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000
FXUS02 KWBC 221858
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Mon Apr 22 2024

Valid 12Z Thu Apr 25 2024 - 12Z Mon Apr 29 2024

...Severe thunderstorms and heavy rain possible for the Plains and
Mississippi Valley late this week and again this weekend...


...Overview...

The upper level pattern will be fairly amplified and progressive as
a couple of shortwaves/embedded upper lows progress west to east
across the country. Initial troughing over the East Thursday-
Friday will be replaced with strong ridging this weekend which
should help steer system northward into the Upper Midwest/Great
Lakes. This overall pattern will support rounds of active, and
potentially hazardous, weather across portions of the Plains and
Mississippi Valley, and a prolonged period of unsettled weather
for the West with rain at low elevations and snow at high
elevations. Ridging over the East Coast will keep the weather calm
through most of the period, but a cold front will move towards the
Northeast over the weekend, bringing precipitation back to the
region.


...Guidance/Predictability Assessment...

The models continue to show good agreement on the large scale upper
pattern during the medium range period, but plenty of disagreement
in the details still. There are some minor timing differences with
the first shortwave as it lifts through the Central U.S. Thursday-
Friday, but a general blend of the latest deterministic models
seemed to provide a good starting point. Also plenty of timing
uncertainties with the second shortwave early next week. As of the
00z/06z models, the CMC was faster with this shortwave than the
other guidance and so the late period WPC blend for today was based
on a non-CMC compromise, including the latest ensemble means with
the GFS/ECMWF. However, there is a faster trend in the new 12z
guidance suite that came in after forecast generation time, so
this will need to be watched. Overall though, good consistency was
maintained between the overnight and the new day shift progs.


...Weather/Hazards Highlights...

Thursday and Friday, an upper level shortwave will move northeast
across the Central U.S. and will be accompanied by a surface low
pressure system. Low pressure will strengthen over the Central
Plains on Thursday, then the system will move towards the Upper
Midwest on Friday, pulling a warm front north across the south-
central and eastern U.S. and a trailing cold front from the Mid-
Mississippi Valley to the Southern Plains. This system is forecast
to produce showers and thunderstorms over portions of the Plains
and Mississippi Valley, and the ingredients (instability and
moisture) will be in place for locally heavy rainfall totals. A
Marginal Risk area remains in place over portions of the Central
Plains and Mid-Mississippi Valley in the vicinity of the developing
surface low in the Day 4 (Thursday) ERO, but dry antecedent
conditions may limit the overall threat. Precipitation will become
more widespread on Friday, and another Marginal Risk continues for
much of the Mississippi Valley and eastern portions of the Plains
in the Day 5 (Friday) ERO. In addition to heavy rainfall, severe
thunderstorms will be possible ahead of a dryline in the warm
sector of this system, and the Storm Prediction Center has
highlighted portions of the Plains and Mississippi Valley in the
Severe Weather Outlook for Thursday-Friday. On the western side of
the dryline, strong winds and low humidity will create an
increased wildfire risk for portions of New Mexico, west Texas, the
Texas and Oklahoma panhandles, and far southeastern Colorado.

Over the weekend, the second upper level shortwave will move
northeast across the Central U.S. and create a precipitation
pattern that will look very similar to the first system. A low will
strengthen over the Central/Southern Plains Saturday and move
towards the Upper Midwest Sunday into Monday, bringing another
round of showers and storms to portions of the Plains and much of
the Mississippi Valley. Precipitation chances will also spread into
the Ohio Valley and Northeast over the weekend as the leading
system moves over the top of the East Coast ridge. Again,
increasing threats for severe weather per the Storm prediction
Center which has an area highlighted on Saturday across parts of
the southern/central Plains. The southern portion of the cold front
associated with this feature may stall early next week, and
increase heavy rain chances again across portions of the central
Gulf Coast.

In the West, mean upper troughing will allow precipitation chances
to persist across much of the region through the end of this week,
but drier conditions will likely develop over the Southwest on
Sunday and Monday. Precipitation will fall as rain at lower
elevations and as snow at higher elevations. Daily high
temperatures will likely remain slightly below normal across the
West, but highs may return to near normal in the Southwest Sunday
and Monday after precipitation comes to an end.

Temperatures will trend above normal across much of the south-
central and eastern U.S. as a warm front lifts north later this
week, and high temperatures will likely reach the 70s and 80s for
much of these regions. Highs could reach the 90s and potentially
over 100 degrees for portions of south Texas by Saturday.


Santorelli/Dolan


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 forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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
https://www.wpc.ncep.noaa.gov/#page=ovw




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