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000
FXUS02 KWBC 240656
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Wed Apr 24 2024

Valid 12Z Sat Apr 27 2024 - 12Z Wed May 01 2024

***Severe thunderstorms and heavy rain expected for the Plains and
 Midwest over the weekend***


...General Overview...

An amplified upper level flow pattern is forecast to be in place
across the Continental U.S. this weekend, with a building ridge
across the East and a trough across the West. Multiple shortwave
ejecting across the Plains will spur surface cyclogenesis and
multiple rounds of heavy rain and strong/severe thunderstorms,
mainly from central Texas to Iowa/Missouri. A pronounced warming
trend is expected for the eastern half of the U.S. going into the
beginning of next week, and colder temperatures out West will
support late season snowfall for the higher terrain of the Central
and Northern Rockies. A second trough is then likely to develop
along the West Coast by the middle to end of the next week.


...Guidance/Predictability Assessment...

The 00Z model guidance suite features good overall agreement across
the U.S. on Saturday with similar timing on both of the main
shortwave troughs across the western High Plains and Upper Midwest,
so a multi-deterministic model blend works well as a starting point
in the forecast process. The 00Z CMC becomes a little slower with
the trough ejecting east across the Central Plains by Sunday, but
otherwise the guidance is close in most aspects. Recent runs of the
CMC have differed more across the northwestern U.S. going into the
Monday-Wednesday time period, especially with the 12Z CMC that was
much faster bringing the shortwave inland compared to the model
consensus, so the fronts/pressures was based on the better
clustered GFS/ECMWF and their ensemble means for the latter half of
the forecast period. The QPF forecast started with about 50% NBM
and 1/6 each of the GFS/ECMWF/CMC through Sunday, and then trending
to about 2/3 NBM and removing the CMC Monday and Tuesday.


...Weather/Hazards Highlights...

The overall synoptic environment will be increasingly conducive for
episodes of excessive rainfall across portions of the
central/southern Plains and into portions of the Midwest states
over the weekend. There will likely be multiple mesoscale
convective systems that develop from central Texas to Missouri, and
there is a good chance of training convection given the slow
overall progression of the frontal boundary and nearly
unidirectional flow through the lower to middle troposphere. For
the Day 4 period Saturday, the existing Slight Risk area from the
previous Day 5 will be expanded to include parts of north-central
Texas where the QPF signal in the GFS/ECMWF has increased, with a
MCS likely to develop. There will likely be another MCS across
eastern Kansas into western Missouri, and both with rainfall rates
reaching two inches per hour with some storms. The core of the
heaviest rainfall should slowly progress eastward for the Day 5
period Sunday across the ArkLaTex region and into southern
Missouri, where a Slight Risk area is planned with a multi-model
signal for some 2-4 inch totals where storms train over the same
areas. There is a good chance that portions of both outlook areas
may eventually need a Moderate Risk in later forecast updates if
the QPF signal continues to remain robust, so this will continue to
be closely monitored.

Elsewhere across the U.S., widespread moderate to locally heavy
rain is expected from Minnesota to northern Michigan on Sunday as
the surface low lifts northeastward, and a Marginal Risk area is
planned to account for that. Another area of enhanced rainfall is
also probable over northeastern Colorado and portions of adjacent
states, where a Marginal Risk remains valid for Saturday. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in several
inches of snow for the higher mountain ranges. Rain and mountain
snow is also likely to make a return to the Pacific Northwest for
the middle of next week as the next shortwave trough arrives.

Temperatures will also be making weather headlines as a major
warm-up is expected for most of the country east of the Rockies.
Highs are expected to rise well into the 80s from the
Central/Southern Plains to the Ohio Valley and then reaching the
East Coast by Monday, perhaps reaching 90 degrees in some cases.
These readings are on the order of 10-20 degrees above normal for
late April, and there may be some daily record highs set. The
opposite holds true for the Intermountain West this weekend with
readings 5-15 degrees below average, before things moderate going
into early next week.

Hamrick

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







$$