Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
851 PM EDT Sat Aug 22 2026
Day 2
Valid 12Z Sun Aug 23 2026 - 12Z Mon Aug 24 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
CENTRAL US AND THE SOUTHWEST...

...2030Z Update...

A Marginal Risk was added along the shores of Lake Erie from
northeastern Ohio into western New York due to expected lake-
enhanced showers after an initial round of locally heavy rainfall
today. The 12Z CAM guidance now available through the full day 2
period shows the potential for isolated occurrences of 2-4" of
additional rainfall, especially for northwestern Pennsylvania and
into western New York.

Elsewhere, some modest areal modifications were needed across
portions of the Plains to the Lower Mississippi Valley for
northwesterly flow storms and with Monsoonal activity over the
western U.S. Two main genesis locations were noted in the Plains
portions of the outlook: the first to the north over the Dakotas
and the second to the south over Kansas/Oklahoma southeast through
the Ozarks and into the Lower Mississippi Valley. The 12Z CAMs were
more aggressive with storm coverage/rainfall amounts with the
storms developing over the Dakotas and then progressing southeast
into the Missouri Valley, likely due to support from a more
prominent shortwave and developing low level jet into the overnight
hours. Some of the CAMs show the potential for locally heavy
totals in the 2-4"+ range which could result in more than just a
few isolated instances of flash flooding. However, due to the
expected progressive nature of the storms as well as uncertainty
with the degree to which they organize/grow upscale and eventually
track, have maintained a Marginal Risk for now.

Putnam

...Previous Discussion...

...Midwest...

Energy approaching from the west begins to flatten the northern
portion of the ridge...allowing for showers and thunderstorms to
develop across the northern Plains which then builds southeastward
towards the Ozarks. Even though flow aloft is from the
northwest...the 850 mb flow maintains a plume of precipitable water
values in excess of 1.75 inches from the Gulf coast northward into
the eastern Dakota which roughly defines the ridge in the thetae
field to help fuel locally heavy rainfall rates. And given the
potential for repeat convection...maintained the Marginal risk
area even though individual cells should remain progressive.

...Western US...

The overall pattern is expected to remain relatively unchanged
with the upper ridge remained anchored over the Southwest and
southern Plains. Moisture and energy moving along the western and
northern periphery of the ridge will contribute to daily shower and
thunderstorm activity and the potential for isolated flash
flooding extending from the Southwest to the northern Intermountain
West and Rockies.

Bann


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