Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1133 AM EDT Sun Sep 27 2026
Day 2
Valid 12Z Mon Sep 28 2026 - 12Z Tue Sep 29 2026

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

...Southwest/Four Corners...
A predecessor rainfall event (PRE) is likely to impact much of the
region beginning by midday and continue into the end of the
period. Moisture preceding the arrival of the primary moisture
plume associated with Hurricane Polo will continue to spread across
the region as it is drawn northeastward ahead of a mid-to-upper
level low digging south across California toward the lower Colorado
Basin.

As PWs increase to 2-3.5 std dev above normal across much of the
region, strong upper level divergence combined with amplified
southwesterly flow orthogonal to the terrain will support
significant synoptic and orographic forcing.

A limiting factor will be instability, hampered by thick cloud
cover and shortening daylight. However, the strong forcing and
anomalous moisture is likely to support very efficient warm-rain
processes that will compensate for the limited CAPE.

A broad Moderate Risk remains in place -- covering the complex
terrain and burn scars of southern Utah, southwestern Colorado, as
well as much of northern and central Arizona and New Mexico. One
smaller adjustment this issuance was to extend the Moderate Risk a
bit farther southeast into the extremely vulnerable areas of
southeastern New Mexico, where soils remain nearly saturated from
recent rounds of heavy rain.

...Dakotas/Northwestern Minnesota...
Coupled upper jet forcing along with deepening moisture (PWs ~1.5
inches) on the nose of a southerly low level jet will promote
training showers and storms across portions of the eastern Dakotas
into northwestern Minnesota. A Slight Risk was maintained from
northeastern North Dakota into northwestern Minnesota, where
there remains a good model signal for widespread totals of 1-2
inches, with locally heavier totals.

Pereira


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