Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Wed Sep 29 2021

Valid 12Z Wed Sep 29 2021 - 12Z Fri Oct 01 2021

...Heavy rain and the threat of isolated flash flooding found across parts
of the Central Plains, Lower Mississippi Valley, and Texas Gulf Coast
today before the bulk of the activity shifts into the Southern Plains on
Thursday...

...Well above average temperatures continue across the Midwest as cooler
air infiltrates the western half of the country and Northeast...

A majority of the active and potentially hazardous weather to end the
month of September will be found across the central and south-central
United States. A deep upper-level trough and associated cold front are
currently swinging across the Rockies, with showers and high elevation
light snow found in its wake. Ahead of the cold front and throughout the
central and southern Plains, a warm and moist airmass in place will allow
for numerous clusters of showers and thunderstorms to develop over the
next few days. For today, most of the thunderstorm activity is expected to
form across the Central Plains as the cold front advances into the region,
as well as farther south along the western Gulf Coast and Lower
Mississippi Valley associated with rich moisture ushering in from the
western Gulf of Mexico. These storms over both regions are likely to be
relatively slow-moving, with flash flooding the main concern. A Marginal
Risk (level 1/4) of excessive rainfall has been issued through Thursday
morning and includes the aforementioned areas. A few severe thunderstorms
capable of damaging wind gusts and large hail are also not out of the
question from south-central Oklahoma to central Texas. By Thursday the
cold front is forecast to reach the southern High Plains and clash with a
tropical airmass in place across the region. This will result in
widespread thunderstorms and locally heavy rainfall. Once again, flash
flooding will be the main concern as numerous clusters of thunderstorms
chaotically interact and potentially occur over similar locations. Thus, a
Slight Risk (level 2/4) of excessive rainfall has been issued over parts
of central and West Texas, with a broad Marginal Risk extending into the
Central Plains and Southern Rockies.

At the apex of an upper-level ridge, warm temperatures around 20 to 25
degrees above average will be found across the Upper Midwest. The warm and
summer-like weather will also be found across a majority of the Midwest
today while only cooling slightly on Thursday. Highs are forecast to reach
the mid-to-upper 80s here. Elsewhere, much cooler and below average
temperatures will be situated over the western U.S. behind a potent cold
front. In fact, Freeze Warnings and Frost Advisories are in effect this
morning across parts of Idaho, Oregon, and northern California. The next
storm system to impact the Northwest by early Thursday will keep
temperatures on the cool side as well, while also dumping several inches
of rain across the Olympic Peninsula and northern Cascades. Meanwhile,
scattered showers and cool temperatures can be expected throughout the
Northeast as an upper-level low is set to meander over the region.

Snell


Graphics are available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php