Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Fri Oct 30 2026
Day 1
Valid 01Z Sat Oct 31 2026 - 12Z Sat Oct 31 2026

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

01Z Update...

The Southwest remains the main focus for ingredients supporting
heavy to potentially excessive rainfall into the overnight hours.
The potential for flooding will gradually wane as the instability
fades. Until then, the ensemble guidance and deterministic QPF
still suggests an additional 1+ inch possible before the available
instability is exhausted. HREF probabilities of exceedance of 1-
and 3-hour flash flood guidance decreases rapidly after
06Z.

Farther east...the rainfall tended to be more stratiform with
embedded convective elements. Given antecedent conditions...was
not inclined to remove the outlook areas.

Bann

..16z Update..

Southwest: The forecast remains on track for a higher end Slight
Risk across south, central Arizona focused around the Mogollon Rim.
There is reasonably good agreement of 2-3 inches of rainfall
across this region with the latest model guidance. HREF
probabilities of 3 and 6 hour QPF exceeding flash flood guidance
peaks around 40-60% in the late afternoon across this region. The
Slight Risk was also extended northward into more of southern Utah
and eastward to encompass more of Nevada, but remains outside the
Las Vegas metro. This expansion correlates well with EAS 24 hr QPF
exceeding 2 inches, as well as covering latest 20-40% probabilities
of 3hr and 6hr QPF exceeding flash flood guidance. Urban areas and
sensitive terrain such as burn scars and slot canyons will be the
most likely to see impacts from flash flooding.

Southern to Central Plains: A shield of moderate rainfall
continues across much of Texas this morning/early afternoon with
hourly rainfall rates generally half an inch of less. Despite the
modest rainfall rates, additional rainfall over saturated soils
from yesterday's rainfall will maintain a continued isolated flash
flood threat. Low water crossings across the Hill Country will be
the most susceptible to flooding concerns, where flash flood
warnings were issued this morning. Moisture will continue to stream
northward through the central Plains where 1-2 inches of rainfall
may accumulate through the day. Relatively high flash flood
guidance should keep any flooding, if it occurs, isolated. The one
exception will be across northern Kansas where rainfall overnight
has lowered flash flood guidance to under an inch per hour in some
locations; this area will more susceptible to water runoff
concerns.

Wilder

...Previous Discussion...

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