Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
151 AM EST Fri Mar 05 2021
Valid 12Z Mon Mar 08 2021 - 12Z Fri Mar 12 2021
...Overview and Guidance/Predictability Assessment...
Models and ensembles agree that an amplified eastern Pacific mean
trough aloft will settle over the West next week. This trough will
support rain and higher elevation snow along with the advent of
below normal temperatures. Meanwhile by Tuesday-Wednesday, a
shortwave expected to eject from the trough will produce a Plains
system to spreads a broad area of precipitation across the
central/east-central U.S.. Ahead of this evolution, eastern U.S.
heights will continue to rise as ridging moves in from the central
U.S. and an upper high builds from Mexico into the Gulf. This will
transition much above normal temperatures from the north-central
U.S. to the East. Forecast spread increases later next week with
upper trough specifics in the West and frontal progressions over
the central and eastern states. This reduces above normal feature
predictability to more average levels.
Accordingly, the WPC medium range product suite was derived from a
composite of quite well clustered guidance from the 18 UTC GFS,
the 12 UTC ECMWF/UKMET and to a lesser degree the 12 UTC Canadian
days 3-5 (Mon-Wed) along with the 01 UTC National Blend of Models.
Shifted focus to the compatible 18 UTC GEFS and 12 UTC ECMWF
ensemble into days 6/7 (next Thu-Fri). Ensemble mean progressions
seem consistent with amplified flow and maintain good WPC
continuity. The latest 00 UTC guidance also seem in line with this
forecast scenario.
...Weather/Threats Highlights...
A good portion of the West has potential for at least some
rain/higher elevation snow during the period under increasing
influence of an unsettling and cooling mean upper trough. Heavier
precipitation should extend from southwestern Oregon through
favored terrain in California, with highest amounts most likely
along the Sierra Nevada. Meaningful though more moderate
precipitation is likely across the Interior West and Rockies.
Energies ejecting into the Plains should produce a multi faceted
system that tracks through northern tier locations Tuesday onward,
with a broad area of precipitation extending across the
northern/eastern Plains and into the east-central U.S. Some wintry
weather may be possible over extreme northern locations. Farther
south, there may be locally moderate to heavy rainfall from the
Great Lakes/Midwest back through the mid-MS Valley and the
Southern Plains currently the most likely areas to see highest
rainfall totals and/or strongest convection. This will be fueled
by Gulf inflow and instability. Activity will mainly focus along a
wavy cold front that may tend to stall later period as upper
troughing settles over the West. This could lead to a pattern with
enhanced training.
Much above normal temperatures will persist over the northern
Plains/Midwest and expand into the Great Lakes through the first
part of next week with readings generally 10-25F above normal.
Daily records should be more numerous for warm lows than daytime
highs. Development and gradual progression of the Plains/Midwest
system and trailing front Tuesday onward will slowly push this
warmth more across the eastern half of the country mid-late next
week. Morning lows should remain as warm as 15-25F above normal
and approach some record values while high temperature anomalies
should be less extreme. Meanwhile, the West will experience a
decent cooling trend spreading across the region from west to east
during the period with highs tending to drop to 5-10F or so below
normal.
Schichtel
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