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FXUS21 KWNC 231917

PMDTHR

US Hazards Outlook

NWS Climate Prediction Center College Park MD

300 PM EDT April 23 2024



SYNOPSIS: A persistent pattern featuring a long-wave mid-level low pressure 

over western North America and mid-level high pressure farther east is expected 

to support episodes of heavy rainfall across the central Contiguous United 

States (CONUS) through the middle of week-2, with a slight risk for episodes of 

high winds for much of the Southwest, Rockies, and Great Plains. The timing and 

magnitude of individual episodes of heavy rain and high wind are uncertain at 

this time, but the greatest risk for heavy precipitation is anticipated for 

parts of the Southern and Central Plains and Middle Mississippi Valley early in 

the period, thus a moderate risk is designated. The forecast episodes of heavy 

rain are expected to occur over an area expecting very heavy precipitation 

prior to week-2, supporting an increased risk of  flooding across parts of the 

central and southern Great Plains and much of the Mississippi Valley.



HAZARDS



Moderate risk of heavy precipitation for portions of the Southern and Central 

Plains and Middle Mississippi Valley, Wed-Fri, May 1-3.



Slight risk of heavy precipitation for much of the northern Rockies and High 

Plains, Great Plains, the Mississippi Valley, the Upper Midwest, and the Lower 

Ohio Valley, Wed-Sun, May 1-5.



Slight risk of high winds for much of the Southwest, Rockies, and Great Plains, 

Wed-Sun, May 1-5. 



Flooding possible for parts of the Central and Southern Plains, Mississippi 

Valley, and Ohio Valley.



DETAILED SUMMARY



FOR FRIDAY APRIL 26 - TUESDAY APRIL 30: 

https://www.wpc.ncep.noaa.gov/threats/threats.php



FOR WEDNESDAY MAY 01 - TUESDAY MAY 07: The GEFS and ECMWF ensemble means are in 

good agreement indicating a fairly stagnant pattern featuring a 

moderately-amplified mean 500-hPa long-wave trough over or near western North 

America, and a downstream mid-level ridge with an axis over the eastern CONUS. 

The Canadian ensemble mean shows a more progressive pattern, but has shifted 

toward the solutions of the GEFS and ECMWF ensemble means, reloading the 

mid-level trough near the West Coast late week-2 as the initial mid-level 

trough moves into the central CONUS and dissipates. This boosts confidence in 

the favored solution relative to yesterday. Unlike yesterday, both the 0Z ECMWF 

ensemble mean and 6Z GEFS mean show weakening features late in the period, but 

hinting that conditions may re-amplify beyond the week-2 period.







The persistent mid-level trough in the West favors a southerly surface flow 

bringing unusually moist air northward into the central CONUS, where 

cyclonically-curved divergent flow aloft is expected. This combination puts a 

large part of the central CONUS at increased risk for one or more episodes of 

heavy precipitation and localized thunderstorms. This quasi-stationary pattern 

is expected to change little until weakening later week-2, keeping a slight 

risk of heavy precipitation in place through the early and middle parts of the 

period, May 1-5. Probabilistic Extremes Tools (PETs) from the GEFS and the 

European ensembles have come into better agreement today, with both showing 

enhanced odds for 3-day precipitation totals above both the one-inch and 

85th-percentile thresholds in a swath from central Texas northeastward into 

western parts of the Middle Mississippi Valley during the first 3 days of 

week-2 (Wed-Fri May 1-3), supporting a moderate risk for heavy precipitation.







The heavy precipitation and thunderstorm activity anticipated during week-2 is 

not expected to be as intense as conditions in the short-term, but will 

exacerbate impacts related to excessive precipitation. The combined effects of 

two weeks of excessive precipitation support a flood risk near and downstream 

from areas where the greatest rainfall totals are expected, this includes much 

of  the south-central Great Plains and much  of the Mississippi Valley 

according to the GEFS and ECMWF ensemble means. Runoff from heavy rainfall is 

expected to enhance the flood risk farther to the south and east (downstream) 

across the Lower Mississippi Valley.







The anticipated long-wave pattern also favors cyclogenesis near or to the lee 

of the Rockies, with higher surface pressures forecast farther east and west. 

The timing and strength of any surface low pressure system that forms is 

uncertain, so a large area from the Southwest and the Rockies eastward through 

the central Great Plains has a slight risk for one or more episodes of high 

winds for May 1-5 until conditions ease later week-2. 



  



Farther north, models generally favor below normal 500-hPa heights across 

Alaska, with a trough axis near or west of the Mainland that favors stormy 

weather near the coast of south-central and southeastern Alaska. This pattern 

may support one or more periods of enhanced precipitation and winds, but 

conditions are not expected to reach hazardous criteria precluding associated 

hazards from being designated.



FORECASTER: Rich Tinker 



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