Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
217 PM EST Thu Jan 13 2022
Valid 12Z Sun Jan 16 2022 - 12Z Thu Jan 20 2022
...Heavy snow likely from the Applachians to the interior
Mid-Atlantic and Northeast with significant icing possible for
parts of the Carolinas...
...Overview...
The most notable weather feature during the medium range period is
a developing surface low pressure system that slides across the
Southeast on Sunday and then pivots northward near/along the East
Coast ahead of a potent mid-upper shortwave trough. This will
cause impactful wintry weather to spread across much of the East
early next week. However, some lingering uncertainty remains with
the exact low track, lending to low confidence in precipitation
type (which could change in some locations as the event
progresses), the axis of the heaviest snow, and the westward
extent of the snow. Meanwhile in the West, mainly dry conditions
are expected underneath surface high pressure, with the exception
of light precipitation in the Pacific Northwest and Northern
Rockies as weak fronts track through.
...Guidance/Predictability Assessment...
The model guidance for the 00z/06z cycle show reasonable agreement
regarding the Southeast/East Coast surface low Sunday-Tuesday. The
new 12z guidance sticks pretty close to previous runs, with just
the typical run-to-run wobble variance. All of the deterministic
solutions now keep the low inland, with the 06z/12z GFS a hair
east, and the UKMET continuing to stick farther south. The
ensemble means are also a bit east of the deterministic solutions,
though still mostly along or just inland of the coast.
Interestingly enough, the 06z/12z GEFS mean continues to keep it's
low center offshore and displaced well to the east of its
deterministic counterpart, though there are a fair number of
ensemble members with an onshore low. WPC prefers a track a little
closer to the deterministic solutions, given the trend over the
past couple of days has been westward. The closest proxy to the
forecast was a blend of the 00z ECMWF and CMC, which places the
low over the Philadelphia region on Monday morning, and very close
to that of the previous WPC forecast as well. Given the spread in
the individual ensemble members, there still a fair amount of
uncertainty in the exact low track and even subtle shifts east or
west could create large changes in the impacts for especially the
major metropolitan cities along the I-95 corridor.
Elsewhere, ridging is likely to have hold of the West early this
week, other than a meandering southern stream upper low centered
offshore of California. which should track eastward and eventually
join with the main flow by around Tuesday. Then there is good
model agreement for an amplified ridge over the West Coast by
Thursday drifting eastward from the Pacific, with some model
differences in possible embedded shortwaves particularly shown by
the GFS runs. Meanwhile, additional shortwaves reinforce troughing
centered over the Great Lakes Wednesday-Thursday, for which there
is reasonable model agreement on the next well defined cyclone to
traverse the Upper Midwest/Great Lakes and into eastern
Canada/northern New England by next Thursday.
The WPC medium range forecast was based on an initial blend of the
00Z/06Z deterministic guidance favoring the ECMWF and CMC for days
3-4. After this, added introduced increasing amounts of the
ensemble means to help mitigate some of the later period smaller
scale details differences. Overall, this presented a forecast very
close to previous WPC continuity.
...Weather Highlights/Hazards...
The surface low lifting from the Southeast and up the East Coast
will bring with it a full array of weather hazards and threats. At
this point, heavy snows are most likely in the Tennessee
Valley/southern Appalachians beginning this weekend, spreading
northward along/on the backside of the deepening low and generally
west of the I-95 corridor in the Mid-Atlantic and the Northeast
Sunday night into Monday. For locations east/along I-95 (including
the major metro areas of DC, Philadelphia, and New York City),
precipitation may start out as a quick burst of accumulating snow,
with a changeover to sleet and/or plain rain as warmer air filters
in from the east. Chances are also increasing for a potentially
significant icing event, especially from parts of northeast
Georgia, through parts of the Carolinas, and into central Virginia
where warm and moist Gulf of Mexico inflow will overrun initially
cold air at the surface. WPC has both the snow and ice threats
highlighted in todays hazard outlook. To the south, moderately to
locally heavy rain likely moves up the immediate East Coast Sunday
into Monday. Gusty winds surrounding the surface low may create
high waves off the coast leading to possible coastal flood
concerns along the Northeast coastline. Of course, all of this is
highly dependent on the exact track of the surface low and even
small adjustments back to the east could bring heavy snow
potential into even coastal parts of the East.
Elsewhere, after the main low exits northeast of the U.S. on
Tuesday, another low pressure system is forecast to track over the
north-central U.S. in response to a mid-upper shortwave and bring
some snow to the Upper Midwest and Great Lakes, with possibly
higher totals near typical lake enhancement areas. The West could
see some light precipitation during the period, particularly over
the Pacific Northwest and into the Northern Rockies early next
week, with mainly dry conditions elsewhere. Rain could develop
again across the Lower Mississippi Valley and Southeast beginning
Tuesday and increasing Wednesday with return flow from the Gulf of
Mexico.
Cooler than normal temperatures are expected generally over the
eastern U.S. early next week, with particularly chilly lows below
0F in the interior Northeast Sunday morning, about 15-25 degrees
below average. The West to the Plains can expect generally above
average conditions through Tuesday. Then as a cold surface high
drops into the north-central U.S. Wednesday and Thursday,
temperatures will fall to 10-20F below normal in the Upper Midwest.
Santorelli/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