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Extended Forecast Discussion
 
(Latest Discussion - Issued 1901Z Jan 26, 2022)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Jan 26 2022

Valid 12Z Sat Jan 29 2022 - 12Z Wed Feb 02 2022

...Coastal winter storm threat from the Mid-Atlantic to especially
New England Friday into the weekend...


...Overview...

Early in the medium range period from Saturday into early Sunday,
a deep upper trough reaching the East Coast will likely close off
an embedded upper low that tracks near the New England coast. The
evolution aloft will support further deepening of strong low
pressure just off the East Coast and direct the system northward,
from east of the Mid-Atlantic coast into the Canadian Maritimes.
This strong coastal storm may cause heavy snow in the coastal
Mid-Atlantic region with higher confidence for heavy snow over the
Northeast, where high winds and coastal impacts are also likely
through the weekend. At the same time a weak eastern Pacific
trough/upper low will cut through the southern part of initial
ridging over the West. From late weekend into next week a more
potent upper trough will push into the West and steadily amplify,
ultimately flipping the upper pattern as a ridge axis reaches the
East Coast by Wednesday. This configuration should lead to a
pronounced increase of precipitation over the central U.S. by the
end of the forecast period.

...Guidance Evaluation/Predictability Assessment...

Model guidance for the most recent couple of cycles continues to
show a rapidly deepening (bomb) cyclone in the western Atlantic
over the weekend, but continues to waffle somewhat with its exact
track, and the relatively fine-scale wobbles can cause notably
different weather impacts. Latest guidance continues to favor an
intermediate/consensus approach for depicting the western Atlantic
storm during the weekend. A significant key to the forecast of the
surface low by late Saturday appears to be exactly when, where,
and how deeply the upper low within the overall trough closes off.
ECMWF runs have been reasonably persistent on the earlier/deeper
side with GFS runs at little later/weaker. Overall the forecast
position for the low on Saturday and Sunday was very similar to
the previous WPC forecast issuance, per the 00Z/06Z model
consensus and taking somewhat of an average position between the
slightly slower EC other faster models. However, incoming 12Z
guidance has shown a slightly eastward/more offshore trend
particularly on Saturday.

Models continue to improve their agreement with the small upper
trough/low moving from the Pacific into the Southwest over the
weekend and the Southern Plains early Monday before weakening as
it heads into a developing mean ridge in the East. However, more
model differences arise with the deeper upstream troughing
expected to dig during the first half of next week in the West.
The general trend in the 00Z/06Z model guidance was a slightly
faster trough axis moving eastward especially by
Tuesday-Wednesday, which pushed the cold front ahead of it faster
than the previous forecast. There is still considerable
uncertainty with the multiple pieces of energy serving to
create/dig this trough, which mainly stem from high
latitude/Pacific regions with low predictability. Of the 00Z model
cycle, the CMC showed some stream separation producing a southern
stream low diving off the coast of California Monday-Tuesday
unlike other guidance. This appeared to be somewhat of an outlier
based on consensus and most individual ensemble members, but the
new 12Z GFS ended up looking quite similar to that 00Z CMC, while
the 12Z CMC ended up without this pattern, closing off a southern
stream low well west in the Pacific as did the incoming 12Z ECMWF.
This is just an indication that though model guidance may indicate
agreement at times, there is still low confidence in the details,
and the forecast still may go through changes with the trough axis
and frontal timing.

A multi-model deterministic blend was used early in the medium
range forecast period, with the 00Z/06Z GFS runs and the 00Z
ECMWF, CMC, and UKMET. Gradually increased the incorporation of
the GEFS and EC ensemble means to about half by the end of the
period given increasing model differences and uncertainty.

...Weather Highlights/Threats...

To start the period Saturday, heavy snow is likely across the
Northeast with possibly some snow lingering in the coastal
Mid-Atlantic region. Latest forecasts show the highest confidence
in heavy snow amounts likely near coastal New England. Significant
coastal impacts are possible in the Northeast, including coastal
flooding and beach erosion. Additionally, strong winds may cause
blowing snow and some damage. Hazardous travel conditions are
likely in parts of the region. See the WPC website for updated Key
Messages on the system and check your local forecast at
weather.gov.

It still appears that the upper trough/low that may track into
California and the Southwest this weekend may be weak enough not
to produce much if any precipitation over that region. Its
strength and track thereafter will determine how much
precipitation may develop from the Gulf Coast northward by the
first part of next week. Over the past day guidance has started to
show some convergence toward the idea of at least some meaningful
rainfall along and north of the western half of the Gulf Coast by
Monday. Moisture ahead of a northeastern Pacific upper trough
should begin to move into the Northwest on Sunday and then
continue to spread across more of the West with time as the upper
trough moves inland and amplifies. Highest totals of rain/mountain
snow should be over the Pacific Northwest, but amounts do not
appear too significant at this time. Toward midweek the western
trough and leading surface front will interact with a healthy flow
of Gulf moisture to produce a rapidly expanding area of
precipitation, some of it potentially becoming moderate to heavy
in the south-central U.S. Lighter wintry precipitation will be
possible over northern latitudes. A series of waves/fronts may
bring episodes of light and scattered snow into parts of the Great
Lakes before the larger scale pattern changes.

The eastern U.S. will be quite chilly through the weekend with
broad coverage of temperatures 10-20F below normal, including
subfreezing lows extending into portions of Florida. Areas from
the Mississippi Valley to Appalachians should see a moderating
trend from west to east. Aside from some below average readings
over Texas and vicinity, much of the Plains will see above average
temperatures from the weekend into next week with readings up to
10-20F or so above normal, locally higher. This warmth will
progress into the eastern half of the country early-mid week with
the increase of Gulf moisture helping to raise min temperature
anomalies in particular by Wednesday. Moderately above average
temperatures over the West during the weekend will trend lower
next week with the arrival of an amplifying upper trough, and
5-15F below normal highs may extend from the Interior West into
the High Plains/northern tier by Tuesday-Wednesday.

Tate/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