Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Sat Feb 26 2022
Valid 12Z Tue Mar 01 2022 - 12Z Sat Mar 05 2022
...Overview...
Latest guidance continues to show an upper pattern consisting of a
western ridge and broad eastern mean trough through midweek,
followed by a transition toward a mean trough settling into the
western U.S. while upper heights rise farther to the east. The
primary precipitation focus early in the period will be over the
Pacific Northwest and northern Rockies ahead of the eastern
Pacific trough that eventually moves into the West. Progression
of this trough later in the week into next weekend will spread
precipitation over other parts of the West and then bring a
variety of precipitation types to the central U.S. as low pressure
emerges over the Plains. Ahead of this system, expect most
precipitation east of the Rockies to be confined to a couple
episodes of snow across northern areas with associated surface
waves. The pattern evolution will favor above normal temperatures
over a majority of the western/central U.S. through Wednesday or
Thursday and then a cooler trend over the West and warmer readings
over the East.
...Guidance Evaluation/Predictability Assessment...
Two dominant uncertainties remain within what continues to be an
agreeably depicted mean pattern evolution through the period. The
first involves the east-west shortwave energy forecast to be over
central Canada on Tuesday and then drop into the cyclonic flow
downstream, with Tuesday-Thursday surface low pressure and frontal
system very sensitive to the exact details of the energy aloft.
The upper feature is south/southeast of a closed high and such a
configuration tends to yield low predictability, with
model/ensemble spread demonstrating this idea so far. In latest
cycles the ECMWF/GFS have tended to be most sheared with the
shortwave energy and thus weak with low pressure, while the
UKMET/CMC's more concentrated depiction of energy aloft results in
a stronger surface system. Ensemble means generally reflect the
ideas of their parent models. For now the preference leans on the
weaker side to maintain better continuity until there is reason to
be more confident in the alternative. The second uncertainty
involves the upper trough moving into the West by Thursday. There
has been progress toward better agreement to some degree, as
latest GFS runs have stabilized toward a fairly amplified trough
that had been advertised by most other guidance. The CMC is still
a little questionable as it is more amplified than most other
solutions at some valid times and the new 00Z run has an extra
embedded low within the trough as it comes ashore. The character
of upstream small-scale energy dropping into the overall trough
(00Z CMC an amplified extreme) still complicates the forecast.
The 12Z ECMWF was reasonable for this feature but still strayed on
the fast side with the central U.S. dynamics and surface system by
next Saturday--due in part to being quicker to lift out eastern
troughing.
For the updated forecast, guidance comparisons led to an
operational model emphasis early followed by partial incorporation
of the 18Z GEFS/12Z ECMWF means. ECMWF input consisted of both
the 12Z run and prior 00Z version through the period due to the
older run having some appealing traits for both systems of
interest. Two-thirds total weight of the GFS/ECMWF into early
Thursday yielded the desired outcome for the eastern U.S. wave
whose character remains a significant question mark.
...Weather Highlights/Threats...
Moist flow ahead of the upper trough initially over the eastern
Pacific should continue a Pacific Northwest atmospheric river
event already in progress at the start of the period early
Tuesday. Amounts during Tuesday-Wednesday should be somewhat
lower than in the short range at the start of the week but could
still be meaningful at some locations. Some of this moisture will
extend into the northern Rockies. Progression of the upper trough
into the West after midweek should lead to a lighter trend along
the West Coast and spread precipitation into central California
and some other parts of the West, mostly with light to moderate
amounts of rain and higher elevation snow. Expect precipitation
to expand across the central U.S. late week into the weekend as
western trough energy reaches far enough east to support Plains
low pressure. Best potential for some wintry weather will be over
the northern third of the Plains into the Upper Midwest. Areas
from the Upper Midwest into Northeast may see a couple periods of
snow Tuesday-Thursday in association with clipper systems, the
first one fairly well forecast but the second having much greater
uncertainty for strength/track details. Thus confidence is a lot
lower for coverage and amounts of snow with the second system.
Above normal temperatures will prevail over a majority of the
western and central U.S. Tuesday-Wednesday. Progression of the
initial eastern Pacific upper trough will promote a cooler trend
over the West after midweek and then favor northward expansion of
above normal temperatures (plus 10-15F or so anomalies) from the
South across a greater portion of the eastern U.S. Plus 10-20F
anomalies will be possible for max and/or min temperatures for one
or more days over the Great Basin/Southwest through midweek and
parts of the Rockies/Plains into later in the week. Central
Plains locations could exceed plus 20F anomalies for highs. Areas
from the Upper Midwest to the Northeast will tend to be moderately
below normal and colder air filtering into Montana/North Dakota
could bring highs down to 10-20F below normal by next Saturday.
Rausch
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml