FOUS30 KWBC 151924
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
324 PM EDT Mon Jun 15 2026
Day 1
Valid 16Z Mon Jun 15 2026 - 12Z Tue Jun 16 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
TEXAS GULF COAST AND SOUTHEAST TEXAS AS WELL AS FOR A PORTION OF CENTRAL-SOUTHWEST LOUISIANA AND INTO WEST-CENTRAL MISSISSIPPI...
16Z Update...
Changes to the previous day 1 outlook include some expansion of
the MDT risk over eastern TX and LA. This bridges the gap between
the two previous MDT risks and matches current radar and satellite
trends, along with the 12Z CAM suite of guidance. See MPDs 0417,
0418, and 0419 for more information. PWs were analyzed to be
extremely high and above 2.2-2.5" this morning along the western
Gulf Coast, CRP sounding analysis had 2.54" PWAT at 12z and would
be a max for the date. 12Z HREF and REFS neighborhood probs for
total rainfall amounts through 12Z Tuesday exceeding 8" are
concerningly high (10-50%) over a vast region between South Texas
and central LA to west- central MS along the I-20 corridor. This
remains consistent with previous forecasts. The best chances for
maximum local amounts to near or even exceed 10" appears in South
Texas and along coastal regions towards Matagorda Bay by Tuesday
morning as a slow- moving axis of heavy rain develops again late
overnight while meandering along the coast. This area east of a
developing mid- level low over South TX is expected to remain a
focus as increased southerly flow overruns the front/surface trough
draped inland from the Gulf Coast through Tuesday. Showers and
thunderstorms continue to produce rates above 2"/hr and could even
reach up to extremely intense rates of 4"/hr. These rates can
quickly overwhelm ground water infrastructure and lead to numerous
instances of flash flooding. Some significant impacts are possible.
Snell
Previous Discussion...
...Texas Gulf Coast and South Texas...
A very impressive setup for flash flooding will begin to unfold
along the Gulf Coast of Texas today, and will continue into future
days. The impressive ingredient is the sheer amount of moisture
that will be advecting north into south Texas and the Gulf coast
over the next few days in advance of a potent upper level low.
PWATs advecting into deep south Texas are likely to broach close to
record territory today, as they climb to as high as 2.75 inches.
This is a function of well above normal sea-surface temperatures in
the Gulf adding low-level moisture, and preexisting upper level
moisture from Cristina. The combination of these could fully
saturate the atmosphere up to the tropopause, with melting layers
as high as 17,000 ft. As the aforementioned upper level
disturbance approaches and lee cyclogenesis begins east of the
Mexico mountains tonight, expect multiple rounds of storms across
Deep South Texas to impact the area. A westward moving band may
start off around peak heating this afternoon, then as the
disturbance approaches tonight, a nearly stationary or slowly
eastward moving band is expected to develop overnight tonight which
will persist for much of the night as competing forcings create an
area of low level convergence over Deep South Texas. There is some
uncertainty as to where this convergence sets up, but it appears
it's most likely closer to the Rio Grande Valley on the western
side of Deep South Texas. Given the incredible moisture available
for the storms, localized cells could produce rainfall rates as
high as 5 inches per hour, with 3 inch/hour rates common. Despite
dry soils going in, these incredible rain rates will easily
overwhelm the areas experiencing them, resulting in widespread and
locally catastrophic flash flooding, especially in any towns or
cities that experience an extended duration of rainfall rates of
that magnitude.
Further north, the north-south oriented bands over Deep South Texas
will impact a strong but slow-moving cold front drifting
southeastward towards the Texas Gulf Coast. This will funnel the
prodigious moisture northeastward paralleling the coast. The storms
will follow, resulting in training. As in Deep South Texas, despite
slightly, and I mean only slightly lower PWATs, rainfall rates to 3
in/hr will be common with localized rates to 5 inches/hour here as
well. FFGs are significantly lower from Corpus Christi northeast to
Houston as compared with further south down the coast, thus, these
prodigious rainfall rates will have no trouble exceeding FFGs.
