Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Wed Apr 06 2022
Valid 12Z Sat Apr 09 2022 - 12Z Wed Apr 13 2022
...Overview...
Guidance continues to show an amplified but reasonably progressive
upper pattern from the weekend into the middle of next week. A
deepening trough over the West will spread rain/higher elevation
snow and well below normal temperatures across the region, with
the colder air and rain/snow reaching into parts of the northern
and central Plains by early-mid week. Ahead of the upper trough
and associated wavy surface front, moisture flowing northward from
the Gulf of Mexico should promote rainfall of varying intensity
over the eastern Plains/Mississippi Valley next week. Meanwhile a
deep upper trough crossing the East during the weekend will
produce cool weather with showers over some areas. An upper ridge
moving into the region from the central U.S. will bring warmer
temperatures to the eastern half of the country after the weekend.
...Guidance Evaluation/Predictability Assessment...
Confidence remains fairly good for the overall pattern evolution
and most aspects of the departing eastern trough. However in some
respects the forecast for details of the western trough may be
getting more complicated. Timing/evolution differences for energy
initially over the Alaska Panhandle/Gulf of Alaska and forecast to
contribute to a possible upper low within the western trough have
persisted over multiple runs, with some influence on leading
shortwave energy crossing the northern tier U.S. and southern
Canada. Now models/ensembles are also diverging with specifics of
flow over the northeastern Pacific/northwestern North America by
around Monday and this issue has downstream effects on the western
trough by late in the period.
Looking at the 12Z/18Z guidance contributing to the updated
forecast, the 18Z GFS generally trended closer to the
model/ensemble mean average versus the 12Z run for leading flow
across the northern tier U.S./southern Canada and the upper trough
digging into the West. Guidance has become split for timing the
arrival of Gulf of Alaska energy that could form a closed low as
the 12Z UKMET sided with the slower GFS while the ECMWF/CMC were
faster. Toward the end of the period next Wednesday the ensemble
means supported an upper trough progression (its axis reaching the
Rockies/Plains) near an average of the 18Z GFS and somewhat faster
12Z ECMWF. The 12Z CMC had similar timing but with an upper low
track well south of other guidance. Plus its broad upper low
centered over the Alaska Panhandle did not have much support. A
blend of the 18Z GFS and 12Z ECMWF/CMC/UKMET early followed by
trending to the 18Z GFS/12Z ECMWF with their respective ensemble
means provided the most reasonable depiction and continuity for
the western-central U.S. evolution as well as for the departing
eastern U.S. upper trough.
The most dramatic change from the new 00Z guidance is in the CMC.
First it has trended slower with the Gulf of Alaska
energy--joining the GFS/UKMET. This cluster would have a much
stronger surface system reaching somewhere along the northern half
of the West Coast than previously forecast. Then upstream changes
in the CMC lead to a much faster and northward path for the core
of the western upper trough, straying eastward beyond other
solutions over the Plains. In contrast the 00Z ECMWF has
maintained remarkable continuity given the differences and/or
changes in the other models. It did trend just a bit slower,
leading to a day 7 Wednesday trough progression that now matches
the means.
...Weather Highlights/Threats...
The upper trough currently expected to amplify into the West and
approach or reach the Plains by next Wednesday will first bring
rain and higher elevation snow into the Pacific Northwest and
northern Rockies during the weekend. Most totals should be in the
light to moderate range though some localized enhancement is
possible over favored terrain. A more favorable combination of
upper trough dynamics and low level upslope flow should increase
precipitation over the northern-central Rockies and High Plains
during the first part of next week, with the High Plains possibly
seeing some snow in addition to the Rockies. There are still
important uncertainties over the details of the upper trough so
confidence is not great in southward extent and amounts of
precipitation across central/southern parts of the West--and to
some degree over the Rockies/Plains--at this time. There will also
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. Farther east, cold air aloft
associated with the upper trough crossing the East during the
weekend will promote areas of diurnally enhanced showers from the
Ohio Valley/Appalachians into the Northeast especially on
Saturday. Some precipitation could be in the form of snow, with
the best chances across the peaks of the Central Appalachians in
West Virginia.
Colder air moving into the West will initially bring highs down to
as much as 10-15F below normal over the Northwest/northern Rockies
during the weekend. An area of minus 10-20F anomalies for highs
should then reach into the Intermountain West, Rockies, and
northern-central Plains by next Tuesday-Wednesday. Sunday may
provide the best potential for some locations in the Northwest to
see max temperatures near or below current record cold highs.
Meanwhile the eastern half of the country will trend from mostly
below normal temperatures (up to minus 10-20F anomalies Saturday),
and potential for a late frost across parts of the southeastern
quadrant of the country, to mostly above normal readings (plus
5-15F anomalies) spreading from west to east after the weekend.
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