FOUS30 KWBC 160950
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
550 AM EDT Thu Jul 16 2026

Day 1  Valid 12Z Thu Jul 16 2026 - 12Z Fri Jul 17 2026

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTH-CENTRAL TEXAS...

...Texas...

0930Z Update...
A High Risk was introduced at 0930Z across portions
of south-central Texas. This includes areas where heavy rainfall
continues to fall and drift slowly to the north. Areas of slow-
moving, heavy rainfall are expected to continue beyond 12Z,
exacerbating the catastrophic impacts that unfolded across
portions of the region overnight. The Moderate Risk was also
expanded a little farther to the north to account for the current trends.

Previous discussion...
The persistent convective pattern centered near the Edwards Plateau
and southern Hill Country is expected to enter its final high-
impact phase this period. The high-end Moderate Risk has been
maintained over south-central Texas, centering on a corridor from
Val Verde and Crockett counties eastward into the southern Hill
Country. Extremely compromised soil conditions from multi-day
rainfall and very low flash flood guidance mean any additional
precipitation will exacerbate ongoing flooding. Convection that has
developed early this morning will likely linger past daybreak
around a slow-moving MCV, followed by another anticipated round of
locally heavy nocturnal storms late Thursday night into early
Friday morning. Both the HREF and REFS show robust probabilities
for additional rainfall totals exceeding 3 inches, with localized
narrow bands potentially reaching over 5 inches.

Farther north, the Slight Risk was extended into portions of
Northwest Texas. This expansion is supported by deep moisture
pooling along a low-to-mid level boundary, combined with shortwave
energy lifting northward out of the main system, which will fuel
scattered, high-rate convective cores capable of localized runoff concerns.

...Southwest into the Great Basin...

No significant changes were made to the risk areas out West for
this update. A prime monsoonal setup remains in place for southern
Arizona, where a Moderate Risk remains in place. PWs are expected
to climb above 2 inches, or exceeding 2 std dev normal, across
portions of southern Arizona. This moisture along with sufficient
instability and upper level support, will likely support terrain-
initiated thunderstorms. Subsequent rain-cooled outflows will drive
additional intense cells into the evening hours, pushing rainfall
rates up 2 inches/hr in some locations. A broader Slight Risk
encompasses much of Arizona, extending north into the slot canyons
of southern Utah and eastward into far western New Mexico.

...Mid Mississippi Valley into the Lower Ohio/Tennessee Valleys
and Southern Appalachians...

The Marginal Risk has been adjusted and expanded father east,
stretching from the Mid Mississippi Valley into portions of the
lower Ohio and Tennessee valleys, as well as the southern
Appalachians. A remnant mid-level shortwave moving into the region
will provide weak ascent. Southwesterly inflow into a downstream
boundary will support deepening moisture (PWs increasing to 1.75-2
inches). Both the HREF and REFS guidance are showing notable
probabilities for localized rainfall totals exceeding 2 inches.
Hourly rainfall rates along the boundary may support isolated flash
flood occurrences, particularly in complex terrain and urban areas.

Pereira
 

Day 2  Valid 12Z Fri Jul 17 2026 - 12Z Sat Jul 18 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF WEST
TEXAS, SOUTHERN NEW MEXICO, ARIZONA, AND THE SOUTHERN GREAT BASIN...

...West Texas into Southern New Mexico...

A transition and decay in the high-impact heavy rain setup across
the Edwards Plateau and southern Hill Country is expected as the
mid-level trough over West Texas weakens and begins to dissolve.
However, despite the trend, lingering elevated moisture beneath the
lower height field will allow for scattered activity, mostly
northwest of the areas most severely impacted earlier in the week.

While the general forecast totals are lower than previous days,
localized heavy rates may result in additional concerns, especially
in areas left vulnerable by prior rounds of heavy rainfall.

In southern New Mexico, storms are expected to develop along and
near the Sacramento Mountains by the afternoon and continue into
the evening before diminishing with the loss of diurnal heating.
Active wildfire burn scars in this region make it particularly
susceptible to rapid runoffs, supporting the continuation of the Slight Risk.

...Western U.S./Great Basin...

Overall, only minor changes were made to the risk areas in the
West, as a persistent monsoonal pattern remains locked in place.
A robust moisture profile will sustain widespread convective
coverage from southern Arizona north-northeastward into the Great
Basin. Moisture anomalies will remain high, with standardized
anomalies of 2-3 extending all the way from the Southwest to the
northern Rockies.

This moisture, along with with sufficient instability will support
highly efficient rainfall rates. A broad Slight Risk was maintained
from southern Arizona to southern Utah, with complex terrain,
urbanized areas, and other vulnerable areas likely to a be a focus
for the greater runoff concerns across the region.

...Ohio/Tennessee Valleys into the Central and Southern Appalachians....

A Marginal Risk covering much of the Ohio and Tennessee Valleys
into the central and southern Appalachians was maintained. Storms
developing across this region will be fueled by the same high-PW
airmass noted in the Day 1 period as it spread farther north and
east. These diurnally-driven storms are once again expected to
raise isolated runoff concerns.

...Northern Great Lakes...

A progressive upper trough digging southeast across central Canada,
will shift a notable jet max south into northern Minnesota. Strong
low level convergence along with favorable upper jet forcing will
support nocturnal storms from the Minnesota Arrowhead eastward into
Upper Michigan. Although fast storm motions will the heavy
accumulation and flash flooding threat, anomalous moisture
supporting heavy rates, along with some potential for brief
training, may raise isolated concerns.

Pereira
$$
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