Frictional convergence of the onshore flow and the front will make
for nearly stationary bands of storms along much of the middle
Texas Coast. Thus, expect storm total rainfall amounts today easily
exceeding 3 inches, but localized amounts will be much higher,
perhaps approaching 8 inches, as noted by the HREF probabilities.
With some uncertainty as to how prolific the storm total rainfall
amounts will be, the Moderate Risk may need to continue to be
upgraded in the hardest hit areas through the day, especially if
those include urban areas from Brownsville through Houston.
...West-Central Mississippi...
The same incredible moisture plume as over Texas is already in
place across all of Louisiana and southern Mississippi this
morning. The same front as in Texas will be even stronger to the
east in Louisiana and Mississippi. Thus, with southwesterly LLJ
flow into this front, expect numerous thunderstorms to develop
across northern Louisiana and west-central Mississippi by midday
today. The storms will run into a "wall" that is the cold front,
forcing them to turn eastward, resulting in a well-defined line of
storms along the frontal interface. It appears this is most likely
to occur along the I-20 corridor. The heaviest rains will occur
from midday through sunset, after which there may be a break before
more scattered convection redevelops in the early morning hours of
Tuesday. Multiple inch per hour rates are likely with these storms
as well due to the deep moisture with PWATs at record territory
between 2.25 and 2.5 inches. Portions of western Mississippi have
been recently hard hit with heavy rains, resulting in wet soils,
and the Jackson area due to urban concerns is also vulnerable to
flash flooding due to heavy rainfall. In coordination with the
JAN/Jackson, MS forecast office, a Moderate Risk upgrade has been
introduced. While soils are less supportive of flooding further
west into northern Louisiana, persistent multiple inch/hour rates
along the I-20 corridor could result in an expansion of the
Moderate Risk with future updates.
Wegman
=20
Day 2
Valid 12Z Tue Jun 16 2026 - 12Z Wed Jun 17 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE ENTIRE
TEXAS GULF COAST INTO SOUTHWEST/CENTRAL LOUISIANA AND CENTRAL
MISSISSIPPI...
...Texas Gulf Coast...
20Z Update...
Today's update to the day 2 outlook included an expansion of the
MDT risk through central LA into central MS, which matches the
continuous plume of moisture and convergence axis extending
northeast from the strengthening mid-level cyclone over South Texas
early Tuesday. Expectations are for ongoing activity Tuesday
morning across coastal TX to gradually shift offshore during the
day, with lingering impacts crossing over from day 1. Some
uncertainty remains regarding a more consolidated area of low
pressure over the far northwest Gulf by Tuesday night and a
developing feeder band to the east-northeast of this low. Most
guidance keeps this highly efficient rain producing rain band
offshore, but if it makes it any distance inland extreme rainfall
and significant impacts for the TX Coast are possible.
Snell
Previous Discussion...
A plume of incredibly deep tropical moisture over the entire Texas
Gulf Coast will be in place at the start of the period Tuesday
morning. Ongoing lee cyclogenesis in advance of a strong upper
level disturbance will support continuous numerous showers and
thunderstorms in the onshore flow up the western coast of the Gulf
and into the Texas Gulf Coast. This disturbance will further
increase the amount of moisture available for the storms, as PWATs
rise to record territory in some areas, possibly exceeding 2.75
inches. Any and all storms that continue to develop ahead of the
low will be capable of multiple inch/hour rainfall rates, despite
the reduced instability in the early morning. When added to
Monday's rains, flash flooding is likely to continue all along the
Texas Gulf Coast until the low itself, which will track
northeastward roughly parallel to the coast passes a given
longitude, switching the wind direction from onshore southward to
offshore northwestward. Since the low will be barely moving, a
steady onshore flow across the middle and upper Texas Gulf Coasts
will continue to favor training storms impacting coastal areas,
with the Houston Metro remaining particularly vulnerable. Meanwhile
for the lower Texas coast, once the low moves offshore, the
northwesterly flow will dramatically decrease storm coverage and
intensity, though not completely shut it off due to the deep
moisture still in place even behind the low, with the front lagging
behind along the Rio Grande.
