Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
844 PM EDT Fri Jul 17 2026
Day 1
Valid 01Z Sat Jul 18 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...

0100Z Update...Only real change was the removal of the Marginal
Risk area in the Upper Peninsula of Michigan based on expected
forward speed of any convection that has yet to develop and the
lack of support from the HREF/RREF exceedance probabilities.
Otherwise, changes were more to adjust the boundaries of
previously-issued areas based on satellite or radar trends.

Bann

1600Z Update: There were 2 notable adjustments made to the Day 1
ERO, both within Slight Risk areas. The Slight Risk in western AZ
and far southeast NV was expanded westward a bit to include the Las
Vegas metro region, while the Slight across parts of Central TX was
expanded northward to include Abilene and areas east of Midland.
Both of these adjustments were based on current observational
trends (especially with the meso-enhanced vort lobe in TX), along
with the 12Z HREF and REFS QPF exceedance probabilities.

Hurley

Previous discussion...

...Western U.S....
A persistent monsoonal pattern will remain in place across the
West, supporting widespread convective coverage. Standardized
moisture anomalies of 2-3+ std dev extend from Arizona and
southern California to the northern Rockies, sustaining a broadly
unstable environment conducive to highly efficient rainfall.

A "high-end" Slight Risk remains centered along northern Arizona's
Mogollon Rim. The HREF and REFS guidance have remained consistent
in signaling the potential for localized amounts of 3+ inches in
this area, raising the potential for scattered to localized
significant flash flooding, especially given the already moist soil
conditions. Additionally, the Slight has been expanded eastward to
encompass portions of northeastern Arizona and northwestern New
Mexico, where HREF and REFS are also indicating the threat for
localized heavy amounts (2-3 inches).

Farther south and east, storms are expected to develop along the
Sacramento Mountains of southern New Mexico, threatening active
wildfire burn scars susceptible to rapid runoff.

...Texas...
Lingering mid-level energy over south-central Texas will slowly
track north and west on Friday. The overnight hi-res models
continued to suggest significantly less coverage of heavy amounts
than in previous days. However, remaining deep moisture, along
with a revitalized 30+ kt low level jet, will maintain at least a
localized threat for additional heavy rains and therefore a Slight
Risk covering much of Southwest to South-Central Texas was
maintained. Fortunately, the general consensus of the HREF and REFS
indicates the greater threat for heavy amounts will center west of
the areas most severely impacted earlier this week and closer to
the Davis Mountains today. Farther north, moisture and energy
lifting out will carry some potential for localized heavy rain and
perhaps isolated flash flooding into parts of Northwest Texas,
where a broad Marginal Risk was maintained.

...Western Florida...
A cut-off 500mb low lingering over the eastern Gulf will reside in
a favorable environment for highly-efficient rainfall (PWs at or
above 2 inches, MLCAPE over 1,000 J/kg, and deep warm-cloud
depths). This will easily support rainfall rates exceeding 3 in/hr.
Therefore, a Marginal Risk was maintained along portions of
Florida's West Coast, highlighting the potential for isolated
runoff concerns, especially in urbanized areas.

...Ohio/Tennessee Valley to the Central/Southern Appalachians...
A Marginal Risk was maintained as a broad, high-PW airmass
continues to spread north and east, with the expectation that
diurnally-driven storms may produce isolated, short-duration
runoff concerns this afternoon and evening.

...Northern Great Lakes...
A progressive upper trough and associated jet max diving into
northern Minnesota will initiate nocturnal convection from northern
Minnesota into Upper Michigan. While rapid storm motions should
limit widespread heavy accumulations, anomalous moisture and
localized training profiles may produce isolated runoff concerns
within the area highlighted by the Marginal Risk.

Pereira


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