FOUS30 KWBC 300826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Fri Oct 30 2026

Day 1
Valid 12Z Fri Oct 30 2026 - 12Z Sat Oct 31 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
ARIZONA, SOUTHERN UTAH, AND SOUTHWESTERN NEW MEXICO...

...Arizona, Utah, New Mexico, Colorado...
Scattered to numerous thunderstorms are expected to develop
primarily across central through eastern Arizona during the
forecast period. Convection could start as early as 15Z before
expanding in coverage an intensity. Many areas of 1.5-3 inch
rainfall totals are expected, with highest totals along the
Mogollon Rim eastward toward the White Mountains. Scattered
convection should also peak during the afternoon across
southeastern Arizona and portions of southwestern Utah. A Slight
Risk has been maintained in much of this region for the new D1
update, with expansions into southeastern Arizona and southwestern
New Mexico to account for scattered convection that should migrate
into these areas especially in the 00-06Z timeframe. Several
instances of flash flooding are possible given this regime, with
typical low spots/slot canyons and other sensitive terrain being
most susceptible to impacts.

Farther northeast, a Marginal Risk has been maintained into the Four
Corners region.  While thermodynamic profiles will likely support a
few convective cells as far northeast as southwestern Colorado
during the afternoon and evening, convective coverage is in question
and is varied in the models.  More consistent signals for locally
heavy precipitation exist in these areas after peak heating hours,
which may temper rain rates a bit due to low-level nocturnal
stabilization processes.  Portions of this region (southeastern UT
into southwestern CO) may need an upgrade to Slight in later updates
if instability (and resultant convective coverage) is greater than
currently forecast -- especially given sensitive ground/riverine
conditions in that area.

...Great Plains...
An ongoing convective cluster in northeastern
KS/northern MO and vicinity should pose a limited/isolated flash
flood risk in the morning hours before gradually weakening due to
decreasing low-level convergence.  Throughout the day, abundant
moisture from a substantial mid-level wave (currently over northern
Mexico) will help spread moderate to locally heavy rainfall through
much of the Plains throughout the day.  A few pockets of deep
convection may develop, though the extent of heavier rainfall will
likely depend on the degree of low-level insolation during peak
heating hours.  Portions of central/southern Texas appear to have a
chance of scattered, slow-moving convection with weakly
supercellular wind profiles in place during the afternoon. Isolated
instances of flash flooding could occur if these heavier rain rates
occur over sensitive/urban locales.  A renewed threat of elevated
convection could pose a risk of isolated flash flooding across
northern Iowa late in the forecast period (06-12Z Saturday morning).

Cook
 

Day 2
Valid 12Z Sat Oct 31 2026 - 12Z Sun Nov 01 2026

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

...Southwest...

A plume of deep tropical moisture will be drawn northeastward by a
longwave positively tilted trough into the Desert Southwest. A
Pacific low at the surface will track towards southern California,
forced by the abundant divergence aloft in the right entrance
region of a 130 kt southwesterly jet. A vigorous shortwave riding
the base of this upper level trough will further enhance lift
supporting heavy rainfall. The jet will allow IVT values to surge
as high as 750 kg/ms. This pattern will advect near record amounts
of moisture for this time of year into the Southwest. PWATs between
1 and 1.5 inches are 4-6 sigma above normal for this time of year.
The result of this highly unusual amount of moisture racing
northeastward will mean the topography of the coastal ranges like
the Peninsular Ranges of southern California and the Mogollon Rim,
which are roughly oriented perpendicular to that southwesterly
flow, will squeeze out ample moisture in the form of heavy rainfall
from the atmosphere.

Expect 1-2 inches of rain along the Mogollon Rim, much of which
occurring after midnight Saturday night. While instability will be
nominal, values will remain high enough to support some elevated
convection, which will occur in addition to heavier rain in the
favored upslope regions. Antecedent soil conditions are also much
wetter than normal, which will support fast developing fast
flooding in flood-prone areas, especially burn scars, dry washes,
slot canyons, and arroyos.

...Lower Mississippi Valley...

Return flow behind an area of high pressure over the Northeast will
draw abundant Gulf moisture northward up the lower Mississippi
Valley into the Ohio Valley on Saturday. While moisture flux and
amounts will be well above normal (2-3 sigma), instability will
also be limited for areas away from the Gulf. Soils in this area
are bone dry, and well below normal for this time of year. Thus,
the Marginal Risk is a low-end one, to cover urban and particularly
flood prone areas.

...Florida...

The Marginal Risk along the east coast of Florida from Cape
Canaveral through Miami is unchanged with this update. Portions of
the Treasure Coast have soils that are water-logged from multiple
days of rainfall. However, as on previous days, robust convection
will struggle to make it too far inland before falling apart, so
the flooding threat remains confined to urban and coastal areas
where soils remain near saturation.

Wegman
 

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...

...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
$$
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