Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sun Apr 10 2022
Valid 12Z Wed Apr 13 2022 - 12Z Sun Apr 17 2022
...Potent storm system to bring heavy snow/blizzard conditions
across the Northern Plains with heavy rainfall and severe weather
from the Gulf Coast to the Mid-Mississippi Valley...
...Overview...
The latest guidance continues to support an active weather pattern
across the lower 48 into next weekend. The main system of interest
is an amplified trough/developing closed low over the northern
U.S./Upper Midwest which should spin up a rather impressive
looking spring storm system. This system brings a full array of
weather hazards mid to later next week... including heavy snow and
possible blizzard conditions to the north and west of the low
track across the Northern Plains and severe weather and heavy to
excessive rainfall in the warm sector. Upstream, uncertainty is
high regarding flow into the Western U.S. but changes are that
another trough may kick out into the West next weekend.
...Guidance Evaluation/Predictability Assessment...
Models continue to show higher than avearge uncertainty
surrounding an amplified trough in the central U.S. which
eventually develops into a deep closed upper low tracking across
the Northern Plains and Upper Midwest. While all models now
suggest a rather significant storm system, there remains a lot of
questions on track and timing of the surface low and attendent
cold front across the South and Midwest. The 18z/Apr 9 GFS is the
fastest with closed low development, but is actually not too far
out of line with location of surface low pressure at day 3-4 in
the Upper Midwest. After this, likely a result of a much blockier
Western Atlantic ridge, the GFS gets much faster with steering
this low quickly northward, while the ECMWF and CMC suggest the
upper system is sheared/redevelops over the Great Lakes/eastern
Canada next weekend. Ensemble means do not really give a clear
answer here as they generally continue to follow their
deterministic counterparts. In the interest of continuity,
continued to favor the ECMWF over the GFS, with increasing
weighting towards the ECENS/GEFS means late period.
Beyond Wednesday/Thursday, flow upstream across the West becomes
very uncertain with some significant model variability especially
by the day 6-7 time frame. There is increased consensus on some
kind of open shortwave (or closed low) into the Pacific Northwest
on Friday. Models suggest another trough into the West next
weekend, but the details on embedded energy within that trough and
amplifcation become very murky next weekend with very poor model
run to run continuity. A blend heavily weighted towards the
ensemble means gets some weak troughing across the West with a
hint at low pressure once again moving into the Plains next Sunday.
...Weather Highlights/Threats...
Some lingering snowfall is likely as the period begins Wednesday
across the West, but by then a well developed storm should be
tracking across the northern Plains/Upper Midwest with a
significant snow storm likely to the north and west of the surface
low across the Dakotas and northwest Minnesota. Heavy snowfall,
possibly exceeding a foot in some locations, with gusty winds
could create blizzard conditions leading to hazardous travel and
power outages in many areas. Meanwhile in the warm sector, there
will be increasing coverage and intensity of rain and
thunderstorms ahead of the attendant cold front given persistent
Gulf moisture and instability. The Storm Prediction Center's
extended outlook indicates severe potential across the lower and
middle Mississippi Valley on Wednesday, with more uncertain
potential farther east into the Southeast on Thursday. Heavy to
excessive rainfall concerns may focus on the southern side across
the Lower Mississippi and Tennessee Valley, but farther north,
dynamics wrapping around the low may support an additional area of
modest rainfall across the Upper Mississippi Valley. This may
cause localized flooding and flash flooding issues there as well
particularly if rain falls over frozen or snow covered ground.
Rainfall may linger through Friday across the Southeast as the
western part of the boundary stalls across the region.
Out West, moderate to heavy rain/mountain snows are possible
across parts of California/Oregon with the next low pressure
system moving in late this week. Moisture looks to spread east
into the intermountain West, with more uncertainty by next Sunday
regarding precipitation into the Plains.
Much below normal temperatures (with anomalies 20+ degrees below
average) will shift eastward with time into the northern Plains
into next weekend. Some moderation is likely by later in the week
across the West, though still below normal with additional
troughing moving in. Meanwhile, ahead of the big storm, expect
temperatures from the south-central U.S. to the East to be above
normal, but trending back towards normal following passage of the
cold front.
Santorelli
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, experimental excessive rainfall
outlook, 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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml