Prognostic Meteorological Discussion
Issued by NWS

000
FXUS02 KWBC 250657
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Thu Apr 25 2024

Valid 12Z Sun Apr 28 2024 - 12Z Thu May 02 2024

***Severe thunderstorms and heavy rain expected for the Plains and
 Midwest Sunday into Monday***


...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 Rockies. A strong
shortwave ejecting across the Central Plains will spur surface
cyclogenesis and multiple rounds of heavy rain and strong/severe
thunderstorms, mainly from central Texas to Iowa/Missouri. Very
warm conditions for this time of year are expected for the eastern
half of the U.S. going into the beginning of next week, and colder
temperatures out West will support some lingering snow for the
higher terrain of the Colorado Rockies. A second trough is then
likely to develop along the West Coast by the middle to end of the
next week with the ridge axis building across the Plains.


...Guidance/Predictability Assessment...

The 00Z model guidance suite features good overall agreement across
the U.S. on Sunday with similar timing on the main shortwave across
the central High Plains, so a multi-deterministic model blend
works well as a starting point in the forecast process. Greater
differences are apparent across the Northern Rockies and Dakotas by
Tuesday, with the 00Z ECMWF trending stronger with an upper low
tracking near the Canadian border. By Wednesday, the 00Z ECMWF
becomes more out of line with the consensus and the machine
learning models with the upper low/trough near the Pacific
Northwest, so the GFS and GEFS mean serve as a better depiction
here. There is also disagreement on the timing of a trough and cold
front across the Great Lakes and Northeast by the end of the
forecast period Thursday, with the CMC/GFS faster and the ECMWF
slower. The use of the ensemble means accounted for about half of
the forecast blend by next Thursday. The QPF forecast started
with about 50% NBM and 1/6 each of the GFS/ECMWF/CMC through
Monday, and then trending to about 2/3 NBM and removing the CMC
for Tuesday and Wednesday.


...Weather/Hazards Highlights...

The overall synoptic environment will be quite conducive for
multiple episodes of excessive rainfall across portions of the
central and lower Mississippi River Valley. There will likely be
multiple mesoscale convective systems that develop from the
ArkLaTex region to Missouri, and there is a good chance of
training convection given the slow overall progression of the
frontal boundary and parallel flow to the trailing frontal
boundary. For the Day 4 period Sunday, the existing Slight Risk
area from the previous Day 5 will be expanded to include more of
eastern Texas where the QPF signal in the GFS/ECMWF has increased.
There is now a multi- model signal for some 3-5 inch totals where
storms train over the same areas, with locally higher totals
possible. There is still a good chance for a future upgrade to
Moderate Risk for portions of this region if these model trends
continue. The WPC forecast for QPF remains on the lower end of the
guidance spectrum given the influence from the NBM. A Slight Risk
area is also planned on Day 5 centered over northern Louisiana and
into portions of adjacent states, generally southeast of the Day 4
outlook area. The convergence boundary is likely to linger across
the region on Monday and fire new rounds of convection, followed by
an abatement in the coverage and intensity of the convection going
in Tuesday over this region.

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 on the Day 4 outlook. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in continuing
snow showers for the higher mountain ranges of Wyoming and
Colorado, although becoming lighter. Rain and mountain snow is also
likely to make a return to the Pacific Northwest for the beginning
to middle of next week as the next shortwave trough arrives. By
Wednesday, showers and storms could once again increase in coverage
from Texas to the Central Plains.

Temperatures will also be making weather headlines as a major
warm-up is expected for a wide expanse 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. Overnight
lows will also be summer-like with lows only falling into the 60s
for many of these same areas. A modest cool-down is likely by mid-
week from the Great Lake to the Ohio Valley and Northeast, and
still remaining warm and humid across the south-central U.S. to the
Carolinas. The opposite holds true for the Intermountain West on
Sunday 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











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