Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
854 PM EDT Thu Oct 29 2026
Day 2
Valid 12Z Fri Oct 30 2026 - 12Z Sat Oct 31 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST...

...Southwest...
Broad troughing will develop over the West with embedded shortwaves
moving across portions of the area on Friday. Meanwhile, a strong
southern stream jet will approach Baja California, placing Arizona
under the favorable left exit region with enhanced upper level
divergence Friday afternoon. Southerly low-level flow will direct
Pacific moisture into the area as well, bringing PWATs up to 1-1.4
inches across the southern half of Arizona (2-3 standard deviations
above normal), more typical of values during their summer monsoon.
This warm, moist air mass will also increase instability, with
MUCAPE values forecast to reach 1000 J/kg across much of southern
Arizona. With favorable conditions throughout the atmospheric
column, scattered to widespread convection is expected to develop
with the passing of the upper shortwave Friday afternoon and
evening.

The available ingredients support 2" an hour amounts. Given the
sensitive terrain in the area, urban areas, dry washes/arroyos,
burn scars, slot/box canyons, and relatively moist soils, this
setup will likely produce scattered instances of flash flooding. A
broader Marginal Risk area surrounds the Slight and includes
portions of the Great Basin and New Mexico where there will also be
scattered convection, but the flash flood risk will be more
isolated as rainfall rates are less likely to exceed FFGs.

...Southern/Central Plains & Midwest...
Widespread moderate to locally heavy rainfall will continue into
Friday morning across portions of Texas and Oklahoma as a shortwave
moves northeast across the southern and central Plains and
interacts with a returning front. Any lingering convective
activity from Thursday night/early Friday morning could be ongoing
in and near IA at the start of the period. The southern stream jet
should shift north, maintaining favorable conditions for convection
through Friday afternoon. Anomalous moisture will remain in place
across the southern Plains and precipitable water values of 1.25"+
broaden in scale across portions of the Midwest/Corn Belt.  Cloud
cover could limit instability. With favorable dynamics, there
should still be enough support for locally heavy rainfall, up to
1.5" in an hour, which would be most problematic in urban areas.
The flood risk will mainly be a function of duration, with rainfall
impacts compounding from Thursday into Friday. The highest risk of
flash flooding is more likely materialize over portions of
Texas/Oklahoma and in/near IA which have the highest potential for
heavy rains. The flash flood risk will be relatively low, but
enough for isolated to widely scattered instances of flash
flooding and a Marginal Risk of excessive rainfall.

Roth


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt