Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Fri Oct 30 2026
Day 3
Valid 12Z Sun Nov 01 2026 - 12Z Mon Nov 02 2026

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

20z Update:

Southwest:Another high end flooding event looks likely across the
Four Corners region as a Pacific storm system and accompanied
atmospheric river will bring widespread heavy rainfall on Sunday.
Model QPF generally showed a maxima of 2-4 inches across the
Mogollon Rim in Arizona and across the San Juan mountain range in
southwestern Colorado.Additionally,guidance had signals of 5, 10,
and isolated 25 year ARI QPF across these zones. This is a good
indicator of higher end flash flooding impacts historically.
Moreover, the area is extremely saturated from prior rounds of
rainfall with high creeks and streams. Accordingly, a Moderate Risk
was added across the Mogollon rim of south, central Arizona
northward into the canyons of southern Utah. Urbanized centers,
burn scars, and slot canyons will be the most vulnerable to flash
flooding. A SLight Risk extends outside these zones across the Four
Corners where flash flooding impacts are expected on a more
scattered nature. Southern California remains in a Marginal Risk
where isolated flash flooding concerns are possible as the AR
glimpses their area.

Florida: A Slight Risk was added along the east coast from
Melbourne southwards to Miami. Afternoon guidance had relatively
good agreement of a swath of 2-3 inches across the Florida
Peninsula on Sunday. A shortwave trough will dig southwards across
the eastern Gulf and move into Florida. Upper and mid-level forcing
from this wave will interact with a tropical air mass and PWATS
over 2 inches to produce locally heavy rainfall. The Slight Risk
kept along the east coast of Florida where saturated soils and
greater urbanization could increase the flash flood threat to a
level 2/4 risk.

Wilder

...Previous Discussion...

...Southwest...

A high-impact heavy rainfall event is likely to unfold across the
Four Corners region on Sunday. Abundant moisture to 4-5 sigma above
normal will move northeast ahead of a deep and vigorous longwave
trough over the West. As that moisture runs into the 14,000 ft
peaks of the San Juans of southwest Colorado, it will very
effectively be wrung out by the terrain as that moisture uplifts
across the mountains. This will make for an 18 hour or so period of
steady heavy precipitation across those ranges. The San Juans will
be particularly targeted with heavy precipitation due to the tall
peaks of many of the mountains that are aligned perpendicular to
the mean southwesterly flow. Snow levels will rise above 11k feet,
meaning only the highest peaks will see significant snowfall.
Meanwhile the mid-mountains down to the valleys will all see heavy
rain, that will be quickly funneled into the headwaters of the San
Juan river. In a near-repeat of last week's heavy rain event, the
still saturated soils will quickly convert nearly all of the rain
into runoff, resulting in fast and steep rises along area streams
and creeks as well as the larger San Juan river.

The Moderate Risk was hoisted with this update due not only to the
very favorable meteorological and hydrologic conditions for flash
flooding, but also for the very short period of time in between
this area's big rainfall events. The Moderate was coordinated with
the ABQ/Albuquerque, NM forecast office.

Elsewhere across the Southwest, a large Slight covers all of
Arizona and portions of each of the neighboring states. Much of
Arizona is in a higher-end Slight as the flood prone deserts and
numerous canyons will also effectively funnel the heavy rains into
small and fast-reacting river basins. Much like in the San Juans,
back-to-back major rainfall events could have outsized impacts
across Arizona. While the Mogollon Rim area is generally able ot
handle heavier rains as compared with the other topography,
multiple days of heavy rain could lead to more widespread flooding
impacts. It remains possible that another Moderate Risk upgrade may
be needed for portions of this area, particularly in central
Arizona.

...Florida...

A vigorous tropical wave tracking east across the Gulf will impact
the Florida Peninsula on Sunday. A notable increase in instability
will accompany PWATs over 2 inches in some areas. Unlike previous
days where the heaviest rains were confined to the immediate east
coast, on Sunday essentially all of the Florida Peninsula will see
over an inch, and in many areas over 2 inches of rain. Areas such
as the Treasure Coast already have saturated soils, and will be
much more prone to developing flooding as compared to much of the
west coast of Florida. Nonetheless, given the abundant moisture and
weak flow that will keep any storm motions slow, all of the
Peninsula will at least have an isolated risk of flash flooding. A
Slight Risk upgrade is probable with future updates, especially
around the Treasure Coast, once the CAMs guidance can add more
detail to the forecast.

...Elsewhere...

The Marginal Risk for the lower Tennessee and Ohio Valleys follows
ongoing rain from Saturday night continuing into Sunday morning in
the form of slow-moving convection. With daytime heating, this too
should weaken with time. Across the central Plains, the flooding
threat will come Sunday night as the heavy rains with the storm
impacting the Southwest during the day eject east into the Plains.

Wegman

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