1"/hr remain highest within the confines of the surface trough as
indicated in the latest 00z HREF prob fields. The Sacramento
Mountains, adjacent High Plains of eastern NM down into the Upper
Trans Pecos are the most favored areas of heavy rainfall with
secondary maxima plausible in far west TX across the terrain in the
Guadalupe Mountains down to portions of the Davis and Delaware
Mountains in Southwest TX. The previous MRGL risk was expanded to
include more of the area comprised of at least modest probabilities
for >1" of precip, as well the more favored areas for rates >1"/hr,
at times during the period of interest.
Kleebauer
Day 2
Valid 12Z Tue May 26 2026 - 12Z Wed May 27 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL GULF COAST, AND CENTRAL TO WEST TEXAS...
20Z Update...
...Northern Rockies...
Main addition to this forecast cycle was to introduce a Marginal
Risk for portions of the Northern Rockies in collaboration with
OTX/MSO/TFX. As an anomalous 500mb low dives south from the Pacific
Northwest to the Southwest Tuesday into Wednesday, a strengthening
SErly regime will direct well above normal moisture at the
Northern Rockies beginning on Tuesday. By Tuesday afternoon, PWs
will exceed 1.0" in the Lewis Range and northern Bitterroots, which
are above the 99th climatological percentile for late May. Any
surface based heating will give rise to more instability for
developing convection to utilize, prompting the development of
thunderstorms that could generate 1"/hr rainfall rates. Add in the
proponent of upslope enhancement into the northern Rockies and the
stage is set for numerous thunderstorms over the rugged and complex
terrain of the Northern Rockies. Localized rainfall totals over 2"
are possible over northwest MT through Tuesday night. Flash
flooding is possible, most notably in areas near burn scars and
along complex terrain.
Otherwise, no other additions were made this cycle. The southern
Gulf Coast is of increasing concerning given the onslaught of
heavy rain these have received in recent days. Southern AL and the
FL Panhandle remain placed directly beneath a >500 kg/m/s IVT that
will continue to generate a fire hose of heavy showers and
thunderstorms. The 12Z HREF did show some low-to-moderate chance
probabilities (30-45%) for rainfall totals >5" for D2. Elsewhere,
the Marginal Risk in the OH Valley was expanded northward to
account for the rainfall footprint growing northward. Texas
continues to look very active, but guidance remains at odds on
which parts of the TX Hill County on north to the TX Panhandle will
see the heaviest rainfall. With no clearer picture given this
forecast cycle, maintained the inherited Slight Risk and only did
minor tweaks based on latest WPC QPF.
Mullinax
---Previous Discussion---
...Texas...
The previous D1 evolution will translate into a greater convective
regime as we head into D2 as the negatively-tilted trough axis
migrates further east into the Southern High Plains with a broad
diffluent axis pointed downstream of the mean trough. Increased
large scale ascent will become fixated over much of west TX,
spreading through the High Plains as widespread shower and
thunderstorm activity takes shape during the afternoon Tuesday. A
plethora of convective activity with relatively slow to modest
propagation speeds will translate into bouts of heavier rainfall
across the southern half of the TX Panhandle down through the
Permian Basin, western Rolling Plains, Concho Valley, and Stockton
Plateau leading to widespread 1+" totals with embedded 2-3" spots
given the convective regime. This setup is classic for scattered
flash flood instances, especially in those more urban zones and
areas of high low water crossing concentrations that are littered
over the Southern High Plains in west TX. The 00z HREF signal for
the 12z Tue to 00z Wed period is very aggressive for at least 2" in
spots over the Permian Basin and adjacent Caprock, including the Lubbock/Midland urban centers. Rainfall will likely be winding down
in these areas, but the setup will proceed to be more of a
nocturnal issue as we pivot our attention south over the Big Bend
and central RGV as a strong mid-level vorticity maxima ejects out
of Coahuila Tuesday evening and slides east into the Edwards
Plateau and neighboring Hill Country.
There's a general consensus on this setup across guidance with some
degree of broad heavy convection migrating into the above areas
enticing a dousing of rainfall as the pattern evolves overnight.
