856
FXUS21 KWNC 301948
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 30 2024

SYNOPSIS: Strong and persistent mid-level high pressure has the potential to
bring an extended period of excessive heat to many areas from the High Plains
to the Pacific Coast. A slight risk of excessive heat covers this large area
for the entirety of week-2, with a moderate risk posted for much of the
interior West, also for the entire period. A high risk of excessive heat is
limited to the first day of the period in the central California Valley. Toward
the end of week-2, the slight excessive heat risk expands across southern
Texas. Meanwhile, episodes of high winds from the southern High Plains through
portions of the Rockies and Desert Southwest, along with dry and unusually hot
conditions, may promote the rapid development and spread of wildfires. To the
east, an excessive heat risk extends through all of week-2 across most of
Florida and adjacent areas, with the greatest potential in portions of the
interior Florida Peninsula.

HAZARDS

High risk for excessive heat for the Central Valley of California, Fri, Jun 7.

Moderate risk for excessive heat for the Central Valley of California and
adjacent lower foothills, Fri-Sat, Jun 7-8.

Moderate risk for excessive heat for much of the interior West, Fri-Thu, Jun
7-13.

Moderate risk for excessive heat over part of the interior Florida Peninsula,
Fri-Thu, Jun 7-13.

Slight risk for excessive heat in most areas from the High Plains to the
Pacific Coast, Fri-Thu, Jun 7-13.

Slight risk for excessive heat in much of coastal California and part of
southwestern Arizona, Fri-Mon, Jun 7-10.

Slight risk for excessive heat in southern Texas, Tue-Thu, Jun 11-13.

Slight risk for heavy precipitation in part of the Northeast, Fri, Jun 7.

Slight risk for episodes of high winds across much of the Texas Big Bend, Four
Corners states, Great Basin, and Desert Southwest, Fri-Thu, Jun 7-13.

Rapid onset drought risk across parts of southern Texas.

Rapid onset drought risk in part of the central Florida Peninsula.

DETAILED SUMMARY

FOR SUNDAY JUNE 02 - THURSDAY JUNE 06:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY JUNE 07 - THURSDAY JUNE 13: The GEFS, ECMWF ensemble mean (ECENS)
and the Canadian ensemble mean (CMCE) all show a moderate to strong mid-level
ridge over the western contiguous states (CONUS) as week-2 begins, with the
greatest 500-hPa heights (>590 dm) over the Four Corners region, and the
largest 500-hPa height anomalies centered near the northern Great Basin. The
CMCE solution features a stronger mid-level ridge than yesterday, more like the
ECENS, which changed little. Both show positive 500-hPa height anomalies >+18
dm at the start of week-2. The GEFS mean is also fairly amplified (+12 to +18
dm), but is weaker than the other two ensemble means. Given the shift in the
CMCE today, the stronger mid-level ridge is the favored solution. This feature
is expected to weaken only slightly and drift slowly northward or northwestward
through the period, which keeps mid-level ridging over most of the West during
all of week-2. This set-up is favorable for the development and persistence of
excessive heat in a large part of the CONUS from the High Plains to the Pacific
Coast, potentially bringingmuch of this broad area its first heat wave of 2024.
Very warm to excessively hot air would already be in place as the period
begins, and the uncalibrated National Blend of Models (NBM) shows high chances
for temperatures to approach 105 deg. F in the central California Valley on the
first day of week-2. Somewhat lower 500-hPa heights may impinge on California
and some adjacent areas for the rest of the period, quickly reducing the high
excessive heat risk there, and eventually ending the slight excessive heat risk
along most of the California coast and part of southwestern Arizona around the
middle of week-2. The GEFS, CMCE, and ECENS all show cooler air slowly becoming
entrenched in this area as the period progresses. As the largest 500-hPa height
anomalies drift northward thereafter, the greatest excessive heat risks follow
suit. A broad area across the interior West, especially the lower elevations,
have the best chances to record exceptionally high temperatures, and a moderate
risk for excessive heat is posted here. With the expected persistence of the
mid-level ridge, the moderate risk has been extended through all of week-2.
There is more uncertainty in higher elevations and in areas farther to the
east, somewhat removed from the greatest 500-hPa height anomalies, so a slight
risk of excessive heat is posted across this large area, covering almost the
entire western half of the CONUS, for the entirety of the period. The ECENS and
CMCE uncalibrated output shows chances occasionally approaching 50 percent for
temperatures to reach 100 deg. F as far north as the Snake and Columbia River
Valleys, and adjacent lower elevations. In addition, most models (particularly
the ECENS) show abnormally high humidity entrenched across the West during
week-2, which could generate higher heat indices than usual given the same
temperatures.



Farther east, a frontal boundary is expected to pass through south Texas before
the week-2 period, leaving near normal temperatures across the region as the
period gets underway. This should keep excessive heat at bay until the last few
days of week-2, when increasingly hot air is expected to move back into the
region, creating a slight risk of excessive heat there late in the week. There
is a risk for rapid onset drought (ROD) during early to mid June for southern
Texas. The ROD hazard is based on 30 to 60-day precipitation deficits, low soil
moisture, and likelihood of periods of above-normal temperatures along with the
lack of a strong wet signal.



The GEFS and ECENS PETs continue to indicate a 20 to 40 percent chance for
temperatures to exceed the 85th percentile each day during the period. This
signal extends farther north than yesterday, spreading a slight risk of
excessive heat into portions of Georgia and South Carolina as well.. Abnormally
high 850-hPa temperatures are forced into the region on the backside of a
mid-level ridge, and persist through the forecast period. The ECENS shows daily
high temperatures hitting at least 90 deg. F every day at most sites, with
temperatures remaining 1.5 to nearly 4 deg. F above normal through almost the
entire period. A few inland areas could reach 95 to 100 deg. F on a few days,
with the best odds shown by the GEFS members. The climatologically-high
humidity will exacerbate the effects of the heat, generating heat indices well
into the 100s. Heat and humidity has the best chance of bringing excessive
heat to the interior central Florida Peninsula, where a moderate risk of
excessive heat has been posted for the entirety of week-2. Guidance shows
slightly cooler weather across south Florida, where a moderate excessive heat
risk was posted yesterday. Outside the central Florida Peninsula, where there
is a little more uncertainty, a slight risk of excessive heat is posted for the
entire period. In addition, the heat may combine with subnormal precipitation
over the next few weeks to promote rapid drought development across part of the
central Florida Peninsula.



As for precipitation, the uncalibrated ECMWF and PET guidance is somewhat drier
than yesterday, but enough members in the ECENS, GEFS, and CMCE show a frontal
complex dropping moderate to heavy rainfall as it moves through early week-2 to
maintain a slight risk of heavy precipitation over part of the Northeast for
the first day of week-2. Guidance is in good agreement that this system will
move faster than expected yesterday, exiting the northeastern CONUS quickly
after week-2 gets underway.



Multi-model ensemble means are in very good agreement that a deep 500-hPa
closed low will be located over the Gulf of Alaska by the start of week-2. This
anomalous mid-level trough is likely to enhance onshore flow to Southeast
Alaska where above-normal precipitation is favored. The GEFS, ECENS, and CMCE
PETs depict probabilities of about 20 percent for exceeding the 85th historical
percentile, but actual 3-day precipitation amounts remain below 2 inches
precluding the posting of a heavy precipitation hazard.

FORECASTER: Rich Tinker

$$