FOUS30 KWBC 150903
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
503 AM EDT Mon Jun 15 2026

Day 1
Valid 12Z Mon Jun 15 2026 - 12Z Tue Jun 16 2026

...THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL FOR MUCH OF THE
TEXAS GULF COAST AND SOUTH TEXAS AS WELL AS FOR A PORTION OF WEST-
CENTRAL MISSISSIPPI...

...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, some
of the remnants of former east Pacific tropical storm Cristina.

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. This will make any storms that develop in
this environment having an almost unnatural ability to produce
heavy rain. 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


Day 2
Valid 12Z Tue Jun 16 2026 - 12Z Wed Jun 17 2026

...THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL FOR THE ENTIRE
TEXAS GULF COAST AS WELL AS FOR WEST-CENTRAL MISSISSIPPI...

...Texas Gulf Coast...

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.

...West Central Mississippi...

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


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 which includes some of the upper
level remnants of former East Pacific tropical storm Cristina will
interact 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 into western
Louisiana by Thursday morning. Immediately in advance of the center
of this low, heavy rains will continue into the upper Texas Gulf
coast and the Houston metro 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.

There remains considerable uncertainty as to how fast the low will
track up the Texas Gulf Coast towards the lower Mississippi Valley.
A faster progression may require a northeastward expansion of the
Slight to cover more of central Louisiana, and if even a bit faster
still, would re-impact western Mississippi late Wednesday night,
requiring a significant upgrade from the current blank ERO for that
area. Thus, significant changes are probable with future updates.

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.

...Midwest...

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


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...

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


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



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