We'll see the introduction of a LLJ only add to the low-level
convergence regime spurred on by the expected evolution likely
allowing quite the rainfall signature in wake of the disturbance's
trajectory. US57 to I-10 is the prospectus area of interest, which
includes much of southern and central Hill Country with the very
end of the period likely to see some of the activity make it
towards the I-35 corridor near San Antonio. With the time frame
outside of the CAMs range, greater details aren't available for the
maximum potential in the forecast, but just given the current
environment conditions, there could be some localized areas >3" in
this second round of enhanced convection this period. The SLGT risk
from the previous forecast remains in effect, but will be
monitoring for any opportunity of a targeted higher risk, or at
least a higher-end threshold of the current SLGT.
...Gulf Coast and Southeast...
Confluent area on the western edge of a broad Western Atlantic
ridge and a trough centered over the Southern Plains will continue
for at least one more period with another round of convergence and
heavy convection focused over the Central Gulf Coast to areas
inland between southeast MS into the southern half of AL. This area
will have seen multiple days of impact from heavier convection to
begin with, so some priming of the soils could enact a greater
flash flood potential in general. This setup seems to be less
favored compared to the previous days, but still the guidance
remains favorable for 2-4" locally in the aforementioned areas
which would be enough to cause some scattered flash flood concerns
in those heavier cells that crop up. The general consensus seems to
target southern AL as the main focus with the area from Biloxi
over to Mobile and points north as the target of opportunity when
you assess the HREF blended mean QPF output and associated prob
fields for the 12z Tue to 00z Wed period. In any case, this is
still well within the standards of a SLGT risk which was maintained
from the previous forecast.
Kleebauer
Day 3
Valid 12Z Wed May 27 2026 - 12Z Thu May 28 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE EASTERN
HALF OF TEXAS, ARKLATEX, AND PORTIONS OF THE LOWER MISSISSIPPI
VALLEY...
20Z Update...
Just like for the D2 update, introduced a Marginal Risk for the
Northern Rockies in collaboration with OTX/MSO/TFX. PWs rise to
over 1.0" throughout much of the region, placing just about the
entire Marginal Risk area in a >99th climatological percentile PW
regime. The southeasterly IVT over eastern MT is also playing a key
role in the abundance of moisture across the Northern Rockies. Big
question will be the amount of instability available given
extensive cloud cover. But any added instability through daytime
heating combined with upsloping flow should trigger additional
thunderstorms capable of producing up to 1"/hr rainfall rates.
Aside from some minor tweaks to the threat areas from the Southern
Plains to the Mid-Atlantic based off latest WPC QPF, the rationale
for the forecast provided by the overnight shift remains in good
standing.
Mullinax
---Previous Discussion---
The broad upper level evolution occurring upstream over the
Southern Plains will continue to shift east with the large scale
forcing driving into the eastern half of TX leading to heavy rain
prospects over the eastern portions of Hill Country, the I-35
corridor and much of east TX, including the middle and upper TX
coastal areas. There's still some discrepancy in specifics on where
the heaviest precip will occur in this setup, but the mean QPF
output via various ensembles, including the National Blend and
ensemble bias corrected QPF targets the I-35 corridor over to the
Lower Mississippi Valley fairly heavily, considering the fact we
are still at D3. Widespread 1-3" totals are forecast within the
means with the environment favored for heavy precipitation
basically anywhere over the above areas referenced. A broad SLGT
risk is in place to encompass the area of potential, however some
fine tuning is likely to occur as we approach the period,
especially as we get more CAMs involved and we monitor how the
upstream pattern is evolving which will be the ultimate player in
the magnitude of rainfall and where.
Kleebauer
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!89ESUK0DP_0ag4t4ogHhGxPuis4e6chJK0IPWxj3rvh9= -TkbE84VoKPwrKUHjcuRTPHx9sPOfpfu3r1ht1A3Vlm7BnE$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!89ESUK0DP_0ag4t4ogHhGxPuis4e6chJK0IPWxj3rvh9= -TkbE84VoKPwrKUHjcuRTPHx9sPOfpfu3r1ht1A3FU2IRac$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!89ESUK0DP_0ag4t4ogHhGxPuis4e6chJK0IPWxj3rvh9= -TkbE84VoKPwrKUHjcuRTPHx9sPOfpfu3r1ht1A3VPsyZ_w$=20
=3D =3D =3D
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