683
FXUS21 KWNC 221759
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 22 2025

SYNOPSIS: Mid-level high pressure is forecast to strengthen over the West
leading to anomalous warmth to end May and start June. Extreme heat is most
likely to affect the Central Valley of California on May 30 and 31. A
stationary front is expected to be the focus for locally heavy rainfall from
the Central to Southern High Plains southeastward to the western Gulf Coast
through early week-2. During the first week of June, there is an increasing
risk of heavy rainfall across Florida and the northern Gulf Coast.

HAZARDS

Slight risk of extreme heat for the Central Valley of California, Fri-Sat, May
30-31.

Slight risk of heavy precipitation for parts of the Central to Southern Great
Plains, western Gulf Coast, and Lower Mississippi Valley, Fri-Sun, May 30-June
1.

Slight risk of heavy precipitation for parts of the Southeast, Mon-Thu, June
2-5.

DETAILED SUMMARY

FOR SUNDAY MAY 25 - THURSDAY MAY 29:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY MAY 30 - THURSDAY JUNE 05: Downstream of a deep 500-hPa trough over
Alaska, the ensemble mean solutions continue to depict a building mid-level
ridge over the western contiguous U.S. (CONUS) during the final week of May.
However, for the third consecutive day, models differ on the strength of this
ridge with the ECENS remaining the most amplified. By the beginning of week-2
(May 30), the ECENS features 500-hPa height anomalies of more than +120 meters
over northern California and the upper Great Basin with the GEFS and CMCE
having those anomalies ranging from +60 to +120 meters. These ensemble means
remain consistent indicating this mid-level ridge peaking in strength on May 30
and 31 before the ridge flattens with a transition to low-amplitude flow
throughout the lower 48 states. According to the NWS HeatRisk tool, extreme
heat thresholds are roughly maximum temperatures of 100 and 95 degrees F for
the Central Valley of California and the Great Basin, respectively. The ECENS
has maximum temperatures of near or more than 100 degrees F across the Central
Valley on May 30 and 31 with its probabilistic extremes tool (PET) having a 20
to 40 percent chance of maximum temperatures exceeding 100 degrees F. Since the
GEFS and CMCE have a weaker 500-hPa ridge, their PETs have less than a 20
percent chance of maximum temperatures reaching 100 degrees F for interior
areas of California. Despite the lack of support from the GEFS and CMCE, a
slight risk of extreme heat (May 30-31) remains posted for the Central Valley
of California due to good continuity from the ECENS. The combination of high
temperatures, low relative humidity, and drying vegetation may result in
elevated wildfire risk for that part of California. Although above-normal
temperatures are likely for much of the Great Basin and Southwest during
week-2, maximum temperatures are expected to remain below extreme heat
thresholds.



From May 30 to June 1, a stationary front is forecast to extend from the
Central and Southern High Plains southeastward to the western Gulf Coast and
Lower Mississippi Valley. This front is expected to be a focus for convection
with locally heavy rainfall. The slight risk of heavy precipitation has been
expanded northwest in todays outlook, to the Front Range of Colorado and
northeastern New Mexico as upslope flow could promote diurnal thunderstorms. As
of 5am EDT on May 22, the NHC states that there is a 50 percent chance of
tropical cyclone (TC) development across the East Pacific during the next seven
days. If this TC forms and tracks more northward, then enhanced mid-level
moisture may shift northward into the south-central CONUS which was another
factor supporting at least a slight risk of heavy precipitation for this
region. Locally heavy rainfall could trigger flash flooding or renewed river
flooding especially for northeastern Texas and western Louisiana, but
uncertainty regarding where the heaviest rainfall may occur during early week-2
precludes designating a flooding shape on the map but will continue to be
monitored.



Multi-model ensemble means continue to depict a surge of tropical moisture
spreading northward from the western Caribbean to Florida and the northern Gulf
Coast during the first week of June. Beginning from June 1-3 and continuing
through June 3-5, the GEFS and ECENS PETs shows a 20 to 40 percent chance of
3-day precipitation amounts exceeding the 85th percentile across Florida, the
northern Gulf Coast, and Coastal Plain of the Southeast which support a slight
risk of heavy precipitation. Based on 24-hour precipitation amounts from the
uncalibrated ensemble means, the heavy precipitation hazard is anticipated to
begin on June 2. According to the U.S. Drought Monitor, severe to extreme
drought covers south Florida including the Everglades. The wetter pattern
forecast to start June would be welcome drought relief for these areas.



The GEFS, ECENS, and CMCE depict a highly amplified 500-hPa trough over Alaska
through early week-2 which favors below-normal temperatures and above-normal
precipitation. Although the GEFS and ECENS PETs indicate a 20 to 40 percent
chance of 3-day precipitation amounts exceeding the 85th percentile across
southeastern Alaska through June 3, totals are not anticipated to reach
hazardous criteria.

FORECASTER: Brad Pugh

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