Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Tue Sep 21 2021

Valid 00Z Wed Sep 22 2021 - 00Z Fri Sep 24 2021

...Slow-moving cold front to bring heavy rain and unseasonably cool
temperatures to portions of the Great Lakes, Ohio and Tennessee Valleys,
and Mid-Atlantic through Thursday...

...Heavy rain also likely from the coastal Carolinas to the southern
Appalachians Tuesday...

...Elevated risk of fire weather conditions expected in northern Texas on
Tuesday, the Central Great Basin and Northern Plains on Wednesday...

A strong cold front extending from the Great Lakes through the Lower
Mississippi Valley will continue its slow eastward progression today,
pushed ahead by a broad area of surface high pressure settling in over the
Great Plains. Showers and thunderstorms are forecast to develop along the
length of the front, with isolated damaging wind gusts possible from
eastern Texas to southeast Arkansas/northwest Mississippi. The heaviest
rainfall is expected along the front axis from eastern Michigan through
central Tennessee, which has been denoted to be at a Slight Risk for
Excessive Rainfall by the Weather Prediction Center through tomorrow
morning. Fueled by an amplifying upper-level trough and above normal
atmospheric moisture, widespread rainfall accumulations of 2", with
isolated higher amounts in the 4-6" range, will be possible and may cause
scattered flash flooding.

By Wednesday morning a low pressure center that had been tracking north
along the front is forecast to remain quasi-stationary over Ohio as it
deepens throughout the day, facilitating the development of breezy
conditions around the closed surface low. As the trailing cold front moves
into the Southeast and Mid-Atlantic, the potential for heavy rain and
isolated damaging wind gusts will follow. Shortwave energy at the surface
will allow for additional heavy rain to fall over the Lower Great Lakes,
while showers and thunderstorms along the cold front will produce heavy
rainfall totals upwards of 3", with isolated pockets of up to 6", from the
Blue Ridge Mountains through western/central Pennsylvania. To account for
flooding potential over the already saturated soils in the Ohio Valley and
the new, very heavy rainfall over the Mid-Atlantic the Weather Prediction
Center has issued two upgraded Moderate Risk areas for Excessive Rainfall
for the aforementioned regions valid from Wednesday morning through
Thursday morning. Heavy rain is expected to continue on Thursday as the
cold front passes through the remainder of the Mid-Atlantic and approaches
New England Thursday evening. Though rainfall totals are forecast to be
lower than the previous two days, more rain on top of the already
saturated soils could cause scattered flash flooding to occur,
particularly in eastern Pennsylvania.

In addition to producing widespread heavy rainfall, the cold front is
expected to bring unseasonably cool temperatures to the areas it passes
through. On Wednesday, daily highs in Michigan, the Ohio Valley and upper
Tennessee Valley are forecast to be 10 to 20 degrees below normal, with
high temperatures failing to reach 65 degrees in southern Michigan,
Indiana, Kentucky, and western Ohio. Temperature departures of 10 to 15
degrees will continue for southern Michigan and the Ohio Valley on
Thursday, with daily highs primarily in the low to mid 60s.

To the east of the cold front, onshore winds are advecting moisture ahead
of a quasi-stationary boundary to the coastal Carolinas. Energy from an
upper-level shortwave trough working in tandem with surface instability
will support heavy rain up to and exceeding 2" from the coastline to the
southern Blue Ridge Mountains. To account for the possibility of local to
scattered flash flooding, the Weather Prediction Center has issued a
Slight Risk for Excessive Rainfall for these regions through tomorrow
morning.

The Storm Prediction Center has forecast an elevated risk of fire weather
for northern Texas today due to the aforementioned cold front advecting
dry air into the region while producing breezy conditions. Tomorrow this
elevated risk will shift to the Central Great Basin and Northern Plains,
where downsloping winds, low relative humidity, and dry fuels could be
receptive to fire spread.

Out west, strong surface high pressure will allow dry conditions to
persist from the coast to the Great Plains throughout the short-range
period. Additionally, marginal to moderately above normal temperatures are
expected for much of the western-half of the country on both Wednesday and
Thursday.

Zavadoff

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