Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
222 AM EST Tue Jan 18 2022
Valid 12Z Fri Jan 21 2022 - 12Z Tue Jan 25 2022
...Heavy Snow/Ice Threat for the Southeast/Mid-Atlantic/Northeast
into Friday/Saturday...
...Overview...
Arctic high pressure will push a cold front through the Deep South
and East later this week, leading to much below normal
temperatures. Moist air fed into the southern and eastern
periphery of the cold airmass is increasingly likely to fuel a
heavy snow/ice threat from the Southeast to the Mid-Atlantic into
Fri. Potential coastal storm development would enhance Mid-Atlanic
to Northeast heavy snow potential Sat. Meanwhile, upper ridging
builds off/along the West Coast as digging Intermoutain
West/Rockies shortwave energy spills snows southward in route to
producing a Southwest closed low by the weekend slated to eject
across the U.S. southern tier early next week.
...Guidance/Predictability Assessment and Weather
Highlights/Threats...
Guidance remains in decent agreement with the large scale mean
flow over the lower 48 highlighted by an upper ridge off/along the
West Coast and upper troughing over the central and eastern U.S..
However, the models have recently been horrendous with run to run
continuity with embedded shortwaves that dig through the mean
upper trough position. In particular, forecast spread remains a
significant timing and amplitude issue with a main shortwave over
the east-central to eastern states Fri/Sat that produces major
placement differences with a potentially impactful coastal low
genesis in the western Atlantic. The 00 UTC ECMWF/UKMET trended
deeper and less progressive with the inland shortwave and
subsequent coastal system. The 00 UTC GEFS also trended in that
direction. The 00 UTC GFS was slightly less progressive and
northward shifted. The 00 UTC Canadian seems in line with its 12
UTC run. It does seem noteable that the 00 UTC model trends now
seem more favorable for significant system develpment. However, it
has been an annoying recent trend for 00 UTC guidance to trend
slower vs 12 UTC guidance, possibly due to diurnal initialization
data sensitivity. Hopefully, model solutions will continue to
converge on a more common solution.
Accordingly and in anticipation, the earlier released WPC product
suite was primarily derived from the most amplified ensemble mean
solution, the ECMWF ensemble mean. Manual adjustments were further
applied to increase shortwave amplitude smoothed out by the mean
and to maintain max WPC product continuity.
There is potential for heavy snow, sleet, and freezing rain
particularly from the southern Appalachians and
Carolinas/Mid-Atlantic into Fri, potentially into the Northeast by
Sat. The pattern will also be favorable for lake effect snow given
cold air in place. Into early next week, guidance agrees to hold
an amplified mean upper trough over the cooled east-central U.S.,
ableit with variations with embedded shortwaves set to dig and
reinforced the feature underneath a deep low centered just east of
the Hudson Bay.
Meanwhile out West, models genrally agree to dig shortwave energy
southward across the Intermountain West Friday leading to a
Southwest U.S/northern Mexico closed low by the weekend. Lead flow
response in advance of expected system ejection out across the
U.S. southern tier early next week would support a modest swath of
overrunning precipitation within a cooled airmass from Texas
eastward across the Gulf Coast. The best chance for snow will
Fri/Sat down through the Rockies as the shortwave impulse moves
through. Other than that, conditions should remain mostly dry,
with slightly warmer than normal conditions for the West Coast
states underneath the ridge, and above normal temperatures are
then expected for the High Plains early next week.
Schichtel
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