There is considerable uncertainty as to the northern and western
extent of the rainfall threat on Tuesday. The cold front bringing
much drier air will continue its progress south and east across
South Texas, so the threat will end from west to east during the
day. Meanwhile extensive cloud cover should limit instability well
away from the coast. Thus, the storms will have a progressively
narrowing portion of the Texas Gulf Coast that they will be able to
impact. Regardless, heavy rain will continue to impact the Lower
Texas Coast from the D1 period into Tuesday morning, and the heavy
rains will continue further up the coast throughout the period.
This supports a continuation of the Moderate Risk into the
southwest corner of Louisiana.
Wegman
...Lower Mississippi Valley to Southeast...
20Z Update...
Much of the Lower Mississippi Valley and Southeast will remain in
the favorable right-entrance region of a stout upper-level jet
centered over the southern Appalachians. This will allow for ample
moisture to flow northeastward out of the western Gulf and
thunderstorms to focus along a lingering stationary front.
Thunderstorms and widespread shower activity should start out well
inland during the daytime and then shift to focus along the coast
after sunset and overnight into Wednesday morning. The 12Z HREF and
REFS highlight coastal MS, AL, and the FL Panhandle as having
30-60% chances for 3" in 6 hours.
Snell
Previous Discussion...
Heavy rains across western Mississippi are likely to redevelop in
the same area along the I-20 corridor during peak heating Tuesday
afternoon, and perhaps in some areas never completely stop Tuesday
morning from any overnight rainfall. The front driving the heaviest
rainfall with the strongest storms will be completely stationary
over Mississippi, whereas in Louisiana and points west, it will
continue painfully slow south and eastward progress. Thus, when
storms refire Tuesday afternoon, they will be over many of the same
hard hit areas of central Mississippi as on Monday. Further east,
on Monday the storms will align east-southeastward from western
Mississippi to northern Florida. By Tuesday however, northward
progress of the front as a warm front will allow the heaviest
rains to impact further north into Alabama and Georgia. Despite a
lack of rain on Monday, the still wet soils across central Alabama
towards Birmingham and Montgomery may require an eastward
extension of the Moderate Risk area into central Alabama.
Regardless it appears western Mississippi will still be the area
that gets the most rain, especially over the combined 2 day period.
Rains in west central Mississippi should diminish with loss of
daytime heating Tuesday night with lingering storms pressing
southeastward toward southern Alabama and the Florida Panhandle
Tuesday night.
Wegman
...Southeast Florida...
Added a MRGL risk for the urban corridor of southeast FL for
Tuesday. PWs remain around 1.7-2.0" and the overall pattern remains
similar to previous days as an upper ridge axis remains near and to
the south of the region. This likely leads to a diurnal cycle of
thunderstorms developing along a weak axis of convergence along the
coast, with these storms slow to move and eventually weaken before
sunset. Given the overlap of these storms, the potential for 2"/hr
rates, and the highly sensitive urban corridor of southeast FL a
MRGL risk was introduced for this time period.
Snell
=20
Day 3
Valid 12Z Wed Jun 17 2026 - 12Z Thu Jun 18 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE UPPER
TEXAS GULF COAST INTO SOUTHWEST LOUISIANA...
...Upper Texas Gulf Coast into Southwest Louisiana...
A potent upper level disturbance with an incredibly deep moisture
plume over the western Gulf to continue a multiple day heavy
rainfall event over a small portion of the upper Texas Gulf Coast
on Wednesday. The disturbance itself will make better forward
progress during the period, moving from off South Padre Island at
the start of the period towards the central/western Louisiana
coastline by Thursday morning. Immediately in advance of the
center of this low, heavy rains will continue into the upper Texas
Gulf coast from the D2/Tuesday period. The axis of heaviest
rainfall through the day is likely to be directed east of Houston,
along the Texas/Louisiana border near Beaumont. Thus, this area is
likely to see the worst impacts from flash flooding overall through
the day. The strongest storms will become increasingly tied to the
movement of the surface low and attendant upper level shortwave,
as the front that plagued much of Texas will follow behind the low,
clearing much of the rest of the state from heavy rains for a
brief time. Across the South, the front that was stalled from
central Mississippi through Georgia the past few days will
dissipate entirely in advance of the next strong cold front.
tracking across the Midwest.
