Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
215 AM EST Tue Jan 11 2022
Valid 12Z Fri Jan 14 2022 - 12Z Tue Jan 18 2022
...Overview...
Mean ridging is likely over the West during the medium range
period, though with the possibility of shortwaves tracking through
the mean flow while southern stream troughing lingers near or
offshore the California/Baja California coast. Meanwhile in the
north-central to eastern U.S., rounds of upper troughing are
expected, with surface lows developing in response. These features
could cause meaningful snow over parts of the Midwest on Friday
before model solutions diverge with the shortwave/low tracks,
which keeps confidence low for any impactful wintry weather
farther east in the Appalachians and Eastern Seaboard.
...Guidance/Predictability Assessment...
Model guidance for the 12/18Z cycle shows okay agreement for the
large-scale pattern but with differences in some impactful
details. At the beginning of the period Friday, a surface low in
the Atlantic demonstrates reasonably good agreement that it will
be well off the Eastern Seaboard given a trough axis basically
over the East Coast. That surface low should deepen considerably
and may affect the Canadian Maritimes by Saturday. Farther
upstream, models agree that shortwave energy will be spilling into
the Midwest on Friday and continuing to dig Saturday. However, the
shortwaves and associated surface low(s) show more variability in
their tracks. Overall the trend continues to be southward in the
deterministic models especially, as shown by the 12/18Z GFS and
ECMWF, while the 12Z CMC was well north (00Z CMC has come south).
Guidance for the most part takes the surface low across the
Southeast before turning northeastward over the Atlantic. Ensemble
mean guidance is a bit farther north with the low center, and felt
like following closer to their track for the surface low was a
safer bet given the ensemble member spread. After that on
Sunday-Tuesday, there is decent clustering in the guidance for a
southern Canada/Great Lakes system with associated fronts, as
another shortwave originating from the northern Pacific drops into
the north-central and then east-central U.S. This shortwave should
remain more consolidated as it rounds the Pacific ridge, which
hopefully will provide better predictability (at least for the
front if not low pressure) than has been the case for other
shortwaves.
For the West, even on day 3/Friday there is uncertainty about
shortwave energy breaking up the mean ridge. The 12Z EC/CMC
centered a mid-upper low over the northern CA/NV border, right
over the ridge axis in the GFS runs. It looks like the newer suite
of 00Z guidance demonstrates better agreement. Southern stream
energy also shows differences in positioning among model guidance
as it meanders, from well offshore in the Pacific to the western
U.S. The 12Z CMC appeared to be a particular outlier as it takes
the energy eastward even into the Southern Plains by Tuesday,
against consensus and basically all ensemble members.
For the medium range forecast, favored an initial blend of the 12Z
ECMWF, UKMET, CMC and 18Z GFS favoring the ECMWF somewhat. Then as
the period progressed, increased weighting of the GEFS and EC
ensemble means to about half the blend by days 6/7, while taking
out the 12Z CMC from the blend. This provided the most coherent
overall evolution, and while significant further changes may
occur, continuity from the previous forecast on days 3-6 was
fairly good.
...Weather Highlights...
While deepening Atlantic low pressure late this week should stay
far enough offshore to keep a majority of precipitation east of
New England on Friday, strong winds will be possible due to the
tight gradient between this storm and eastern Canada high
pressure. The shortwave and surface low dropping southeastward
from the northern tier late this week will likely bring a swath of
wintry precipitation across portions of the Midwest, followed by
some of this precipitation extending across the eastern U.S. this
weekend. Guidance signals are improving for a band of significant
snow that may cover parts of Minnesota/Wisconsin/Iowa/Illinois
around Friday-Friday night, albeit with some uncertainty remaining
for location and magnitude as well as exact timing. Confidence
remains fairly low for coverage and amounts of any wintry
precipitation farther east. Latest trends continue to suggest a
farther south axis over the East with lower probabilities over the
Northeast initially, though if the low turns significantly
northward, snow could spread into the Northeast Sunday on the
backside of the low track. The south-central and southeastern U.S.
should see mostly light to moderate rain along the southern side
of the precipitation shield. An area of light snow may extend
across the Upper Midwest into the Great Lakes around Sunday-Monday
with the system moving into the region. The most likely forecast
scenario has generally light and scattered precipitation over the
West during the period. There is a lower probability of more
organized activity over a larger area if upper flow details end up
gravitating to the less likely side of the guidance spread.
Temperature-wise, the central U.S. will see mild conditions on
Friday, with lows 10-20F above average while 10-15F above normal
highs are expected for the Southern Plains. Warmer than average
temperatures should continue into early next week for portions of
the Plains. Meanwhile, colder than average temperatures are likely
for the Great Lakes to the Northeast through the weekend, with
Saturday the coldest day in the Northeast with temperatures 15-25F
below normal. The West should see temperatures within about 10
degrees of normal, with a tendency toward slightly warmer than
average conditions especially for lows.
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