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

Valid 00Z Mon Sep 13 2021 - 00Z Wed Sep 15 2021

...Tropical Storm Nicholas to threaten the Texas coastline, as well as
southwest Louisiana, with heavy rain and gusty winds beginning as early as
Monday morning...

...Excessive heat found across the Southwest with above average
temperatures located from the Central Plains to the Ohio Valley and
Mid-Atlantic...

...Severe weather possible for portions of the Lower Great Lakes and
Northeast through Monday, as well as the central High Plains this
evening...

Tropical Storm Nicholas officially formed in the Bay of Campeche earlier
this morning and is forecast to continue moving north-northwest over the
next couple of days and eventually approach the western Gulf Coast. As it
does so, heavy rain ahead of the system may lead to isolated instances of
flash flooding between southern Louisiana and much of the Texas coastline
this evening. As Nicholas draws closer to southern Texas on Monday,
additional round of heavy rain and increasing winds are forecast across
the lower and middle Texas Coast. By Tuesday, impacts are expected to
expand into the upper Texas Coast and southwest Louisiana. Upwards of 20
inches of rain is possible across parts of the Texas coastline through the
middle of the week, with widespread amounts between southern Texas and
southwest Louisiana around 5 to 10 inches. Rainfall amounts of this
magnitude will likely lead to areas of flash flooding, with considerable
flash flood events possible. To highlight the concern, a Moderate Risk
(level 3/4) of excessive rainfall has been issued for Monday and Tuesday
between the lower Texas Coast and southwest Louisiana.

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 through Tuesday. Excessive Heat Warnings remains in place for
parts of southwest Arizona and the Lower Colorado River Valley for both
today and Monday as highs reach close to 110F. 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 Northern Rockies 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 (level 2/5) of
severe weather currently depicted for this evening across southern New
York and eastern Michigan, with a Slight Risk also in effect for Monday
from northern Pennsylvania to northern New Jersey. The potential for
severe weather is also highlighted in eastern Colorado through early
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.

Snell

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