Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Wed Feb 16 2022
Valid 12Z Sat Feb 19 2022 - 12Z Wed Feb 23 2022
...Overview...
The medium range period will begin Saturday with generally quiet
weather, besides a clipper system bringing snow to the Great Lakes
region. Then as next week begins, troughing is forecast to develop
in the West and slowly track eastward along with a strong frontal
system. Precipitation chances should increase in the West with
this pattern and spread into the central U.S. once again by next
Monday through Wednesday, with the possibility of northern tier
snow and southern U.S. rain.
...Guidance Evaluation/Predictability Assessment...
Recent model guidance shows good agreement overall with the large
scale pattern even through the middle of next week, with some
typical differences in the smaller scale details. To start the
period, the surface low/clipper over the Great Lakes and
upper-level energy supporting it have good consensus among 12/18Z
models. A less certain feature during this timeframe is a compact
shortwave tracking into the West ahead of the main larger scale
trough. Overall recent models have trended stronger with this
initial energy, with increasing consensus for a closed low likely
centered just west of California on Saturday. The GFS was the
slowest model to come to this conclusion (the 12Z had its low
displaced east and the 18Z run showed an open trough), but the 00Z
GFS does show a closed low in line with other guidance. Though
there is better agreement now, considering the small scale of the
low rounding the Pacific ridge, additional shifts in the forecast
are possible.
Then there is good agreement for energy to spill into the West and
develop troughing as next week begins, while much of the central
and eastern U.S. shifts to zonal flow and then ridging. 12/18Z GFS
runs remain among the strongest, specifically with closing off a
low within the trough even by early Sunday sinking into the
Pacific Northwest, while the 12Z CMC was slightly east with its
trough axis by around Tuesday compared to consensus. The phasing
differences with potential stream separation are causing minor
model differences that could continue to be an issue with the
evolution of the troughing. The ECMWF has been more consistent and
favored among the deterministic guidance, though both the 12Z and
new 00Z runs may be a bit slow with lingering energy across the
West by Wednesday. Despite these model differences, the theme of
troughing developing in the West for the first half of the week
slowly shifting eastward as well as sending northern stream energy
across the north-central U.S. by midweek is consistent.
The WPC forecast utilized a multi-model deterministic blend of the
12/18Z guidance for the early part of the period, slightly
favoring the ECMWF and CMC. Phased in some GEFS and ECMWF ensemble
mean guidance for the latter part of the period, ending up with
about half deterministic models and half means by day 7,
mitigating the individual model eccentricities. The main
difference from the previous WPC forecast was a continued trend
northward with the axis of heaviest QPF across the Mid-South
Monday-Wednesday of next week.
...Weather Highlights/Threats...
Lingering snow is forecast on Saturday across the Great Lakes
region with the clipper system, with generally light to perhaps
locally moderate amounts. Mainly dry conditions are expected
elsewhere on Saturday other than a few showers possible in
Florida, except that precipitation will be increasing in the
Pacific Northwest and Northern Rockies with the upper trough
coming in. Coastal and valley rain and mountain snow are likely
over the Pacific Northwest spreading into California, the Great
Basin, and the Rockies through the early part of next week. Snow
could also spread farther east into the northern High Plains
Sunday and into the rest of the northern tier states as the first
half of the week progresses. The confidence in the axis of
heaviest snow and snowfall amounts remains somewhat low. Farther
south, moist inflow is forecast to return to the south-central and
southeastern U.S., increasing chances for rainfall that could
become heavy over the Mid-South in particular by Monday and
Tuesday.
Temperatures over the weekend are expected to be above normal for
parts of the West into the Plains, with the largest anomalies of
highs 20+ degrees above average over South Dakota and Nebraska.
Meanwhile, cooler to near average temperatures over the eastern
third of the country Saturday will warm Sunday. As the pattern
amplifies, the south-central U.S. to the East Coast will further
warm through the first half of next week, with widespread highs
10-20F and lows 20-30F above normal. Meanwhile, a cold Arctic high
is forecast to shift into the north-central U.S., leading to well
below average temperatures initially across the northern High
Plains and spreading southward through midweek. Temperatures in
some places could be 30 or more degrees below normal, and highs in
the single digits are expected for Montana and the Dakotas Monday
and Tuesday.
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