Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
231 AM EDT Thu Apr 21 2022
Valid 12Z Sun Apr 24 2022 - 12Z Thu Apr 28 2022
...Significant late season winter storm this weekend along with
potentially heavy rainfall over portions of the Southern Plains
and Mid-MS River Valley...
...Weather Pattern Overview...
An amplified flow pattern is expected to start the period as the
Northern Plains deep low lifts into Canada while a strong
Southeast ridge extends northward through much of the eastern
U.S.. The associated trailing cold front southward could bring a
localized heavy rainfall threat Sunday into Monday over portions
of the Southern Plains to the Ozarks and Mid Mississippi Valley.
By Tuesday-Wednesday, gradual progression of the mean pattern will
bring moderate upper troughing to the East, a ridge to the
Rockies/Plains, and a trough into the eastern Pacific/West Coast.
Much below normal temperatures may persist for a while over the
far northern parts of the Plains while well above normal readings
are possible over a majority of the eastern half of the country
through the weekend.
...Model Guidance Evaluation...
This forecast cycle the model agreement remains fairly clustered
and agreeable aside from the CMC and to some degree the UKMET
which were slower with the progression of the trough axis moving
from the northern tier toward the Northeast. The ECMWF continued
to be the best proxy through the period as the GFS was on the
faster side of the model spread but overall the GFS/ECMWF show
fairly good agreement through much of the forecast period such
that higher weights of the two were included in the forecast blend
this cycle. How the northeast closed low evolves mid to late week
is still uncertain and the timing of the next system in the
Northwest has continued uncertainty but through day 6-7, the
deterministic runs offered enough value to be considered. To
maintain some continuity, the ECENS/GEFS means were included days
5-7.
...Sensible Weather/Threats...
The strong/significant winter storm affecting the Northern Plains
will be continuing at the start of the medium range with the
surface low likely to be centered across northern Minnesota. Wrap
around precipitation underneath the closed low will likely
continue snow showers and with a strong/tight pressure gradient,
strong winds will likely continue blowing snow and reduced
visibility at times. Conditions improve by early next week as the
low weakens more into southern Canada. Meanwhile, further south,
the trailing cold front slows and stalls over portions of the
Southern Plains to Mid-Mississippi River Valley. Southerly flow
ahead of it will draw up warm, moist air that intersects the
boundary. An increasing 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/northwest
Arkansas into southern/southwest Missouri. The Day 4 Excessive
Rainfall Outlook Slight Risk was maintained this cycle with minor
adjustments based on the latest model trends which showed a nudge
to the south/southeast for the heavy rain axis. Stream flows and
precipitation anomalies are above normal for much of the Slight
Risk area due to recent heavy rainfall and there is potential for
additional rainfall leading up to Day 4. Guidance is still in the
process of resolving the timing and wave details of the surface
front so changes in the most likely coverage and magnitude of
rainfall totals are certainly possible. The front then begins to
accelerate with a progressive and amplified trough axis swinging
through - this will spread lighter rainfall across much of the
eastern U.S. during the Tuesday through Wednesday period.
Generally unsettled weather but light precipitation will spread
across the northern portions of the Pacific Northwest next week as
a series of shortwaves move through the flow underneath a closed
upper low positioned off British Columbia. Timing and specific
details are still uncertain in the lower confidence weather
pattern but overall several opportunities for precipitation though
at this time nothing looks too significant.
The weekend storm system will bring both much above normal and
much below normal temperatures to portions of the CONUS Sunday
through the middle of next week. Ahead of the system, expect
seasonably warm temperatures across the eastern U.S., especially
Sunday high temperatures across the eastern Great Lakes where
highs could top 20 degrees above normal. Warm temperatures
continue Monday but to a lesser degree. The exception to the
eastern warmth is for the coastal Northeast areas and perhaps into
the Mid-Atlantic where surface high pressure present 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
temperatures forecasting over the region. The West will see more
variable temperatures, with minus 5-15F anomalies over the
Intermountain West/Rockies late in the weekend followed by a
west-to-east warming trend with increasing coverage of above
normal readings. Warmest highs of 10-15F above normal are likely
to extend from the Great Basin/Southwest into the central High
Plains during Tuesday-Wednesday. At the same time
clouds/precipitation ahead of the upper trough nearing the West
Coast may bring slightly below normal highs to the Pacific
Northwest.
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
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