Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
250 AM EDT Fri Mar 15 2024

Valid 12Z Mon Mar 18 2024 - 12Z Fri Mar 22 2024

...General Overview...

An amplified upper level pattern is expected to be in place across
the continental U.S. for the beginning of next week, featuring a
deep upper trough across the Great Lakes/Ohio Valley region, and a
Rex block over the Western U.S. with a closed upper high over the
Pacific Northwest and a loitering upper low over the Desert
Southwest. The trough over the East slowly lifts out some by
midweek, and the southwest upper low evolves into an open wave and
then ejects eastward across the Southern Plains going into
Thursday. A more zonal flow pattern aloft is likely by the end of
the week, although a developing low pressure system over the
south-central U.S. will increase the prospects for showers and
storms for the Gulf Coast and the Deep South/Southern Plains.

...Guidance/Predictability Assessment...

The 00Z guidance suite remains in reasonable agreement with the
flow pattern into early next week, with some uncertainty in the
details and timing of individual shortwaves across the Eastern U.S.
within the larger scale upper trough. At the time of
fronts/pressures composition, the CMC differed the most from the
model consensus across the northeastern quadrant of the nation with
timing and amplitude of individual shortwaves. Later in the
forecast period, the GFS is more progressive in ejecting the upper
low/shortwave from the Desert Southwest to the Southern Plains, but
has enough ensemble support to seem like a reasonable scenario.

The WPC forecast incorporated a general deterministic model blend
for Monday and Tuesday, with more weighting applied to the GFS and
ECMWF. After that, there was a gradual increase in the use of the
ensemble means to about 50 percent of the blend by Friday, along
with the GFS and ECMWF and some previous WPC continuity through
Thursday.

...Weather/Hazards Highlights...

After multiple days of heavy rainfall in the short range forecast
period, there will likely be a welcomed abatement in both rainfall
coverage and intensity going into early next week. The front
crossing central Florida on Monday will probably produce some
moderate to locally heavy rainfall in places, but not enough to
warrant any Marginal Risk areas at this time. The same holds true
for the Rio Grande region of southwestern Texas with southerly flow
ahead of the ejecting southwest U.S. upper low with mainly light to
moderate rain expected. An even quieter pattern is likely on
Tuesday for the Day 5 period with no risk areas necessary.

To the north, a secondary cold front crossing the Great
Lakes/Northeast should bring some generally light precipitation
across the region. Sufficient cold air and low level moisture may
combine to produce some accumulating snows for portions of the
central Appalachians and downstream of Lake Erie and Lake Ontario.
Looking ahead to Wednesday into Thursday, showers and thunderstorms
will likely increase across the Gulf Coast region into the Deep
South and eastern Texas as Gulf moisture advects northward ahead of
a developing surface low, with the greatest rainfall near the
coast and offshore. Snow will likely make a return to the northern
Rockies late in the week as well.

Temperatures from the Midwest to the East Coast are forecast to be
5 to 15 degrees below average on Monday and Tuesday as a Canadian
surface high will be in place. There will likely be some
frost/freeze concerns for any areas where spring green-up has
started as temperatures dip well into the 30s to near freezing,
especially Tuesday morning. Temperatures across the Southwest will
trend warmer with time as the upper low weakens, and above normal
temperatures expanding over the Northwest early in the week will
move into the northern/central Plains and Upper Midwest by next
Wednesday, and colder weather arrives to Montana and North Dakota
by the end of the week.

Hamrick