Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
546 AM EDT Sat Aug 29 2026
Day 2
Valid 12Z Sun Aug 30 2026 - 12Z Mon Aug 31 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
ARIZONA AND SOUTHERN UTAH...

...Southwest/Great Basin/Intermountain West...

A persistent Monsoon environment characterized by PWATS in the
1.5-1.75 inch range and CAPE around 1000-1500 J/Kg, as well as
increasing synoptic support as an upper-trough enters the
Southwest, will support increasing thunderstorm coverage and
periods of heavy rainfall from Arizona to southern Utah. During
this time portions of Arizona and southern Utah will have
increasing coverage of showers and thunderstorms and thus have a
Slight Risk for excessive rainfall in effect.

Elsewhere, a Marginal Risk of excessive rainfall remains for above
average moisture fueling diurnally driven widely scattered
convection across portions of the Rockies, and parts of the Great
Basin. The degree of moisture expected could lead to hourly rain
amounts to 2" wherever cells sit, merge, or train. This could lead
to isolated flash flooding...with favored terrain, urbanized areas,
box/slot canyons, arroyos/dry washes, and burn scars being the
most prone to flooding.

..Southeast...

During this period an upper level disturbance will be retrograding
near the central Gulf in proximity to a dying frontal boundary. With
precipitable water values of 2"+ expected, hourly rain amounts to
3" are possible where cells merge or train, thus maintaining an
elevated threat for isolated flash flooding. The Marginal Risk was
maintained across the Gulf Coast/Southeast.

...Upper Midwest/Northern Plains/Great Lakes...

Upper level ridge axis will continue to shift to the east during
this period which will increase monsoonal moisture reaching to the
Plains and Midwest. Precipitable water values are expected to be
in the 1.5-2" range. Where cells train or merge, hourly rain
amounts to 2.5" are possible. Marginal Risk areas remain in
effect.

Campbell


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