763
FXUS21 KWNC 241757
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 24 2024

SYNOPSIS: Early in week-2, a weak low pressure system and trailing cold front
are forecast to progress eastward across the Great Plains and Mississippi
Valley. A broad area of mid-level high pressure is forecast to strengthen over
the south-central contiguous U.S. (CONUS) at the beginning of June and then
expand northward. This would favor above-normal temperatures for much of the
lower 48 states with a chance of excessive heat for the Rio Grande Valley
during week-2. A deep mid-level low and enhanced onshore flow favors
above-normal precipitation across Alaska.

HAZARDS

Slight risk for excessive heat across portions of the Rio Grande Valley and the
Southern Plains, Sat-Fri, Jun 1-7.

Slight risk for excessive heat across portions of the Florida Peninsula,
Sat-Mon, Jun 1-3.

Slight risk for heavy precipitation across portions of the Central and Southern
Plains, and Middle and Lower Mississippi Valley, Sat-Mon, Jun 1-3.

Slight risk for high winds for areas downslope of the Northern and Central
Rocky Mountains, Sat-Sun, Jun 1-2.

Rapid onset drought risk across parts of southern Texas.



DETAILED SUMMARY

FOR MONDAY MAY 27 - FRIDAY MAY 31:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY JUNE 01 - FRIDAY JUNE 07: The GEFS and ECMWF ensemble means depict
a shortwave 500-hPa trough progressing east from the western to the
north-central CONUS by the beginning of week-2. Their daily forecasts also
feature a low pressure system tracking east from the Canadian Prairies to
Manitoba with a trailing cold front. This predicted 500-hpa/surface pattern is
expected to result in thunderstorms with locally heavy rainfall across parts of
the Great Plains and Mississippi Valley. The highest risk for heavy
precipitation has shifted south relative to yesterday and is in northeastern
Texas, eastern Oklahoma and Kansas, and western Missouri and Arkansas. The
slight risk of heavy precipitation (Jun 1-3) is consistent with the
uncalibrated ECMWF ensemble mean probabilities for more than 1 inch and the
Probabilistic Extremes Tools (PET). Since parts of this region have saturated
soils from recent heavy rainfall, locally heavy rainfall may trigger flash
flooding.



The shortwave trough and surface low pressure along the Canadian border at the
onset of week-2 may increase chances for high winds along the downslope of the
Northern and Central Rockies. There are some signals among some of the ensemble
members of the GEFS and ECENS for strong winds downslope of the Rocky Mountains
consistent with a chinook wind event. Therefore, a slight risk of high winds is
posted for downslope regions of the Northern and Central Rockies.



In South Florida, there is generally continued uncertainty in the strength of
the above-normal temperatures in the area. The anomalous ridge that has been
focused over the region in recent days leading to heat advisory conditions
doesnt appear to be as robust. However, the GEFS and ECENS PETs continue to
indicate chances for temperatures to exceed the 85th percentile. And a
skill-weighted GEFS/ECENS tool indicates a 20 to 40% chance of apparent
temperatures exceeding the 105 deg F. Therefore, a slight risk of excessive
heat remains forecast for Jun 1-3 across southern Florida.



Following predicted heat relief for Texas during the early to middle part of
next week, the ECMWF ensemble mean is bullish on a strengthening subtropical
ridge over northern Mexico and the south-central CONUS during the first week of
June. A slight risk of excessive heat is designated to areas closer to the Rio
Grande Valley. Supported by the GEFS and ECENS PETs forecast at least a 20%
chance of actual temperatures to exceed the 85th climatological percentile and
100 deg F through much of week-2. A skill weighted bias-corrected apparent
temperature tool indicates at least 20% chances for apparent temperatures to
exceed 110 deg F. Therefore, a slight risk of excessive heat is posted for all
of week-2, Jun 1-7, for parts of the Rio Grande Valley. Further north, chances
for excessive heat have diminished significantly relative to yesterday and the
slight risk across central Texas has been discontinued.



The greatest risk for rapid onset drought (ROD) during the remainder of May
into early June exists for southern Texas. The ROD hazard is based on 30 to
60-day precipitation deficits, low soil moisture, and likelihood of
above-normal temperatures along with the lack of a strong wet signal during the
next two weeks.



Multi-model ensemble means are in excellent agreement that a deep 500-hPa
closed low develops over the Aleutians and southwestern Alaska by the beginning
of June. This anomalous mid-level trough is likely to enhance onshore flow to
southern Alaska where above-normal precipitation is favored. Since the GEFS and
ECMWF PETs depict probabilities of less than 20 percent for 3-day precipitation
amounts exceeding 2 inches, a heavy precipitation hazard is not posted.

FORECASTER: Ryan Bolt

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