Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Sat Jan 08 2022
Valid 12Z Tue Jan 11 2022 - 12Z Sat Jan 15 2022
...Overview...
The medium range period will begin on Tuesday with split flow
across the western U.S. as a southern stream closed low drifts
near Baja California through midweek with ridging across the
Northwest in a Rex block pattern. The southern stream low is
currently expected to push into the Four Corners around Thursday
while additional Pacific energy moves toward the West Coast.
Meanwhile, shortwave impulses will track through broad troughing
in the eastern (especially northeastern) U.S. along with low
pressure/frontal systems.
...Guidance/Predictability Assessment...
Reasonably good model agreement and predictability exist early in
the medium range period with deep upper troughing across the East
and ridging across the West undercut by the southern stream upper
low. Most guidance for the 12/18Z (yesterday) cycle was aligned
and consistent with previous runs with the position and closing
off the initial southern stream low feature at least for a period
on Tuesday/Wednesday. The main exception in terms of position was
the 12Z CMC, which has a center position farther to the southwest
compared to the vast majority of other guidance. Then energy
tracking eastward across the Pacific and approaching the West
Coast Thursday shows considerably more variability with strength,
position, and track as well as whether or not the energy closes
off (which GFS runs had been persistent with until the 18Z run).
Trends in recent guidance indicate that impulse may drift in the
eastern Pacific through late week or at least stay limited to the
Northwest with less interaction with the initial low, but with low
confidence. CMC runs are the exception to this in terms of
deterministic guidance, and spaghetti plots show tremendous
variability in the details of the western U.S. flow by Friday and
Saturday.
Meanwhile in the East, initial model agreement is quite good with
the trough axis over the Eastern Seaboard early Tuesday, which
lifts away and relaxes the amplitude of the overall flow by
midweek, though additional shortwaves approach. One upstream
shortwave develops some considerable differences among models by
Wednesday and Thursday. In terms of the 12Z model cycle, the UKMET
and CMC appeared to be outliers in how deep the energy from the
shortwave causes the trough axis to dig in the east-central U.S.,
as confirmed by the 12Z CMC the deepest and the UKMET compared to
individual ensemble members' 500mb heights. However, incoming 00Z
guidance including the GFS and ECMWF show deeper troughing than
their previous runs, even closing off a low across the Atlantic by
Friday, so the trend appears to be in a deeper direction.
The WPC fronts/pressures forecast was based mainly on a blend of
the 12Z/18Z GFS and 12Z ECMWF early on, phasing in the GEFS and EC
ensemble means as the period progressed to downplay the specifics
of a particular model runs. At the time, did not favor the
CMC/UKMET for the reasons above, but given the way 00Z models are
trending, perhaps their influence with a deeper trough in the East
would have been helpful.
...Weather Highlights...
Drier conditions are likely over much of the contiguous U.S. on
Tuesday as large surface highs influence the Intermountain West to
the central U.S. behind a cold front, and high pressure will push
into the East on Wednesday. Showers could linger over Florida on
Tuesday after the front passes through, while generally westerly
flow could cause lake effect snow downwind of the Great Lakes at
times through the week, though in lesser amounts than during the
short range period Monday. 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 could 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.
Cold air will be in place over the Upper Midwest and spreading
into the Northeast on Tuesday, 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. By the end of the week temperatures are
currently forecast to moderate close to normal.
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