Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1152 AM EDT Sat Sep 5 2026
Day 2
Valid 12Z Sun Sep 06 2026 - 12Z Mon Sep 07 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHERN
NEVADA AND NORTHWESTERN ARIZONA TO CENTRAL UTAH AND OVER PORTIONS
OF SOUTH CAROLINA AND GEORGIA...

...Western U.S....
An upper low centered along the Pacific Northwest coast early in
the period is expected move inland, reaching the northern
Intermountain West by the close of the period. Meanwhile, a series
of shortwaves moving along the base of the associated trough will
track across southern California before lifting northeast through
the Great Basin. In addition to this energy, southwesterly flow
will tap tropical moisture associated with Maria, supporting an
impressive PW anomaly axis (+3 std dev) extending from southern
California to central Utah. This moisture along with large-scale
ascent afforded by the aforementioned shortwaves and upper jet
forcing is expected to set the stage for widespread shower and
thunderstorm activity. However, limited instability remains a
potentially factor with regards to rainfall rates. A Slight Risk
remains where models continue to signal where moisture, lift, along
with orographic effects will support an enhanced threat for
heavier amounts. Only minor adjustments were made to the previous
Slight Risk area extending from southern Nevada and northwestern
Arizona to central Utah, including a small shift to the north that
reflects the latest trend in the guidance. Remaining in this area
are some of the more flash flood prone areas in southwestern Utah.

Farther east, more typical monsoon moisture will support diurnal
activity, with the potential for isolated flash flooding across
southeastern Arizona, New Mexico, and southern Colorado.

Elsewhere, a broad Marginal Risk was maintained to the north,
covering portions of the Northwest, northern Rockies, and High
Plains. The previously noted upper low/trough is expected to
support widespread activity. Instability west of the Rockies will
remain quite limited, however rates may become sufficient to raise
isolated concerns, especially across recent burn scars.

...Northern Plains to the lower Missouri Valley...
While the models are showing plenty of differences in the details,
there is a growing signal for heavy amounts impacting at least a
portion of the area as energy spills off of the top of a
persistent ridge centered over the Plains. This energy is forecast
to interact with a strengthening low level jet and axis of
deepening moisture (PWs ~1.75 inches). There is indication in some
of the models, including the ARW, NAM, and RGEM, that heavy rains
may be ongoing or developing near the start of the period across
portions of the eastern Dakotas and western Minnesota. This
activity will eventually drop south, followed by additional storms
developing late in the period and possibly impacting some of the
same areas. Model spread did not offer enough confidence to go
higher than a Marginal Risk. However, this is an area where a
potential upgrade may be necessary, especially if the hi-res
guidance begins to show a more unified signal.

...Southeast...
Energy dropping into the base of a broader-scale trough centered
along the East Coast is expected to support a weak wave developing
along a slow-moving, moisture-laden front extending from the coast
near the South Carolina-Georgia border back across the Southeast.
Models continue to signal heavy amounts near the coast, but also
some potential for heavy rains and potential flash flooding
extending as far north as Upstate South Carolina and western North
Carolina as deep moisture is drawn northwest by the developing
wave. Reflecting the overnight model trends, the Slight Risk was
shifted a little farther south, but also extended northwest along
the South Carolina-Georgia border.

Pereira


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