Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
136 PM EST Mon Feb 01 2021
Valid 12Z Thu Feb 04 2021 - 12Z Mon Feb 08 2021
...Midweek Southwest U.S. system to progress to the
Plains/Midwest/Northeast later week followed by major arctic
outbreak over the central and eastern U.S. by the weekend...
...Guidance/Predictability Assessment...
Aside from the 00Z UKMET, the rest of the deterministic guidance
showed very good agreement and clustering at the start of the
period such that the WPC blend was comprised mainly of the 00Z
ECMWF/06Z GFS/00Z CMC for days 3-5. The 00Z UKMET was too
deep/progressive with the upper level as it works across the Great
Lakes. Other areas of uncertainty were across the Southwest where
a potential closed low pinches off as the longwave trough develops
over the CONUS. The ECMWF features this solution the most while
the GFS and CMC to some degree are a bit more progressive. The WPC
blend resulted in a compromise solution with some favoring toward
the ECMWF idea. In the big picture sense, all the deterministic
models and ensembles show a significant longwave trough over the
central CONUS by the end of the period which should allow for a
significant intrusion of Arctic air to overspread the northern
tier and portions of the east.
...Weather/Threats Highlights...
Upper troughing driving through the Southwest/Rockies will produce
a swath of terrain enhanced snows into Thursday. System ejection
into the Plains still offers additional northern stream trough
phasing uncertainties and a complex frontal structure, but suspect
that a deepening low will organize and lift to the Great Lakes
into Friday. Enhanced snows are expected near and to the north of
the main cyclone track from the windy Midwest/Great Lakes to the
Northeast. Upstream, expect a swath of heavy terrain snows are
forecast from the Northwest to the north-central Rockies late week
with a series of potent shortwaves that subsequently dig into an
emerging/amplified central U.S. upper trough position this
weekend. This will act to drive a frigid arctic airmass fully
southward through the central then eastern U.S.. Interaction with
a lingering wavy front trailing from the aforementioned lead
system over the East may favor Piedmont/coastal rains and inland
snows from the OH Valley/Appalachians to the Northeast, though
there is much uncertainty on any coastal storm from the
Mid-Atlantic to Northeast late in the weekend to early next week.
Temperature departures will reach 15-30F over the northern tier
and Great Lakes by day 5/6 and overspread the East Coast by day 7.
For portions of the northern Plains and Upper Midwest, readings
may not break 0. The much below normal temperatures will even
spread southward into portions of the Deep South and north Florida
where daytime high departures of 5-15F are possible.
Taylor
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