Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
824 PM EDT Sat Oct 31 2026
Day 2
Valid 12Z Sun Nov 01 2026 - 12Z Mon Nov 02 2026

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

21Z Update...
Models remain in good agreement overall with the significant rain
potential in the Southwest. Made only minor modifications based on
the newest 12Z guidance and carved out a bit more snow-only areas
(though there is an implied minimum in the ERO above the snow
level). Did slightly expand the Southeast Marginal into northern
MS/AL based on a shift in the heavier rain probabilities.

Fracasso

The previous (09Z) discussion lies below...

...Southwest...

Two separate Moderate Risk areas were retained with this update for
portions of the Four Corners. The smaller Moderate Risk along the
San Juans of southwest Colorado was left largely unchanged with
this update. An atmospheric river of extremely anomalous moisture
will make its passage across much of the Southwest during the day
Sunday. PWAT values of 3/4 inch to 1.5 inches are anywhere from 4
to 6 sigma above normal, threatening daily records. All of this
moisture will slam first into the Mogollon Rim region, then
continue into the San Juans. The San Juans have recently seen a
high-impact flash flooding event from a similar feature about a
week ago, and soils have not had a chance to dry out due to a
series of smaller rainfall events in the meantime. Now this event
will threaten to rival the first. Thus, the Moderate Risk looks in
very good shape.

More significant changes/expansions were made across Utah with this
update. In coordination with SLC/Salt Lake City, UT forecast
office, the Moderate Risk was expanded north up I-15 to include the
several very large burn scars dotting around the I-15 and I-70
junction. These burn scars have a history of producing flash
flooding due to heavy rainfall, so the outsized impacts that are
expected with the 1-2 inches of rain forecast led to the Moderate
Risk upgrade. In addition, the surrounding Slight Risk was expanded
north to include the Salt Lake City metro area, due to urban
concerns worsening any localized flash flooding from the nearby
mountains. The heaviest rainfall remains across central Arizona and
the Mogollon Rim region. A higher-end Moderate Risk may be needed
given the impacts that have occurred from the lesser rainfall
amounts that have fallen there over the past couple days. Expect
widespread 3 inch totals north and east of Phoenix, with localized
higher amounts. All of this rainfall will convert to runoff due to
already well-saturated soils.

...Central to Northern Plains...

A small Marginal Risk area that was in place across Kansas and
eastern Nebraska was shifted northward with this update with
changing guidance. Soils are around normal for moisture amounts,
which should help to absorb much of the rainfall expected. Further,
a complete lack of instability will hold any rainfall rates down.
Thus, this Marginal is a low-end one and could be dropped entirely
with future updates.

...Southeast...

In coordination with MLB/Melbourne, FL and JAX/Jacksonville, FL
forecast offices, the inherited Slight Risk along the east coast of
FL was expanded north through the Jacksonville metro. A wave of
tropical moisture with PWATs on either side of 2 inches will cross
the Florida Peninsula on Sunday. This will lead to widespread
rainfall all across the Peninsula. The east coast of the state
continues to have saturated soils from numerous consecutive days of
rainfall. Thus, the soils will be unable to absorb much of the
heavy rains expected. This will lead to widely scattered instances
of flooding. Urban and low-lying areas will be particularly
vulnerable.

Meanwhile, across the Ohio and Tennessee Valleys, a lack of
instability and generally light rainfall over parched ground should
limit any flash flooding threat, even if a stray thunderstorm were
to form. The Marginal Risk was trimmed from these areas, and may be
able to be trimmed further to close to the Gulf Coast, where any
and all instability will reside on Sunday.

Wegman


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