Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
856 PM EDT Sun Oct 11 2026
Day 1
Valid 01Z Mon Oct 12 2026 - 12Z Mon Oct 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE
GREAT BASIN & SOUTHWEST...


..Great Basin and Southwest...
Post-T.C. Rachel was quite findable in the surface observations,
moving through southwest WY near Big Piney at 00z, headed towards
Jackson Hole and Dubois. Continued very favorable right entrance
region jet dynamics over the Great Basin combined with the moisture
Rachel has left behind and a couple possible zones of frontogenesis
is expected to keep some convection percolating overnight. CIN has
yet to develop, and may not for a while considering how much
moisture exists regionally (precipitable water values of 0.75-1"
across the Great Basin and southern AZ). Due to the reduction in
expected convective coverage, the Moderate Risk was dropped. The
highest risk going forward appears to be across western AZ where
both the 18z HREF and 12z REFS keep heavy rainfall most persistent
overnight -- penciled the area in as an enhanced Slight Risk. Kept
a broad Slight Risk from northwest AZ across portions of the Great
Basin as a course of least regret, to account for any recent
saturation. The usual spots -- burn scars, box/slot canyons, dry
washes/arroyos, and urban areas -- would see the greatest impact
wherever heavy rainfall persisted for an hour or more.


...Mid-Atlantic...
Isaias' surface low is no more; it could not escape WV. It
elongated into a surface trough, absorbed by a downstream cyclone
formation on the other side of the CAD/wedge which at 00z lies
across southern VA. The new cyclone is forecast to move east and
could produce some moderate to heavy precipitation overnight where
precipitable water values remains 1.5"+ and MU CAPE remains in the
500-1000 J/kg range. It may take until 12z Monday for the heavy
rainfall to depart the Eastern/Jersey Shores, though the heavy rain
threat is expected to steadily reduce from here on out. Removed
the Slight Risk but kept a Marginal Risk for what appears to be a
more localized heavy rain threat.

Roth


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