Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Sat Sep 26 2026
Day 3
Valid 12Z Mon Sep 28 2026 - 12Z Tue Sep 29 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FOUR
CORNERS REGION...

...Southwest, Southern Rockies, and adjacent High Plains...

There will be a strong influx of tropical moisture from tropical
cyclones Odalys and Polo directed into the Desert Southwest. This
abundant moisture when coupled with the afternoon diurnal
instability max will trigger scattered to widespread convection
across the region. An interaction between the eventual closed upper
low over California and what will be Polo as it begins moving
northward towards Baja over the course of the weekend into early
next week.

The ensemble means for this time period continue to depict a broad
expanse of heavier rainfall increasingly likely for the Southwest
/Four Corners area due to the ascent pattern downstream of the
upper low swinging into the region. PW anomalies during this period
will be between 2-3.5 standard deviations above seasonal normal
for late September. A broad Slight Risk for excessive rainfall and
flash flooding remains in effect while a higher-end Slight Risk
was raised for east-central Arizona and western New Mexico.,

...Northern and Central Plains...

Progressive northern stream trough coupled with prevalent moisture
advection from the Southwest will lead to a period of convective
concerns and isolated flash flood potential. There is a broad
Marginal Risk in effect from northern Kansas to North
Dakota/northwest Minnesota. Remnant energy from what is currently
tropical cyclone Odalys will get drawn northeastward out of the
Pacific prior to the period reaching the Northern and Central
Plains Monday into early Tuesday leading to quite a larger coverage
of convection over the above area. Areal coverage of convection
will increase Tuesday as there will be a stronger PW surge with the
remnant energy from Odalys. Mean QPF is currently between 1-2.5
inches with locally higher at 5-day leads, a testament to the
threat in question as there will likely be more significant
rainfall potential with this setup.

...New England...

Lingering rainfall expected as the coastal low begins to drift
away from the region. The cumulative effect of rainfall over the
long period into the urban corridor of eastern Massachusetts will
cause hydrologic concerns, including some flooding in poor drainage
locations. A Marginal Risk area is in effect from eastern
Connecticut up to coast to southern Maine.

Campbell/Santorelli

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt