Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Mon Jan 24 2022
Valid 12Z Thu Jan 27 2022 - 12Z Mon Jan 31 2022
...Overview...
Latest guidance continues to show a mean upper level pattern that
features troughing over the East, varying degrees of ridging over
the West, and a developing northeastern Pacific trough that may
approach the West Coast early next week. Within this fairly
agreeable regime there are still significant uncertainties
regarding specifics of an eastern U.S. amplified trough that will
likely support a western Atlantic storm Friday into the weekend
with some effects possible over New England in particular, as well
as for a shortwave approaching the West Coast late this week.
Issues near the West Coast may have some influence on the forecast
farther to the east. There are also differences with details of
the late-period northeastern Pacific trough, affecting how much
moisture reaches the Northwest. Between these areas of
contention, a series of weak systems may bring light precipitation
to some areas from the northern tier into the Appalachians. The
forecast temperature pattern remains similar with the East
generally below normal through the weekend and the West into
portions of the Plains above normal for most days.
...Guidance Evaluation/Predictability Assessment...
Even though the large scale mean pattern has been rather
consistent in the guidance, the embedded areas of uncertainty
involve aspects that are smaller in scale and lead to lower
predictability.
Over recent days, most operational models have been varying with
the exact depiction of shortwave energy within the amplified upper
trough that heads into the East and supports Atlantic cyclogenesis
late week into the weekend--thus leading to important differences
in track/timing/strength of the surface system. One positive
trend is a deeper depiction in the ensemble means compared to
previous days, suggesting that member spread may be decreasing
somewhat. However there is still enough track variance among the
guidance to result in a wide variety of potential effects,
especially over New England and to a lesser extent farther south.
On one hand the recent CMC runs and associated ensembles have
tended to be on the northern/northwestern side of the full
guidance spread and the new 00Z run actually brings the track into
New England. On the other extreme the 12Z ECMWF was so far east
that it brought hardly any precipitation at all to New England.
Remaining solutions are between these extremes with the consensus
trend among 12Z/18Z and new 00Z guidance appearing to be somewhat
westward. An intermediate approach provides the best stability
for the time being. A major change in the new 00Z ECMWF
highlights the sensitivity of the forecast, as it now shows a very
deep low just off New England by late Saturday--a little north of
a similarly wound-up UKMET.
Guidance also continues to have difficulty with the details of
shortwave energy approaching the West Coast late this week and
then filtering through the western mean ridge. Latest
GFS/UKMET/CMC runs have been suggesting the potential for an upper
low to close off while recent ECMWF runs and the ensemble means
have kept it as an open wave. The new 12Z ECMWF has trended more
to the other models in principle. These differences first affect
the coverage and amounts of precipitation near the West Coast.
Then the varied handling of this energy leads to various ideas for
how much precipitation may develop over the southern
Plains/western half of the Gulf Coast late in the period. For the
purposes of a single deterministic forecast, prefer to maintain
the open wave depiction for better continuity but with fairly low
confidence.
Elsewhere, there is decent model/mean consensus for the developing
northeastern Pacific trough but its evolution has some complexity
involving multiple features, so details may take a while to
resolve better. This favors a model/mean blend for the time
being. An initial front should be dropping into the northern tier
by Thursday followed by a wave tracking from the northern Plains
through the Midwest and Great Lakes Saturday-Monday. Spread and
run-to-run variability have been fairly typical thus far, with
some gradual detail adjustments in consecutive consensus blends.
The updated forecast started with a blend of 12Z/18Z model runs
early in the period and then started to incorporate 18Z GEFS/12Z
ECMWF means by day 5 Saturday, reaching 50 percent total weight by
days 6-7 Sunday-Monday.
...Weather Highlights/Threats...
Continue to monitor forecasts for the likely Atlantic storm
development late this week and weekend. Recent trends are
increasing the potential that New England could see meaningful
precipitation and wind effects from this system. With lesser
magnitudes of each, there is also uncertainty for what portions of
the Mid-Atlantic may experience. Typical guidance errors for such
systems at this time frame still allow for significant changes to
the current forecast. It is hoped that arrival of some of the
supporting dynamics into western Canada by Tuesday may start to
provide improved refinement to the forecast around then or shortly
thereafter. Before this storm develops, locations across the far
southern tier may see some mostly light precipitation. Some
locations near the West Coast may see an increase in precipitation
with an approaching shortwave/possible compact upper low late week
into the weekend but with low confidence in details. This energy
could eventually support some precipitation over the southern
Plains/western half of the Gulf Coast early next week. Flow ahead
of a northeastern Pacific upper trough should bring rain and
mountain snow into the Northwest but again with low confidence for
timing and amounts. A wavy frontal system should bring mostly
light snow to the Great Lakes and Appalachians late this week.
One or more trailing weak waves may also produce scattered light
snow over areas from the extreme northern tier into the Great
Lakes.
On Thursday northern parts of the East will see lows 10-20F below
normal and locations near the East Coast will see highs 10F or
more below normal. Reinforcing cold air reaching the east-central
U.S. Friday will bring a broad area of temperatures at least
10-15F below normal over the East by Saturday. Most areas should
rebound toward more normal readings by next Monday. Much of the
West should continue to see moderately above normal temperatures
(locally plus 10-15F anomalies) while the northern and central
Plains will likely see one or more days with temperatures 10-20F
above normal (especially Friday-Saturday). Lesser warmth may
extend into the southern Plains by the weekend.
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