287
FXUS21 KWNC 131808
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 13 2025

SYNOPSIS: There are elevated chances for excessive heat continuing from week-1
over the Southern Plains associated with a strong area of mid-level high
pressure over the southern tier of the contiguous U.S. (CONUS), with this heat
risk potentially expanding westward over parts of the Central California Valley
and Desert Southwest towards the middle of week-2.  A potentially strong
surface low tracking into the Great Lakes may bring locally heavy precipitation
amounts to the northeastern CONUS along with episodes of high winds early in
the period.

HAZARDS

Moderate risk of excessive heat for portions of southern Texas, Wed-Thu, May
21-22.

Slight risk of excessive heat for portions of the Southern Plains and the Lower
Mississippi Valley, Wed-Sat, May 21-24.

Slight risk of excessive heat for parts of California and the Desert Southwest,
Thu-Sun, May 22-25.

Slight risk of high winds for parts of the Pacific Northwest and California,
Wed-Sun, May 21-25.

Slight risk of heavy precipitation for portions of the Great Lakes, Ohio
Valley, Mid-Atlantic, Appalachians, and the Northeast, Wed-Thu, May 21-22.

Slight risk of high winds for much of the eastern CONUS, Wed-Fri, May 21-23.

DETAILED SUMMARY

FOR FRIDAY MAY 16 - TUESDAY MAY 20:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY MAY 21 - TUESDAY MAY 27: Early next week, dynamical models are in
good agreement featuring shortwave troughing ejecting from the Rockies with a
widespread coverage of positive 500-hPa height departures downstream over the
eastern U.S., as well as across much of the southern tier of the CONUS. While
the subtropical ridging anomalies don`t appear especially pronounced, both the
GEFS and ECMWF maintain at least 591 dam heights in the ensemble mean extending
from southern Texas to southern Florida, translating to 1.5 to 2.5 standard
deviations above normal for this time of the year. These height departures in
normalized space at the lower latitudes are typically a good indicator for
excessive heat conditions at the surface where there is better support in the
tools for an elevated risk of heat continuing into the week-2 period.
Probabilistic Extremes Tools (PETs) from the GEFS and ECWMF indicate 30 to 50%
chances for maximum daytime temperatures exceeding the 90th percentile and 95
degrees F.  In consideration of the evolving height pattern, and the NWS Heat
Risk tool indicating extreme levels (red and purple values) of heat late over
southern Texas late in week-1, a moderate risk of excessive heat is added to
the outlook for May 21-22. A broader slight risk area remains posted for May
21-24. This area is expanded to include the Lower Mississippi Valley where the
National Blend of Models (NBM) guidance also depicts several locations
approaching near record breaking temperatures, as well as farther westward into
New Mexico with much of the anomalous subtropical ridging favored to retrograde
westward next week.



As the aforementioned troughing lifts out of the upper Midwest, there is better
model support for stronger mid-level ridging encroaching the West Coast from
the eastern Pacific to also bring an increased risk of early season heat for
parts of California and into the Desert Southwest. Relative to yesterday, there
is greater spatial coverage in the GEFS and ECMWF PETS for daytime temperatures
exceeding the 90th percentile, with increased chances (>20%) for maximum
temperatures over 95 degrees over the Central California Valley, and over 105
degrees F in parts of the Desert Southwest starting on day 9 (May 22). While
these temperatures would not meet hazard criteria during the peak of the
summer, such temperatures may reach advisory or warning levels based on NWS
Heat Risk climatology for this of the year, and a corresponding slight risk is
posted for May 22-25, before much of the ridging aloft is favored to ease. In
addition to the possible heat over the West Coast, enhanced offshore flow is
favored tied to a strong mean surface high in the eastern Pacific. While this
is likely to bring a period of suppressed precipitation, a strong mean surface
pressure gradient favored over northern California and the Pacific Northwest in
the GEFS and ECMWF ensembles is expected  to promote episodes of high winds.
This is reflected in the PETs indicating increased chances for wind speeds
exceeding the 85th percentile, and a slight risk of high winds is posted for
May 21-25.  It is worth noting that any elevated wind speeds further across the
Southern Plains and Desert Southeast may elevate the risk for wildfire
conditions given the strong signals for above-normal springtime temperatures.



Across the Midwest, there is also good model support for a deeper surface low
tracking into the Great Lakes by the outset of week-2 compared to previous
guidance. Based on uncalibrated tools, the highest precipitation amounts are
favored over parts of the Ohio Valley, Great Lakes, Mid-Atlantic and the
Northeast, with the GEFS being the weakest with these totals compared to the
ECMWF and Canadian. PETs are relatively modest in terms of the 3-day
precipitation totals exceeding an inch, but do maintain increased chances for
3-day amounts exceeding the 85th percentile over the northeastern CONUS. Given
this, and model trends favoring a deeper surface low and stronger shortwave
troughing aloft in the latest ensemble runs, a slight risk of heavy
precipitation is posted for May 21-22. Consequently, a slight risk of high
winds is also posted for much of the eastern CONUS where there is support in
the PETs for wind speeds exceeding the 85th percentile tied to the surface low.




No hazards are issued over Alaska. Cooler than normal springtime temperatures
are favored mainly north of the Brooks Range, with a slight tilt towards
above-normal precipitation for much of the Mainland and Southeast, but nothing
approaching hazard thresholds.

FORECASTER: Nick Novella

$$