Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Sun Sep 12 2021

Valid 12Z Sun Sep 12 2021 - 12Z Tue Sep 14 2021

...Developing tropical activity over the Bay of Campeche to produce heavy
rainfall and growing concerns for flash flooding starting late Sunday and
into the first half of next week for the western Gulf Coast including
coastal areas of Texas and Louisiana...

...Stifling heat for mid-September to continue from the Southwest and
Midwest to the Mid-Atlantic...

...Severe weather possible for portions of the central and northern Plains
eastward into the Great Lakes and Northeast...

An area of disturbed weather over the Bay of Campeche has a high
likelihood of developing into a tropical depression later today or Monday
as this disturbance moves northwestward and then northward near the coast
of northeastern Mexico. A surge of tropical moisture associated with this
feature combined with a surface trough extending north across the western
Gulf of Mexico will generate heavy showers and thunderstorms along the
coastal areas of Texas and Louisiana by late Sunday. This activity will
spread gradually farther inland across the western Gulf Coast region
through the first half of the week. Locally significant rainfall totals
are expected, potentially resulting in areas of coastal, flash, and urban
flooding. The slow progress of this system as well as persistent moist
southeasterly flow results in several days worth of heavy rainfall from
the Texas coast to southern Louisiana. This long duration event is evident
in the Weather Prediction Center's Excessive Rainfall Outlooks as three
days worth (Sunday-Monday-Tuesday) of Slight Risks have been issued for
much of the western Gulf Coast. Interests from Brownsville, TX to the
mouth of the Mississippi River should continue to monitor the situation
closely. Please consult the latest National Hurricane Center Tropical
Weather Outlook for more information.

Elsewhere, an expansive dome of upper-level high pressure stretching
across the southern two-thirds of the U.S. mainland allows for abnormally
hot conditions to continue, with the heat encompassing a broad area from
the Southwest and Midwest to the Mid-Atlantic. Temperatures will be as
high as 15 to 20 degrees above normal with the greatest concentration of
these anomalously hot conditions stretching from the central Plains to the
Mid-Atlantic. Record high temps will be challenged locally across the
southern High Plains and Southwest today, followed by parts of the
Mid-Atlantic by Monday. In fact, Excessive Heat Warnings remains in place
for parts of southwest Arizona and the Lower Colorado River Valley for
both today and Monday. Generally the coolest temperatures are likely to be
confined to the Pacific Northwest and the northern Plains in wake of a
pair of cold frontal passages crossing the region.

A cold front crossing the Pacific Northwest and northern Plains will be
associated with an upper-level trough, which is expected to gradually
break down the aforementioned ridge of high pressure over of the southern
two-thirds of the nation by mid-week. As this occurs, an elongated frontal
zone with several waves of low pressure advancing along it will be the
catalyst for scattered areas of heavy showers and thunderstorms. This will
impact a broad area from the central and northern Plains through the
Midwest and into the Northeast. Some localized severe weather is possible
as the Storm Prediction Center does have a Slight Risk of severe weather
currently depicted for Sunday across southern New York, far northern
Pennsylvania, and eastern Michigan. A Slight Risk of severe weather is
also highlighted in eastern Colorado today with a large Marginal Risk area
in the Northern Plains and Midwest on Monday. Severe storms may contain
damaging winds and large hail, along with locally heavy rainfall rates
that may lead to some instances of flash flooding.

Mullinax

Graphics are available at www.wpc.ncep.noaa.gov/basicwx/basicwx ndfd.php