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FXUS21 KWNC 081820

PMDTHR

US Hazards Outlook

NWS Climate Prediction Center College Park MD

300 PM EDT May 08 2024



SYNOPSIS: Early in week-2, a transient area of mid-level low pressure forecast, 

along with continued surface return flow from the Gulf of Mexico sustains the 

risk of heavy precipitation for many parts of the southeastern contiguous U.S. 

(CONUS).  Upstream, building mid-level high pressure over the lower Four 

Corners is expected to bring unseasonably warm temperatures, renewing the risk 

of excessive heat conditions for parts of the Rio Grande Valley. Combined with 

drier than normal conditions and strengthening surface pressure, there is an 

increased risk of high winds which may elevate wildfire potential over the 

southwestern CONUS. Over Alaska, cooler than normal conditions are forecast as 

snowmelt and river ice breakup season is underway.  



HAZARDS



Slight risk for heavy precipitation for portions of the Lower Mississippi and 

Tennessee Valleys, and Southeast, Thu-Fri, May 16-17.



Slight risk for excessive heat for parts of the Southern Plains, Sat-Tue, May 

18-21.



Slight risk of high winds for parts of the Four Corners and western High 

Plains, Fri-Tue, May 17-21. 



DETAILED SUMMARY



FOR SATURDAY MAY 11 - WEDNESDAY MAY 15: 

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



FOR THURSDAY MAY 16 - WEDNESDAY MAY 22: A fairly muted 500-hPa height anomaly 

pattern is featured in both the GEFS and ECMWF total week-2 ensemble means, 

generally consisting of above-normal heights throughout the West and the 

southern tier, with near to weakly below normal heights mostly east of the 

Mississippi. Analysis of the daily 500-hPa height fields show that the 

anomalous mid-level troughing is strongest early in the period over the Plains 

and Mississippi Valley, and gradually deamplifies while lifting out over the 

eastern CONUS towards the end of next week. Along with return flow favored at 

the surface, much of the southeastern CONUS looks to remain wetter than normal 

through mid-May, with the potential for locally heavy precipitation over parts 

of the Lower Mississippi Valley and the Southeast. Surface prognosis charts 

from the Weather Prediction Center (WPC) continue to feature a warm frontal 

boundary draped across the Gulf of Mexico coastline and extending into the 

western Atlantic late in week-1. With this forcing expected to remain 

established heading into week-2, there is fair agreement between the raw GEFS 

and ECMWF mean ensemble depicting enhanced precipitation amounts, with the 

latter being wetter, over the central and eastern Gulf Coast states through day 

9 (May 17). Therefore, a slight risk of heavy precipitation is continued for 

May 16-17 where the Probabilistic Extremes Tool (PETs) guidance shows at least 

a 20% chance for 3-day amounts exceeding the 85th percentile and 1 inch.      







Upstream, the anomalous mid-level height departures initially featured over the 

West Coast at the start of week-2 are favored to shift eastward, where there 

are hints of trough development in the ensembles over the eastern Pacific and 

West Coast later in the period. This is expected to bring cooler conditions to 

an otherwise hot start of the period for parts of the Pacific Northwest and 

California (particularly in the northern portions of the Central California 

Valley). However, both the GEFS and ECMWF ensembles depict the maximum height 

center amplifying over the lower Four Corners and Southern Plains. Given the 

position and strength of the ridge axis in the latest ensemble guidance, 

above-normal temperatures are favored to return, and renew the risk for 

excessive heat across the south-central CONUS later in May. This is reflected 

in the PET guidance indicating increased chances (20-30%) for maximum daytime 

temperatures exceeding the 85th percentile and 100 degrees F along the Rio 

Grande during the middle of week-2 and  a slight risk for excessive heat is 

posted for the region. Similar heat signals are also evident further west 

across the Sonoran Desert of California and southern Arizona, though maximum 

temperatures are not expected to exceed hazard criteria over this part of the 

country for this time of year. The excessive heat potential will continue to be 

closely monitored over the Desert Southwest, lower Four Corners, and Southern 

Plains as these regions were consistently plagued with excessive heat 

conditions for much of the warm season last year.  With warmer and drier than 

normal conditions favored, a slight risk of high winds is also posted for parts 

of the Desert Southwest, Southern Rockies, and Southern Plains (May 17-21). 

This is supported in the GEFS and ECMWF ensembles depicting an anomalous 

surface high near the Front Range of Colorado and a deepening thermal low over 

the Desert SW to induce episodes of high winds and elevate the wildfire risk. 







No hazards are issued for Alaska. Snowmelt season is underway and frozen rivers 

are beginning to break up, leading to the potential for river flooding related 

to ice-jams. Currently, there are no indications of impending major river 

break-ups or serious threat of ice-jamming so no flooding-related hazards are 

posted at this time. Caution will continue to be exercised as river break-up 

can be unpredictable and local conditions can change quickly.



FORECASTER: Nick Novella 



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