Uncertainty remains with the speed and therefore eventual eastward
progression of this are of low pressure, which impacts where
confidence exists in flash flood impacts by Wednesday. Guidance
today has trended faster and east, which prompted the expansion of
the MDT and SLGT risk areas across LA. More changes are likely as
guidance comes into better agreement on the location and speed of
this system.
Since the upper Texas Coast area will have been hard hit on 2
consecutive days prior to Wednesday, the Moderate Risk continuation
into Wednesday was needed due to likely ongoing heavy rains through
the period. While there's better certainty into southwest Louisiana
for Moderate Risk level heavy rains, the Houston Metro was included
in coordination with HGX/Houston, TX forecast office due to
uncertainty largely on Wednesday morning as to how far west the
heavy rain shield will extend at that time. If guidance continues
to hedge eastward the risk level could be lowered for southeast TX
on Day 3.
Wegman/Snell
...Midwest...
20Z Update...
Only change to this outlook area with to shrink the MRGL and SLGT
on the northern section of the area where instability will be
limited across central WI and the northern L.P. of MI.
Otherwise, the forecast for scattered flash flooding appears to
remain consistent with latest model guidance.
Snell
Previous Discussion...
A potent area of low pressure over the Plains at the start of the
period will progress east across the Midwest at a rather fast clip
through the day on Wednesday. As the low moves into the mid-
Mississippi Valley, it will increasingly tap into the large
moisture plume present across much of the Southeast. The low will
create its own moisture feed allowing the moisture to rapidly
advect into the Midwest ahead of the low. The area from northern
Illinois into Indiana has also been hard hit by periodic rounds of
heavy rain in recent days, allowing for moist soils and high river
levels to remain. Light rains at times are expected in the area
Tuesday afternoon and evening, but due to lack of moisture, no
significant flash flooding concerns are expected then. By Day
3/Wednesday however, the tap into the Gulf moisture will change all
that. Numerous showers and thunderstorms will develop along the
cold front ahead of the low as PWATs rise well above 1.5 inches,
reaching as high as 2 inches at times. This will support storms
capable of 1-3 inch per hour rainfall rates Wednesday afternoon
through the overnight. The storms will be very fast moving, which
will reduce the flooding threat, but the aforementioned moist
soils, urban concerns, and increasing availability of deep moisture
will all support the potential for widely scattered instances of
flash flooding.
Expect a warm front to move across the area around midday to early
afternoon, then a strong cold front to move through late afternoon
through the evening, which may consist of one or 2 lines of storms.
These lines of storms in rapid succession could support training-
like effects as far as flash flooding potential. Given the very
favorable hydrology for flash flooding, it's possible targeted
Moderate Risk upgrades may be needed for portions of the area,
particularly northern Illinois into northern Indiana, where a
higher-end Slight is in effect.
Wegman
=20
Day 4 and Day 5
Valid 12Z Thu Jun 18 2026 - 12Z Sat Jun 20 2026
...THERE IS A MODERATE SLIGHT RISK OF EXCESSIVE RAINFALL FOR
PORTIONS OF THE LOWER MISSISSIPPI VALLEY & CENTRAL GULF COAST ON
DAY 4...
20Z Update: The main changes for the D4 period were the expansion
of the risk areas, including the MDT risk, further eastward to
account for the trends in being slightly faster with the PWAT surge
and mid-level vorticity ejection. This was noted within the global
ensemble means and correlated with a slight uptick in the pQPF
probs for the 1/2/3 inch thresholds. Maxima within the probs was
noted across south-central MS, expanding east to right around
western AL. Highest confidence given probability consensus was
across southern MS, so decided to align the MDT over the region
encompassing much of the Jackson, MS CWA bounds. The SLGT risk was
also expanded further east and north to account for the anomalous
PWAT advection regime anticipated by mid-week and beyond. The
expansion was to target the southern Appalachian front with
emphasis on northern GA into the escarpment of SC and western NC.
