Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 PM EDT Thu Jun 18 2026
Day 1
Valid 16Z Thu Jun 18 2026 - 12Z Fri Jun 19 2026

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

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

...1600 UTC Update...

A widespread and life-threatening flash flood event is underway
across the central Gulf Coast and will continue to expand
northeastward deeper into the Southeast throughout the day. Flash
flood emergencies have already been issued both in southeastern and
central LA as well as southern Mississippi where bands of
backbuilding, training thunderstorms have already lead to MRMS
estimated rainfall totals of 9-11" (see WPC MPD #450 for more
details). Torrential rainfall is expected to continue throughout
the day with these ongoing storms as well as additional bands of
thunderstorms supported by a surface low associated with the
remnants of Tropical Storm Arthur, an impressive ~40-50 kt low
level jet off the Gulf, and daily-record level PWATS over 2". Some
modest adjustments were made to the inherited outlook based on
ongoing thunderstorms and the latest 12Z hi-res guidance including
a westward expansion of the High Risk to central Louisiana where
ongoing life-threatening flash flooding is occurring. A slight
northeastward expansion was also included across southern
Mississippi and Alabama given moderate to high probabilities from
the HREF of 5-8"+ of rainfall. Guidance in general has suggested a
northeastward expansion of the flash flood risk bringing heightened
concern to southwestern to central Georgia as well as further
north into the southern Appalachians.

Elsewhere, the Slight Risk over portions of the southern
Plains/Texas was also expanded based on the latest 12Z hi-res
guidance. Thunderstorms are expected to develop later this evening
and into the overnight hours in vicinity of a wave of low pressure
along an approaching cold front and southward along the dryline.
Sporadic/slow storm motions and clustering of storms will support
locally heavy rainfall, especially if the collective
clustering/merging of cold pools can result in more organized
complexes as suggested by some of the hi-res guidance. This
includes both along the Red River Valley, where a Slight Risk is
already in place, as well as further south along the dryline into
the Texas Hill Country where the Slight Risk has been expanded.
Some of the latest hi-res guidance (including the RRFS) is more
bullish on the potential for heavier rainfall spreading southward
given expected storm motions and potential for a more organized
complex to develop.

Another round of thunderstorms is expected today over portions of
Arizona and New Mexico where some locally heavy rainfall/isolated
flash flooding will be possible given heightened moisture in place.
Most storms will likely be diurnally driven along the more complex
terrain. Increased moist southerly flow off the Atlantic into
interior New England/Upstate New York ahead of an approaching low
pressure system will also bring the threat for some locally heavy
rainfall (1-3" totals) and isolated flash flooding.

Putnam

...Previous Discussion...

...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 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt