Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
150 PM EST Fri Jan 07 2022
Valid 12Z Mon Jan 10 2022 - 12Z Fri Jan 14 2022
...Overview...
The medium range period will begin on Monday with an amplified
upper flow pattern as a trough extends southward from a deep upper
low over east-central Canada and ridging prevails across the
western U.S. and Canada. A split flow pattern is likely to develop
across the eastern Pacific and West, as a southern stream low
drops southward near the California coast through the early part
of the workweek. Another Pacific shortwave should approach the
West Coast around midweek with guidance showing varying ideas for
what form it will take thereafter and how it may interact with the
leading upper low. Meanwhile in the East, the pattern may
deamplify somewhat by mid-late week but one or more shortwaves of
uncertain strength and timing will likely track through the
lingering broad mean trough.
...Guidance/Predictability Assessment...
Reasonably good predictability exists early in the period as model
guidance has remained consistent and agreeable with the deep upper
trough across the East and ridging across the West. However the
full array of guidance has not improved confidence with ongoing
uncertainties in the rest of the forecast, but there are some
common themes that provide decent continuity in principle.
There is still a majority cluster that has a compact closed low
tracking along the central-southern California coast into far
northern Baja California Monday-Wednesday with subsequent ejection
in response to upstream flow. The new 12Z CMC has deviated from
consensus by pulling its closed low from a more southern part of
the overall shortwave. Then models/ensembles continue to show
their divergence for details of the next Pacific shortwave.
Multiple GFS runs have been closing a low over the eastern
Pacific, and now the 12Z CMC does the same farther south, while
the 00Z ECMWF/CMC agreed more with the ensemble means which have
been maintaining an open shortwave at least until the feature
crosses the West Coast. Interestingly by late next week the
06Z/12Z GFS runs are not far from the majority solution for the
large scale pattern after subtracting their eastern Pacific upper
low. The 12Z ECMWF provides yet another option, trending somewhat
slower/more separated and bringing the best concentration of
energy into the Northwest instead of digging into the Great
Basin/Four Corners. Preference based on 00Z/06Z guidance was to
follow the model consensus for the leading Pacific feature and
then weight the forecast more to the 00Z ECMWF/CMC and 06Z
GEFS/00Z ECMWF means when the next shortwave comes into the
picture.
Meanwhile in the broad cyclonic flow farther east, the best signal
exists for a shortwave to cross the eastern half of the country
around Wednesday-Thursday. As can be the model's occasional bias
with upper troughs, the latest CMC runs are quite amplified (even
pulling off a closed low east of Florida by Friday in the new 12Z
run). Even if not quite an outlier, these CMC runs are extreme
compared to most of the full ensemble envelope.
The late-period transition to half means/half models (versus all
models early) kept somewhat more 00Z ECMWF input relative to the
06Z GFS/00Z CMC given the desire to downplay GFS specifics near
the West Coast and the CMC in the East.
...Weather Highlights...
Drier conditions are likely over much of the contiguous U.S. for
the early part of next workweek as large surface highs influence
the Intermountain West to the central U.S. behind a cold front.
Showers could linger over Florida on Monday as the front passes
through, while generally westerly flow causes lake effect snow
downwind of the Great Lakes especially on Monday but with the
possibility for additional rounds as the week progresses. The
Pacific Northwest should see periods of precipitation as fronts
approach the area, with higher totals over typical upslope areas
of the Olympics and Cascades. Locally moderate to heavy activity
may be possible over the Olympics and vicinity around midweek when
the area may be on the southeast fringe of an atmospheric river
event aimed at Vancouver Island. The upper low initially dropping
southward near the California coast may spread moisture into the
Southwest by Tuesday-Wednesday. This precipitation should be
fairly light but heavier rainfall may develop over the Southern
Plains and Lower Mississippi Valley by mid-late week as the upper
low tracks/shears northeastward and the surface pattern becomes
more favorable for drawing moisture northward from the Gulf of
Mexico. It will take additional time to refine the details of
rainfall coverage and magnitude though.
The next round of arctic air will be in place across the Northern
Plains and Upper Midwest on Monday, with temperatures of 10-25F
below normal and maximum temperatures staying below 0F in some
areas. By Tuesday this chilly air will spread into the
Northeast/Mid-Atlantic in modified form, with high temperatures
10-30F below average for one of the coldest days of the season
thus far. Then the central U.S. will see a pronounced warming
trend next week with expanding coverage of max/min temperatures
10-20F above normal Tuesday onward. Some locations in the
northern two-thirds of the Plains may see even warmer readings
mid-late week. Across the West expect to see daytime highs within
10F on either side of normal through the period, while above
normal lows should become more prevalent with time. Best
potential for one or more days with plus 10F or greater anomalies
for lows would be over the Southwest and Pacific Northwest as
separate features bring clouds/moisture into those regions.
Rausch/Tate
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