Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Thu Apr 07 2022
Valid 12Z Sun Apr 10 2022 - 12Z Thu Apr 14 2022
...Active weather is likely next week, with heavy snow spreading
from higher elevations of the West into the north-central U.S. and
heavy rain and severe thunderstorm chances in the south-central
CONUS...
...Overview...
Latest guidance continues to show an amplified pattern in which
one upper trough departs from the East after Sunday while energy
digging in from the northeastern Pacific reinforces western U.S.
mean troughing that should finally emerge into the Plains by
around midweek. There is a decent signal in the guidance that this
pattern should produce active weather over a significant portion
of the lower 48 next week--including rain/snow over the West,
eventually a vigorous low pressure system over the Plains/Upper
Midwest with some snow to the northwest of its track, and a threat
for areas of heavy rainfall plus strong to severe convection over
some southern areas of the central U.S. However within this broad
theme there are a number of uncertainties for details that temper
confidence in specifics of the forecast, not only for the main
area of focus over the western-central U.S. but also frontal
position over the East due to differences in how leading shortwave
energy initially ejecting across the Plains ultimately evolves.
...Guidance Evaluation/Predictability Assessment...
Model guidance remains consistent with the upper trough departing
from the East early in the period. And fortunately, the 00/06Z
model cycle (AND NEW 12Z???) is showing better agreement compared
to the last few cycles with the western trough as well, though
with typical lingering differences in the details. One such detail
is leading shortwave energy in the base of the trough over the
northern Rockies/High Plains early Sunday that shows differences
in its ejection across the northern tier and its effects on
frontal position in the north-central and northeastern U.S. by
Monday-Tuesday. The 00Z UKMET and GFS were among the stronger
solutions with this shortwave and pushed the front farther south
compared to the 06Z GFS/00Z ECMWF and CMC that deflected the
shortwave on the northern side of the ridge. The WPC forecast
leaned toward the latter cluster given continuity and not much
support for the southward extent of the UKMET especially for Great
Lakes shortwave in individual ensemble members.
The next shortwave with notable differences stems from energy in
the Gulf of Alaska in the short term, and is forecast to drop
south across the northeastern Pacific/western Canada coast to form
possibly a potent shortwave near the Pacific Northwest on Monday.
This feature varies somewhat with its position but particularly
varies in strength, which affects a surface low underneath as
well. Most guidance is now indicating a small closed upper low but
the 00Z and new 12Z ECMWF are persistent in showing an open
shortwave farther east in the northwest and a weaker, displaced
surface low. The ensemble spaghetti plots are extremely messy over
the eastern Pacific and western U.S. so detail confidence remains
quite low. The WPC forecast continued with a solution stronger
than the ECMWF but not as strong as the other guidance.
By Tuesday-Thursday, model agreement has improved regarding the
evolution of the trough and its movement, with the 00Z ECMWF a bit
weaker than its previous runs but clustering better with other
guidance. GFS runs since 00Z have been consistent in showing a
solution similar to what the ECMWF has had, namely a upper low
that closes off in the northern Plains Wednesday and moves into
the Midwest Thursday, and the CMC is similar as well. The track of
the associated surface low is also fairly well clustered for the
late medium range period. Thus models all indicate an impactful
storm system across the central U.S. despite differences in the
exact details.
Trailing flow could bring another system toward the Pacific
Northwest by Wednesday-Thursday, which is now advertised by the
bulk of guidance after previous cycles of the GFS did not show
this feature. Despite better agreement now for a system, timing of
the shortwave track remains questionable.
Better agreement between GFS/ECMWF/CMC deterministic guidance led
to the WPC forecast utilizing a blend of these early in the
period, and even maintained a majority of operational models
through the latter part of the period though phased in some EC and
GEFS ensemble means to temper individual model differences.
...Weather Highlights/Threats...
Early in the period expect the best rain/mountain snow focus to be
over the Pacific Northwest and central West Coast. However the
details of location and intensity are unusually uncertain for a
forecast only 3-4 days out in time as guidance varies widely for
the strength and track of arriving low pressure. Lighter activity
should prevail eastward through the northern Rockies. Then some
moisture should extend southward into the Sierra Nevada, with rain
and mountain snow extending across central and possibly some
southern parts of the West. By Tuesday the southern Montana into
Colorado Rockies and north-central High Plains should begin to see
a favorable combination of upper trough dynamics and low level
upslope flow that would increase precipitation over those areas,
with the High Plains possibly seeing some springtime snow in
addition to the Rockies. Potentially strong low pressure that may
track from the Plains into the Upper Midwest would extend snow
farther northeast across the northern tier along with strong
winds. Meanwhile in the warm sector, there will be increasing
coverage and intensity of rainfall over the eastern
Plains/Mississippi Valley with the establishment of moist low
level flow from the Gulf of Mexico. Persistence of the Gulf inflow
could lead to a couple days or so with a heavy rain threat over or
near the Lower Mississippi Valley. Also the Storm Prediction
Center is monitoring the potential for severe weather over some
southern areas in the central U.S. Check their latest outlooks for
more information. Farther north, a front draped over the Midwest
could also provide a focus for rainfall though likely with lower
totals given less moisture/instability. Lack of confidence in some
specifics of eastern Pacific/western U.S. flow maintains the
potential for some changes in the above most likely scenario.
Colder air moving into the West will initially bring highs down to
as much as 10-20F below normal over the Northwest/northern Rockies
as of Sunday. An area of minus 10-25F anomalies for highs should
then reach into the Intermountain West, Rockies, and
northern-central Plains by next Tuesday-Wednesday. The northern
half of the Plains should still see highs around 15-20F below
normal on Thursday. Sunday should provide the best potential for
some locations in the Northwest to see max temperatures near or
below current record cold highs but Monday could still produce a
few lingering records. Meanwhile most of the eastern half of the
country should trend from mostly below normal temperatures (minus
5-15F anomalies) on Sunday, and potential for a late frost across
parts of the southeastern quadrant of the country, to mostly above
normal readings (plus 5-15F anomalies for highs and perhaps
slightly warmer for morning lows) spreading from west to east
after the weekend. However confidence is lower for exact
temperatures over the northern half of the East due to uncertain
position of a front during the first half of next week.
Tate/Rausch
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