Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Fri Dec 31 2021
Valid 12Z Mon Jan 03 2022 - 12Z Fri Jan 07 2022
...Multi-day coastal heavy rain and mountain focusing heavy snow
threat for the Pacific Northwest and northern California to the
northern Great Basin/Rockies next week...
...Arctic blast to focus over the north-central U.S.
Tuesday-Friday with snow likely for the chilled Great Lakes states
through the interior Northeast...
...Guidance/Predictability Assessment...
The WPC medium range product suite was mainly derived from a
composite of best clustered guidance from the 00 UTC
ECMWF/UKMET/Canadian days 3/4 (Monday-Tuesday) along with the 13
UTC NBM in a pattern with overall above normal predictability.
Model differences near the surface become increasingly problematic
Wednesday-Friday despite a generally compatible larger scale
pattern evolution aloft. This is not unusual during the cold
season in periods with stark baroclinic zones and phasing
uncertainties. The WPC medium range product suite in this period
was accordingly derived from a composite of better clustered
guidance from the 06 UTC GEFS mean and 00 UTC NAEFS mean that have
a cooler Arctic airmass over time than the 00 UTC ECMWF ensemble
mean. Some added input from the best system compatible 00 UTC
ECMWF and additional manual adjustments added some detail
consistent with the upper flow, pattern recognition and continuity.
...Weather Pattern and Weather/Hazards Highlights..
A cold Canadian surface high will settle far south across much of
the central/eastern U.S. in the wake of the strong cold front to
exit the East Coast by Monday whose coastal low lifts offshore the
Mid-Atlantic. Surface cyclogenesis ensues over the north-central
U.S. Tuesday/Wednesday in response to an amplifying upper trough,
with yet another surge of frigid air in it's wake. Trailing
frontal low genesis offers some moderate trailing frontal focusing
rain potential along with a heavy snow threat spreading mainly
from the Great Lake states to interior New England next
Thursday/Friday with windy/wrapped flow and cold air over the
lakes enhancement.
Protracted periods of heavy coastal rains and heavy mountain
focusing snows will develop from the Northwest and northern
California into the northern Great Basin through early to later
next week as energies from a multi-day Pacific storm system press
inland. Unlike recent events, latest guidance trends suggest this
storm episode is not expected to produce heavy precipitation for
central/southern California. A multi-day heavy snow threat is also
likely for the north-central Rockies/High Plains as further
enhanced by a favorable post-frontal upslope Arctic airmass fetch
with temperatures as cold as 20-40 degrees below normal over the
northern Plains along with dangerous wind chills.
Hamrick/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