We'll be monitoring the trends closely as a further east push would
indicate a further expansion of the risks to the east, including
more of the I-20 corridor where Birmingham, AL and even
potentially Atlanta, GA becoming in play for a higher risk. In any
case, it's certainly the period to watch in the medium range for
enhanced impacts.
D5 is when we hit the back end of the more appreciable rainfall
prospects, however lingering deep layer moisture of tropical origin
will still allow for efficient warm rain processes and the ability
for continued heavy rainfall through a good portion of the
Southeastern U.S. up into the Southern Appalachians. The main
change was an expansion of the SLGT risk further north through the
southern Appalachians with a northern advancement into southwestern
VA. There's some discrepancy on the eastward extent of the
heaviest precipitation, however there was enough consensus to bring
the SLGT north in the terrain and maintain the high-end SLGT
posture across the Central Gulf coast into interior AL/MS.
Kleebauer
..Previous Discussion..
Attention is on the multi-day Excessive Rainfall threat in the
Deep South where an abundance of tropical moisture will engulf
areas from southeast TX to as far east as GA. There are notable
timing differences across guidance on the placement of the heaviest
rainfall, and this will come down in large part to the development
of the low-level disturbance in the western Gulf. Both its
development and track will likely be troublesome for guidance to
key in on for another 24-36 hours until the circulation is formed
over South TX. That said, the region in total will have witnessed
multiple rounds of Excessive Rainfall, particularly east TX,
central and northern LA, and into western MS in lead up to Day 4.
The 12Z ECMWF EFI showed a notable overlap of >0.7 signals from
southwest LA on east into central MS, including at least a 2
contour on the Shift of Tails. In collaboration with several WFOs
along the central Gulf Coast and the Lower MS Valley, a Moderate
Risk was issued to account for the concerns of additional Excessive
Rainfall over areas that will likely be dealing with ongoing flash
flooding in the days leading up to Thursday. It is worth noting
that the same axis of anomalous moisture in the South will stream
north into the TN/OH Valleys. These areas will have the benefit of
strong synoptic-scale forcing to produce widespread thunderstorms.
A Slight Risk stretches as far north as southwest PA to account for
flash flooding in these more flash flood prone areas.
Day 5 will see a weak 500mb trough axis over central TX tap into
lingering tropical moisture along the Gulf Coast. Lower pressures
over the Rio grande and persistent high pressure east of the
Bahamas will maintain the seemingly endless moisture tap emanating
out of the Bay of Campeche. Moisture out ahead of the upper trough
will also collide with a frontal boundary that will extend across
much of the South. The future of the upper-level feature that
originated over South TX early in the week may also still play a
key role in Excessive Rainfall, especially from southern LA on
east into northern GA. Accounting for various ensemble guidance
tonight, there is a sufficient signal for Excessive Rainfall in
areas across the South that received copious amounts of rainfall
the first four days of the work-week to be concerned for more
scattered instance of flash flooding that could be locally
significant. A Slight Risk was issued from the Lower Rio Grande
Valley to as far east as the Appalachians of northern GA.
Mullinax
=20
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8NBsLH2FQt75xA46yzxeKQR93HjEGDedLToSzIoM6aCG= kQFdIEWarBJRy-SLzXl1PqUGguKPQpMyyCzZ9qkoY6uQZXI$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8NBsLH2FQt75xA46yzxeKQR93HjEGDedLToSzIoM6aCG= kQFdIEWarBJRy-SLzXl1PqUGguKPQpMyyCzZ9qkoYjZJ9sU$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8NBsLH2FQt75xA46yzxeKQR93HjEGDedLToSzIoM6aCG= kQFdIEWarBJRy-SLzXl1PqUGguKPQpMyyCzZ9qkoGpq3rBs$=20
$$
=3D =3D =3D
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