Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Thu Apr 21 2022
Valid 12Z Sun Apr 24 2022 - 12Z Thu Apr 28 2022
...Significant late season winter storm affecting the northern
tier into Sunday along with potentially heavy rainfall over
portions of the Southern Plains and Mid Mississippi Valley...
...Weather Pattern Overview...
An amplified flow pattern will exist early in the period
Sunday-Monday as the Northern Plains/Upper Midwest deep low lifts
into Canada while a strong Southeast ridge extends northward
through much of the eastern U.S. The storm system's associated
trailing cold front could bring a heavy rainfall threat over
portions of the Southern Plains to the Ozarks and Mid Mississippi
Valley. Most guidance expects gradual progression of the mean
pattern with time, ultimately leading to troughs near each coast
and a broad central U.S. upper ridge. Both troughs could contain
an embedded upper low. Much below normal temperatures may persist
for multiple days over the far northern parts of the Plains while
well above normal readings are possible over the East during
Sunday-Monday and over the Great Basin/Southwest into parts of the
Plains by Tuesday-Thursday.
...Model Guidance Evaluation...
Overall a consensus/average of 00Z and 06Z models early in the
period followed by a blend of models and 06Z GEFS/00Z ECMWF means
provided a reasonable depiction of the most likely forecast
scenario through the period. Guidance still exhibits some spread
for the departing northern tier storm, again with the GFS fastest
and CMC slowest, while the ECMWF continues to provide the most
consistent intermediate solution. Clustering is gradually
improving though. Differences for the trailing upper trough
crossing the central-eastern U.S. during the first half of the
week have come down to mainly low-predictability detail issues.
Meanwhile there is good agreement that energy from the initial
northern tier upper low will continue northeastward through
Canada, while trailing energy crossing the Great Lakes and
southeastern Canada develops an upper low that reaches New England
by early next Thursday. Latest models and means show better than
average clustering for this potential upper low relative to
typical day 7 forecasts, with associated low pressure tracking
close to the New England coast.
On the other hand, models and individual ensemble members continue
to show a lot of spread for specifics of individual shortwaves
within the mean trough whose axis settles over the eastern
Pacific/West Coast from about Tuesday onward. These differences
affect the forecast of coverage/amounts of precipitation over the
West and eventually the surface pattern as far east the Plains by
day 7 Thursday. By late in the period the main theme of
models/means is to keep the upper trough axis closer to the West
Coast than the past three ECMWF runs through 00Z. Most new 12Z
model runs are still within the majority cluster while the ECMWF
has adjusted closer to consensus.
...Sensible Weather/Threats...
The strong/significant winter storm affecting the Northern Plains
will be ongoing at the start of the medium range period with the
surface low likely tracking across northern Minnesota on Sunday.
Wraparound precipitation underneath/around the closed upper low
will likely continue snow showers, and a strong/tight pressure
gradient should produce strong winds that would continue blowing
snow and reduced visibility at times. Conditions improve by early
next week as the low weakens and tracks over southern Canada.
Meanwhile to the south, the trailing cold front will intersect
with warm/moist air from the Gulf and a strengthening low level
jet Sunday night into Monday morning should focus a few mesoscale
convective systems that have the potential to train and repeat
over the same areas. The latest forecast guidance suggests
potential for multi-inch totals during the Day 4 period (ending
12Z Monday April 25) across an area from northeastern Texas
through eastern Oklahoma, western/northern Arkansas, southern
Missouri, and perhaps extending a little east from there. The Day
4 Excessive Rainfall Outlook maintained a Slight Risk area
highlighting this region with only slight refinements for new
guidance. Stream flows/soil moisture/precipitation anomalies are
above normal for much of this area due to recent heavy rainfall.
Guidance is still in the process of resolving the timing and wave
details of the surface front so additional refinements in the most
likely coverage and magnitude of rainfall totals are certainly
possible. The front should accelerate as it continues eastward so
rainfall across the eastern U.S. should be lighter during
Tuesday-Wednesday. By Wednesday-Thursday the upper low forecast to
approach/reach New England and associated low pressure could focus
some precipitation over the region, with coverage and amounts
sensitive to the exact track of the system. A portion of this
precipitation could be snow in the higher elevations. Unsettled
weather with generally light to moderate precipitation will spread
across areas from the northern half of the West Coast into the
northern Rockies as a series of shortwaves move through the mean
trough south of a closed upper low positioned off British
Columbia. Timing and coverage with each episode of rain/high
elevation snow will take additional time to resolve given the
typical lower predictability of medium to smaller scale of
features contained within the mean flow.
The weekend storm system and flow on either side of the associated
cold front will bring contrasting temperature extremes to the
central and eastern states into early next week. Northern
Plains/Upper Midwest areas will see unseasonably chilly readings
with highs up to 20-30F below normal while more moderate below
normal anomalies will spread across the rest of the central U.S.
Areas near the Canadian border may stay below normal through
Thursday. Ahead of the cold front, expect many areas to see
temperatures 5-20F above normal and potentially even warmer
anomalies for morning lows over the Great Lakes on Sunday. The
exception to the eastern warmth should be for the coastal
Northeast areas and at times into the Mid-Atlantic where surface
high pressure may keep temperatures on the cooler side. A front
meandering to the south could lead to a sharp contrast between
cool air to the north and warmth to the south and west, increasing
the challenge of temperature forecasting over the region.
Through the period a warming trend will spread across the southern
two-thirds of the West and into the central/southern Plains with
plus 10-20F anomalies for highs becoming common by
Tuesday-Thursday. In contrast, the upper trough nearing the West
Coast will support slightly below normal highs from the Pacific
Northwest/northern California into the northern Rockies Tuesday
onward. The upper trough and possible embedded upper low reaching
the eastern U.S. should lead to below normal readings over the
region by midweek with the Great Lakes into central Appalachians
being the most likely area to see highs 10-20F below normal for
one or more days.
Rausch/Taylor
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 Middle/Lower Mississippi
Valley, the Southern Plains, the Ohio
Valley, and the Tennessee Valley, Sun, Apr 24.
- Flooding possible across portions of the Central Plains, the
Upper/Middle Mississippi Valley, the
Upper Mississippi Valley, and the Northern Plains.
- Flooding occurring or imminent across portions of the Southeast
and the Lower Mississippi Valley.
- High winds across portions of the Central Plains, the
Upper/Middle Mississippi Valley, and the
Northern Plains, Sun, Apr 24.
- Much below normal temperatures across portions of the Upper
Mississippi Valley and the Northern
Plains, Sun-Tue, Apr 24-Apr 26.
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