FOUS30 KWBC 130830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Mon Jul 13 2026

Day 1  Valid 12Z Mon Jul 13 2026 - 12Z Tue Jul 14 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN PLAINS, SOUTHEAST U.S., AND SOUTHERN MID ATLANTIC...

...Texas into Louisiana...

Front analyzed over OK/AR will slip southward as we move into
Monday with an increasing axis of low-level convergence along and
ahead of the boundary. Environment across the Southern Plains into
the Lower Mississippi Valley can be best described as oppressive as
deep layer moisture from Gulf origin has made its presence known
over much of the South with much of TX into Louisiana as no
exception. Upper pattern across the CONUS will be liable to cause
some headaches over much of the southern tier of the U.S. as broad
upper ridging focused over the Northern Plains will lead to more
east to west migrations of disturbances rounding the base of the
ridge and entering these suitable convectively allowing environments.

The 00z HREF continued a trend of widespread convective coverage
anticipated in the D1 time frame with multiple areas of interest
spanning from the Carolinas over into the Southern Plains. The
primary targets for enhanced rainfall are currently positioned
within the Lower Mississippi Valley extending west through Central
TX, eventually with the western fringes located in the terrain of
southwest TX. Prob fields have become very bullish on the prospects
of locally heavy rainfall in several areas spanning west TX into LA
with the greatest neighborhood probs for >3" (50-80%) and >5"
(40-70%) located over east TX into the Sabine with an extension
along the I-10 corridor between Lake Charles to Lafayette. This
trend has been noted in successive HREF outputs with the ensemble
mean QPF now upwards of 2-3" over a large area east of I-35. Make
no mistake, however, the threat for excessive rainfall totals over
3" does not stop in these areas as multiple CAMs deterministic
signatures indicate a potential for significant rainfall in-of the
I-35 corridor extending west into Hill Country and the Edwards
Plateau the back half of the period. This setup would transpire
later in the evening with the additional support stemming from an
approaching mid-level shortwave migrating southwest under the guide
from the general 500mb pattern across the Central and Southern
CONUS. Weak LLJ will likely develop after 00z Tue across the RGV
and South TX with that evolution likely providing a bit more
enhancement in the boundary layer convergence scheme. Timing of any
energy and overall positioning of the front will be a major
dictator of what could transpire in the back half of the forecast,
so currently went with a high-end SLGT to cover the primary
concerns from southwest TX through central and southwestern LA with
a broad SLGT extending further east through the rest of the
Southeast and Southern Mid Atlantic (More of this area below).

This is a setup that could spell surprises considering a very
favorable environment in place that will likely assert some very
prolific rainfall rates at times as deterministic samples from CAMs
already indicating the possibility of >3"/hr rainfall prospects
across a good portion of TX into LA.

...Southern Mid Atlantic into the Southeast U.S...

Current UA and WV satellite analysis indicates a weak closed-low
located over central TN and a slow-moving quasi- stationary front
at the surface positioned over the Carolinas through the southern
Tennessee Valley into the Southern Plains. Sprawling upper ridge
centered over the Northern U.S. is really driving this anomalous
pattern with surface ridging extending from the Ohio Valley and
Northeast down towards the area of the front. The entire setup
provides a strong low to mid-level convergence pattern that is
driving quite an axis of heavy convection over the Carolinas this
evening with a ton of convection occurring earlier Sunday over much
of the Southeast.

Generally persistent 500mb setup will allow for a repeat of
widespread convection during the daytime hours, Monday, with
perhaps a small shift in the northern periphery of the coverage
further south compared to Sunday as high pressure filters in over
much of VA/WV and the Central Mid Atlantic. HREF blended mean QPF
remains bullish with widespread 1-2" totals located across western
and southern NC down through SC where the areal maxima is
positioned squarely along the eastern fringes of the Piedmont into
Low Country. A strong neighborhood and EAS signature exists within
the latest 00z HREF for >5" and >2", respectively, a textbook
indicator of at least scattered flash flood prospects over the area
in question. The most prominent signatures reside in SC with more
modest interpretations in the prob fields located over the
Southeast towards the northern half of GA/AL into MS. Despite
widely scattered coverage this past afternoon, several flash flood
warnings were necessitated thanks to a very efficient warm rain
process for much of the Southern U.S. as deep layer moisture and
very high regional theta_E's offered deep warm cloud layers noted
via widespread WBZ heights >14k ft when assessing both
observational RAOB's and forecast soundings from various CAMs.

In any case, this is a textbook, widespread SLGT risk prospect
considering the variables above and a general persistence in the
pattern. A SLGT risk now extends through much of the Southern
Appalachians, southern NC, and points south with the inclusion of
the western FL Panhandle and Central Gulf coast areas.

...Southwest U.S. into the Sierra's...

As the upper pattern remains persistent for areas further east, the
Southwest U.S. will lie within the western flank of the ridge
allowing for prevailing southerly flow aloft to advect deeper
moisture north and northwest allowing for greater convective
potential over a larger area as we move into Monday. Instability
fields are primarily weak for areas within the Great Basin and
interior CA, but are much more favorable for locations within the
Desert SW of AZ into the Mogollon Rim region. The combination of
increasing moisture (+2 standard deviation PWATs) and increasing
thermodynamic influences noted via improved MUCAPE fields will lead
to scattered heavy rain prospects across the more susceptible flash
flood areas located from the Sierra's down through the Desert
Southwest of CA/AZ for Monday. A MRGL risk is in place for the
period at these locations with the best threat likely over
southeastern AZ into the Mogollon Rim according to the latest HREF
prob fields for 1 and 3-hr FFG exceedance forecast.

Kleebauer
$$

--- Scorpio BBS
 * Origin: capitolcityonlinet.net * KY, USA (618:250/10)