Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Fri Apr 08 2022
Valid 12Z Mon Apr 11 2022 - 12Z Fri Apr 15 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 across the South...
...Overview...
The latest guidance continues to support an amplified and active
weather pattern across the lower 48 next week. A reinforced
western U.S. trough should finally emerge into the Plains by
around midweek and a vigorous low pressure system will develop
over the Plains/Upper Midwest. This is likely to bring an array of
significant weather across the CONUS, including heavy snow in some
higher elevations of the West early in the workweek, which is
expected to spread north and west of the surface low track into
northern/central parts of the Plains around midweek. In the warm
sector of the system, severe weather and heavy rain are likely in
southern/central parts of the Plains and Mississippi Valley and
potentially eastward. By late week, the closed upper low may begin
to lift due to amplified ridging in the western Atlantic, while
additional (likely less amplified) troughing enters the West
around Friday/day 7.
...Guidance Evaluation/Predictability Assessment...
Though model guidance is united in showing the developing western
trough becoming a closed upper low as it tracks into the central
U.S., ample differences remain with the timing and track of the
upper and surface low features. As the period begins Monday, GFS
runs from the 00/06Z as well as the 12Z model cycle remain
strongest with the initial shortwave over the Upper Midwest
compared to other guidance, affecting frontal position. Meanwhile
most guidance continues to show a small closed upper low near the
Pacific Northwest, though the ECMWF has been weaker but may have
strengthened a bit with the 12Z run. This also impacts the
strength and position of an associated surface low; the 12Z CMC
may be a good compromise between the stronger and farther north
GFS runs and weaker and farther south ECMWF runs.
Going into Tuesday and beyond, the initial shortwave differences
grow quickly and affect the main trough/low's axis and extent
southward. The GFS runs have remained the quickest and farthest
north with the developing upper low, while the EC has been
consistently deeper and slower. The CMC clusters better with the
ECMWF, and each model's ensemble members tend to cluster near its
deterministic run without considerable overlap. These differences
with the trough/low are also influenced by additional upstream
energy diving south from the Arctic/Alaska/northwestern Canada, a
low predictability feature that also shows quite a bit of
variability among guidance. The WPC forecast continued to favor a
slower solution with the upper low, more like the EC/EC
mean/CMC/CMC mean compared to the faster GFS/GEFS, considering
continuity as well as typical model biases. Perhaps by around day
6/Thursday or so, the ECMWF and CMC may be a bit too slow in
lifting the surface low out, but it should be a wrapped up system
so it is possible.
Farther upstream, there is considerable variability with the flow
behind the main low, with potential for a bout of low amplitude
ridging in the central U.S. late week (though this is particularly
seen in the GFS suite that was not favored) before another system
may enter the West. The ensemble means provided a fair starting
point for this uncertain flow pattern.
...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 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 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,
possibly creating blizzard conditions. 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 should lead to a couple days or so
with a heavy rain threat over or near the Lower Mississippi Valley
with some potential for flash flooding. Also the Storm Prediction
Center is monitoring the potential for severe weather over parts
of the Plains and Mississippi Valley. Check their latest outlooks
for more information. The pattern certainly suggests a heavy
rain/severe weather/wintry weather threat, but details on where
these hazards occur and when remains uncertain still, with plenty
of forecast refinements to come.
The western U.S. should see several days of below normal
temperatures, with daytime highs 20+ degrees below normal shifting
eastward Mon-Wed. Some moderation is likely by later in the week
across the West, though still below normal with additional
troughing moving in. By next Thursday-Friday, the core of the cold
should be over the northern Plains with low temperatures 10-20F
below normal and highs even approaching 30F below average.
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.
Tate/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
Hazards:
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Middle Mississippi Valley, the Southeast,
the Southern Plains, and the Ohio Valley, Mon-Thu, Apr 11-Apr 14.
- Heavy snow across portions of California, the Central Great
Basin, the Pacific Northwest, and the Northern Great Basin, Mon,
Apr 11.
- Heavy snow across portions of the Central Rockies, the Central
Plains, the Central Great Basin, the Northern Plains, and the
Northern Rockies, Mon-Tue, Apr 11-Apr 12.
- Heavy snow across portions of the Central Plains, the Upper
Mississippi Valley, and the Northern Plains, Tue-Thu, Apr 12-Apr
14.
- Severe weather across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee Valley, the Middle Mississippi
Valley, the Southeast, the Southern Plains, and the Ohio Valley,
Mon-Wed, Apr 11-Apr 13.
- Flooding possible across portions of the Southeast.
- Flooding occurring or imminent across portions of the Southeast
and the Middle Mississippi Valley.
- Flooding likely across portions of the Southeast.
- Excessive heat across portions of the Southern Plains, Mon-Wed,
Apr 11-Apr 13.
- High winds across portions of the Central Plains, the Central
Rockies, the Central Great Basin, the Southern Rockies, the
Southern Plains, and the Southwest, Mon-Wed, Apr 11-Apr 13.
- High winds across portions of the Central Rockies, the Central
Plains, the Southern Plains, the Upper Mississippi Valley, and the
Northern Plains, Wed-Thu, Apr 13-Apr 14.
- Enhanced wildfire risk across portions of the Southern Rockies,
the Central Plains, the Southern Plains, and the Southwest,
Mon-Tue, Apr 11-Apr 12.
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