Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
309 AM EDT Sun Mar 20 2022
Valid 12Z Wed Mar 23 2022 - 12Z Sun Mar 27 2022
...A strong low pressure system will continue to cause
precipitation in the eastern U.S. midweek, with severe storms in
the Southeast, locally heavy rain, and wintry weather across the
northern tier...
...Overview...
The most active weather during the medium range period will be
around midweek, as a potent upper low and a surface low pressure
system track from the Mid-Mississippi Valley to the Great Lakes
region. Rain is forecast to spread ahead of the associated cold
front with some embedded heavy totals, while severe thunderstorms
are possible in the Southeast. Meanwhile on the cold northern side
of the system, springtime snow and mixed precipitation are
possible from the Great Lakes region to the interior Northeast. As
a ridge builds into the West, warm temperatures including some
possible record highs particularly for California are forecast.
The upper level pattern looks to stagnate over the weekend with an
East Pacific trough, Intermountain West ridge, and eastern U.S.
trough, which will lead to overall dry conditions.
...Guidance Evaluation/Predictability Assessment...
Model guidance from the 12/18Z yesterday cycle continues to agree
with a potent rounded upper low in the central U.S. supporting a
surface low over the Middle Mississippi Valley day 3/early Wed.
These features should move northeastward Thu, but with some model
differences on the upper-level feature staying closed or opening
up. The WPC forecast leans toward a solution with the low
remaining closed, favoring the ECMWF/CMC and their means. The
GFS/GEFS guidance shows a more open pattern by that time, but the
main outlier for the 12Z cycle appeared to be the UKMET, with a
more strung out trough holding back more energy into northern
Mexico than current consensus, looking like some guidance from
previous cycles but it is now one of the main holdouts. Then by
Friday it separates northern and southern stream energy with the
northern stream tracking likely too quickly. Other than the UKMET,
despite the differences in timing of phasing, the progression of
the trough/low eastward is mostly more agreeable. Models have
stuck with the trend for an occluded surface low spreading more
precipitation on the northwestern side.
By around day 5/Fri and beyond, the troughing should slowly lift,
though additional energy digs from the north to reinforce
troughing across the East through the weekend, with some typical
differences in shortwave energies and thus timing for cold fronts
and low pressure systems. Namely, ensemble guidance generally
showed low pressure near Maine or the Canadian Maritimes around
Sat, but the 12/18Z deterministic guidance showed a local high
around there with lows north and south. The 00Z guidance seems to
be more in line with the ensemble consensus. Meanwhile there is
rather good consensus for periods of ridging in the West with its
axis shifting slowly eastward late in the week. Shortwaves moving
across the Northwest could suppress the northern side around
Thu-Fri, but most guidance other than the CMC has the ridge
rebuilding for the weekend. The incoming 00Z suite of guidance
shows a similar pattern but with typical wiggles in the details.
The WPC forecast was based on an initial blend of the 12Z ECMWF,
12/18Z GFS, and 12Z CMC, just excluding the UKMET in terms of the
deterministic models. Ensemble mean guidance was phased in around
day 5 and increased somewhat through days 6-7, but only to about
40 percent given fairly good agreement for the large scale pattern
even in the ECMWF/GFS in particular.
...Weather Highlights/Threats...
Another rainy day is expected as the medium range period begins
Wednesday as ample Gulf of Mexico moisture flows into the low
pressure system tracking across the central U.S. Storms could be
severe across the Deep South down to the central/eastern Gulf
Coast per the Storm Prediction Center. Furthermore, widespread
rain is likely across the East, which could potentially cause some
isolated flash flooding in some areas from the southern/central
Appalachians eastward. North and west of the low track, snow and
wintry precipitation are possible, with the highest probabilities
for notable snow in the Upper Great Lakes region. Wintry mix or
snow could also occur particularly in higher elevations of the
interior Northeast north of a warm front on Wednesday-Thursday and
as a western Atlantic low develops by early Friday. Showers could
linger into late week across the East with generally light amounts
expected, but perhaps with more moderate amounts as a front
lingers in Florida, which could cause localized flooding issues if
rain falls atop saturated soils. A mainly dry pattern is expected
for the western and central U.S. for the latter part of the week,
though with some Pacific Northwest and Northern Rockies light
precipitation possible before a more widespread moisture surge
next weekend.
The strong upper ridge building into the West will lead to a broad
area of highs 10-20F above normal Wednesday-Sunday with slightly
higher localized anomalies possible. There is potential to reach
daily record highs across California Wednesday to Friday and
spreading eastward into the Intermountain West and Southwest as
the ridge axis shifts east. Leading upper level troughing should
support temperatures 10-20F below average across the
central/southern High Plains Wednesday. The cooler air should
moderate closer to normal by the latter part of next week as it
progresses eastward. Ahead of the trough and cold fronts,
generally warmer than normal conditions are likely across much of
the eastern third of the U.S. for much of the week, transitioning
to near normal temperatures by Friday and Saturday and a cooldown
associated with a secondary cold front in the Great Lakes by
Sunday. Isolated record highs are possible over parts of Florida
Tuesday-Wednesday.
Tate
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
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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml