FOUS30 KWBC 180826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Thu Jun 18 2026

Day 1
Valid 12Z Thu Jun 18 2026 - 12Z Fri Jun 19 2026

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL GULF COAST...

...WIDESPREAD AND POTENTIALLY LIFE THREATENING FLASH FLOODING
LIKELY TODAY FOR THE CENTRAL GULF COAST...

...Southeast...

The remnants of Post Tropical Cyclone Arthur are moving into the
Central Gulf Coast this morning. While the cyclone center may have
dissipated, the moisture plume and associated rainfall shield most
certainly have not. Rainfall moving into southeastern Louisiana
right now are producing rates to 3 inches per hour. These kinds of
rainfall rates are expected to continue with the strongest cells
for much of the day today across the central Gulf Coast. An
impressive 50 kt low level jet at 850 is advecting very deep
tropical moisture into the coast. This is pushing PWATs to over 2.6
inches. Meanwhile instability over the Gulf is up to 4,000 J/kg.
This is supporting very efficient cells capable of multiple inch
per hour rates to the east of the remnant circulation center.
Multiple waves of storms will track south to north across eastern
Louisiana into southern Mississippi this morning. The area has been
hard hit with heavy rain in recent days, so larger rivers are
already flooding, and soils are nearly saturated, so nearly all of
the heavy rainfall is expected to convert to runoff, resulting in
more significant river, stream, and creek rises though the morning.

The eastern side of the plume of moisture will spawn additional
numerous thunderstorms into southern Alabama and the Florida
Panhandle through midday. The storm organization is expected to
change a bit into the afternoon with peak heating. To the west
across Mississippi and Louisiana, backbuilding and training
convection is expected to form into 1 or 2 nearly stationary lines,
as the individual cells embedded within train towards the east
along the line. Meanwhile, over Alabama, multiple lines of eastward
moving lines of storms will get the flooding and heavy rainfall
started as early as mid-morning. The western end of the line in
LA/MS will become the trailing storms on the southwest end of the
MCS associated with post tropical cyclone Arthur. This line will
very slowly drift southeastward towards the Gulf Coast, likely
impacting Mobile and eventually the Pensacola area, as well as
points north. This will result in multiple hours from mid-afternoon
into the evening where training storms track over the same areas.
The eastward moving convection is expected to move faster towards
the east than the storms can backbuild, so the trailing line
responsible for the worst flooding should gradually shift east as
well. The storms could persist as long as until midnight in the
Florida Panhandle, but most guidance has it moving on and
dissipating earlier in the evening. Regardless, with potential for
multiple inch per hour rainfall rates with numerous storms through
the day tracking over the same areas, the storm total rainfall in
these areas is likely to pile up very quickly. Guidance suggests
rainfall totals in many areas of the High Risk could exceed 12
inches, though local amounts could approach 20 inches.

Widespread and potentially life threatening flash flooding is
likely as a result of these double-digit rainfall numbers. Urban
areas that could be impacted from New Orleans (in a higher-end
Moderate Risk), Mobile, and Pensacola could see life-threatening
flash flooding occur as a result. Everyone should heed the advice
of local authorities as warnings are issued.

Across central Alabama into northern Georgia, storm coverage and
intensity of the strongest cells are expected to be a bit lower,
but antecedent soil conditions remain nearly saturated. Multiple
hours of moderate to at times heavy rain are expected up as far
north as Birmingham and northeast as Atlanta. The Moderate Risk for
these areas remains in place with few changes. An eastward
expansion of the Moderate Risk in west-central Georgia was also made.

...Ohio/Tennessee Valleys...

A cold front pushing south across the Ohio Valley today will run
into the northern extent of the deep plume of tropical moisture
associated with the remnants of Arthur. With daytime heating, the
clashing of air masses along the front will result in numerous
showers and thunderstorms developing along the front, which will
likely be along the KY/TN border, extending ENE into eastern
Kentucky and southern West Virginia. The storms will be in a
favorable environment for training as the plume of moisture tracks
parallel to the front as well. A shortwave trough will help the
front advance south and east across the area more quickly this
evening through tonight, which should end any backbuilding and
training from the afternoon and allow everything to progress
eastward, ending the flooding threat.

...Southwestern Oklahoma into North Texas...

Overnight tonight, an MCS is expected to develop across
southwestern Oklahoma and north Texas in response to both proximity
to the dry line, deep tropical moisture with PWATs approaching 2
inches, and a developing low over West Texas, encouraging the
formation of a low level jet into the storms. Given this is a
smaller feature than the remnants of Arthur to the east, the CAMs
are struggling much more with where and how long the storms in the
area will form, and where they will track. Most likely the storms
will remain along the Red River/OK-TX border. The inherited Slight
covering most of the rest of Oklahoma into Arkansas was dropped to
a Marginal as this MCS should remain well separated from the rains
with Arthur to the east, with little rain in between.

Wegman


Day 2
Valid 12Z Fri Jun 19 2026 - 12Z Sat Jun 20 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR SOUTHERN
ALABAMA AND ADJACENT AREAS...

...Southeast...

While the plume of extreme moisture associated with the remnants of
Arthur will be exiting the Carolina coast at the start of the
period, deep tropical moisture will remain entrenched over much of
the Southeast on Friday. A cold front that tracked over the Ohio
Valley on Day 1/Thursday will continue edging southward into the
Southeast, bringing much drier air and relief to areas behind it.
Unfortunately ahead of it, the air mass will remain soupy. The
moisture off the Gulf will have turned eastward along the front on
Friday, which will do a couple things: 1) It will not prevent the
front from making more southward progress, as opposed to a
southerly low level jet which would actively work against a
southward moving front. 2) It will create a more unidirectional
wind flow through the depth of the atmosphere, which will support faster-moving, but training storms along the front. In addition to
any MCSs which could form in the soupy air mass early in the
morning, potentially multiple lines of storms will track
southeastward along the front into the area that just was hit with
Arthur's remnants the previous day. Thus, the Moderate Risk for
this area remains in effect. Expected rainfall for most areas will
generally stay between 1-3 inches on average, so the rainfall
amounts expected on Friday will pale in comparison to today.
However, given the expected flooding that will very much still be
ongoing on Friday, the addition of 1-3 inches of rain with locally
higher amounts where storm training persists longest over these
same areas still raised the flooding threat in the area to the
Moderate Risk category. Changes in where the heaviest rains
today/Day 1 occur may result in shifts of the Moderate Risk,
particularly if the heaviest expected rains occur further south and
west into Mississippi and eastern Louisiana. A few of the CAMs
models are hinting at that possibility.

...Southern Plains...

Across a large swath of Texas on Friday, multiple MCSs may impact
much of the state. On Friday morning, lingering MCSs from Oklahoma
and the Slight Risk on Day 1 may be ongoing into north-central
Texas Friday morning, including into the Metroplex. Widely
scattered instances of flash flooding will be possible with that.
More coverage of storms are expected Friday night. The typical
strengthening MCS will advect extreme instability and moisture over
all of the eastern half of the state. As storms form and organize
into MCSs, the potential for additional instances of flash flooding
will increase. There is considerable uncertainty as to where they
form and how they track, so a large swath of eastern Texas was
included in a Slight Risk, especially down towards San Antonio and
Houston, which have been impacted with heavy rains in recent days,
and soils remain wetter than normal.

Wegman
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* Origin: Capitol City Online (618:250/10)