Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Mar 01 2021

Valid 00Z Tue Mar 02 2021 - 00Z Thu Mar 04 2021

...Rain and thunderstorms will develop across the Gulf Coast states
through Wednesday...

...Light snow and gusty winds are expected in the Great Lakes to Northeast
through Tuesday...

A quasi-stationary front extending across the Gulf Coast will have a
low-pressure wave moving eastward from the Western Gulf Coast to off the
Southeast Coast by Wednesday. Moisture from the Gulf of Mexico will move
northward over the boundary, producing rain and thunderstorms along the
Gulf Coast into the Southeast through Wednesday. The rain will slowly end
from the Western Gulf Coast to the Southeast during this time period. A
second front extending from the Northeast/Mid-Atlantic to the Middle
Mississippi Valley will move off the East Coast by Tuesday morning. The
associated surface low over Eastern Canada will deepen rapidly, producing
a tight pressure gradient over the Northeast into the Mid-Atlantic. The
tight pressure gradient will produce a strong gusty wind over the region
through Wednesday. The gusty wind will end from the West to the
Northeast. Light snow will also develop over the Great Lakes to the
Northeast that will wane overnight Monday. A third front will move
southeastward from Central Canada on Tuesday afternoon, advancing to the
Northeast/Mid-Atlantic by Wednesday evening. Light snow will develop over
part of the Northeast on Wednesday into Wednesday evening.

Meanwhile, upper-level energy moves into the Pacific Northwest on early
Tuesday morning and moves eastward to the Northern Plains by Tuesday
night. The energy will produce light snow over parts of the Northern
Cascades and parts of Northern Rockies on Tuesday into Wednesday.
Additionally, an upper-level low will move onshore over Southern
California late Wednesday. The low will help produce light rain over
parts of Southern California on Wednesday afternoon into Wednesday
evening.

Ziegenfelder
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Mar 1 2021

Valid 12Z Thu Mar 4 2021 - 12Z Mon Mar 8 2021

18Z Update: The 12Z model guidance, along with the 00Z ECMWF, are
in above average agreement on the synoptic scale pattern through
Friday across the continental U.S., and a general deterministic
model blend sufficed as a starting point in the forecast process.
By Saturday, the operational GFS becomes notably more progressive
with the shortwave crossing the Intermountain West compared to the
other guidance, including the GFS parallel, and the 12Z CMC
trended more in line with the slower ECMWF, although not as slow
as its 00Z run. Since the GFS parallel version was closer to the
ensemble means, it was given more weighting for the second half of
this forecast period than the regular GFS, and more contributions
from the EC and GEFS means by next Monday. In terms of sensible
weather, the heaviest precipitation appears most likely for
portions of the Pacific Northwest early in the forecast period,
and rainfall chances increase for the Florida Peninsula for this
weekend as the Gulf of Mexico low affects the region. This low is
expected to track far enough offshore to keep most of the East
Coast region dry, but if future forecasts trend more towards the
northwest, then precipitation chances could increase for coastal
regions. The previous discussion is appended below for reference.
/Hamrick

...Overview and Guidance Evaluation...

Latest models and means continue to show a fairly amplified large
scale upper pattern featuring a west-central U.S./Plains ridge
between mean troughs over the eastern Pacific and East Coast.
Embedded within this pattern will be an upper low that should
reach the southwestern U.S. and then the Southern Plains after
midweek, followed by rather pronounced suppression of the upper
energy and surface reflection beneath the eastern mean trough
aloft. The axis of this trough should be far enough eastward to
keep any developing Atlantic low pressure by the weekend/early
next week well offshore. The eastern Pacific mean trough will
feature two primary features, one likely reaching the West Coast
early in the weekend (with leading wavy front) and then ejecting
inland followed by amplifying upstream energy that should bring
another system toward the Northwest toward late weekend/early next
week.

Guidance has stabilized since runs from 24 hours ago had adjusted
slower for the upper low tracking into the southwestern U.S. and
Southern Plains, followed by suppression of most moisture/surface
waviness around the southern periphery of high pressure that
builds over parts of the east-central/eastern U.S. and Southern
Plains. Hopefully this evolution represents something close to a
"final answer" after multiple days of wildly diverse and
inconsistent solutions, first for whether an upper low would form
to begin with and then the low's track/timing.

The primary forecast discrepancy upstream regards how the leading
trough off the West Coast ejects inland after guidance maintains
good consensus into Friday. Thus far there have generally been
two persistent clusters, a slower/sharper ECMWF-led majority that
ultimately brings the remaining shortwave energy
eastward/east-northeastward as it continues across the lower 48,
and the faster/flatter GFS-GEFS mean that take more of the energy
around the ridge. CMC runs through 12Z have been somewhat of a
compromise. A blended approach still looks reasonable, leaning
two-thirds or so toward the majority cluster near the West Coast
into Saturday while toning down the strength of this energy
relative to the 12Z ECMWF as it continues into the large scale
mean ridge. The 00Z GFS/GEFS mean have adjusted a little slower
than their prior runs, the CMC has adjusted close to the ECMWF
idea, and the new ECMWF has become less amplified as the energy
ejects inland--in sum maintaining general support for current
preferences. The next system that reloads the East Pacific mean
trough aloft shows fairly good large scale agreement in most
models and means (00Z CMC could be somewhat flat). Thus a
model/ensemble mean composite represents the large scale pattern
well while downplaying low-predictability details during the
latter part of the forecast.


...Weather/Threats Highlights...

The upper low likely to reach the Southwest/Great Basin area by
early Thursday will produce locally enhanced rain and higher
elevation snow over the Four Corners states with moisture then
extending eastward into the Plains. Some moderate to heavy
rainfall is possible over the Plains but likely over a fairly
small area. Then most of the rainfall should trend lighter as it
gets suppressed along and south of the Gulf Coast, though activity
could rebound again over parts of the Florida Peninsula during the
weekend. Continue to expect any low pressure development over the
western Atlantic from the weekend into early next week to be well
offshore. From late week into the weekend the eastern Great Lakes
could see some lake effect activity in prevailing cool cyclonic
flow.

Precipitation associated with the first eastern Pacific upper
trough/surface front will focus primarily over Vancouver Island
and into the Olympics at first and then extend southward toward
the central West Coast and possibly farther south over California.
A frontal wave nearing the coast may support a band of heavier
precipitation by Saturday. Rain and mountain snow will trend
lighter as the upper shortwave continues inland, with mostly light
totals over the Interior West and Rockies. The next system should
bring another episode of rain and mountain snow to the northern
half or two-thirds of the West Coast.

Expect temperatures over the Northern Plains and vicinity to
remain well above normal through the period with plus 10-25F
anomalies for highs and only slightly less extreme for morning
lows. The amplified pattern aloft will also bring a more moderate
warming trend to the West including warmest anomalies of plus
10-15F for highs from portions of the Interior West into the
Southwest and eventually southern Rockies. Meanwhile the upper
trough near the East Coast will keep that part of the country on
the chilly side. Highs of 5-15F below normal are likely to be
most widespread Friday-Sunday.

Rausch