Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
250 PM EDT Sun Apr 17 2022
Valid 12Z Wed Apr 20 2022 - 12Z Sun Apr 24 2022
...Wintry Storm threat from the West to the North-Central U.S.
late week/next weekend...
...Weather Pattern Overview...
The departure of the strong low pressure system from New England
will leave a surface high in its wake across the eastern U.S. on
Wednesday. At the same time, an organizing storm system just north
of the Canadian border will bring a cold front eastward across the
north-central U.S. with a weakening low farther south across the
central Plains. Attention then turns to the western U.S. by Friday
with advent of an amplified upper level trough/frontal system with
an enhanced precipitation focus. The cooling/unsettling system
then works inland over the Intermountain West and leads into later
next weekend development of a potentially strong surface low over
the cooled central/northern Plains to include the threat for heavy
wrapping winds/snow/ice on the northern periphery of the system
and an emerging pre-frontal rainfall/strong convection area
broadly underneath and into the warming/moistening east-central
U.S. Meanwhile, a building downstream upper ridge axis over the
Appalachians may allow closed trough development cut underneath
over southern FL and Cuba to increase/focus next weekend rainfall.
...Model Guidance Evaluation...
The 00/06 UTC model guidance suite appears to have above average
agreement on the main synoptic scale features through Thursday
night. By Friday, the GFS remains more progressive with the axis
of the main trough axis across the western U.S., and this
difference is even more apparent going into Saturday/Sunday across
the High Plains. Meanwhile, the 00 UTC CMC and ECMWF are in close
agreement and depict a closed low evolving over the Southwest by
Friday night, and this also has support from the 00 UTC UKMET.
This amplified and less progressive trend continues through next
weekend, leading into deepening trends with cyclogenesis over the
Plains. This would result in an increased and less progressive QPF
swath compared to the 13 UTC NBM 4.0.
Elements of this deepening system can be traced back to former
Pacific Typhoon Malakas that is currently a deep extratropical low
slamming into the Aleutians. Another deep Pacific low expected
track into the Aleutians then the Gulf of Alaska later week/next
weekend also portends a solution on the more amplified side of the
full guidance envelope downstream over the lower 48. Accordingly,
model preference for the later half of the forecast period for the
WPC medium range product suite was a CMC/ECMWF/ECENS mean blend as
a starting point.
12 UTC models overall remain consistent with this plan. The GFS
trended less progressive and the ECMWF/Canadian slightly more
progressive next weekend, a bit more into common alignment. This
seems to bolster forecast confidence in the threat, albeit with
slightly more progression.
...Sensible Weather/Threats...
In the precipitation department, the West Coast region is expected
to remain active with a strong cold front and onshore flow
directed inland across the mountainous terrain of central and
northern California. This spring event will deliver some highly
beneficial precipitation to drought-stricken areas of California,
with the potential for several inches of rain in some areas next
week, and several feet of snow for the Sierra. Elsewhere across
the continental U.S., improving weather can be expected for the
Northeast as the strong storm system moves out of the region. Deep
warming over the East into next weekend may be tempered from the
Northeast down into the Mid-Atlantic by frontal damming that may
prove slower to erode than shown in the models. Another round of
organized showers and storms are expected to develop across the
central U.S. and extending northward to the Great Lakes through
late week as Gulf moisture is advected northward ahead of the
organizing storm system over the central Plains. Additional
moderate to heavy snow is also expected for portions of the
northern Rockies for Friday and into the weekend, with an
increasing threat for heavy snow to spread and intensify in
particular across the northern High Plains and Dakotas/vicinity
next weekend.
Schichtel/Hamrick
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