130
FXUS21 KWNC 281919
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 28 2024

SYNOPSIS: Early in week-2, surface high pressure is forecast off the Southeast
coast, with southerly return flow of very warm, humid air expected over the
Central and Eastern contiguous U.S. (CONUS). A weak low pressure system and its
trailing cold front moving across this portion of the nation are likely to
trigger showers and thunderstorms, with the heaviest activity expected across
the Northeast. A broad area of mid-level high pressure is forecast over the
south-central states before expanding northwestward and strengthening across
most of the interior West. This would lead to the first significant heat wave
of the season for much of the Interior West, which has experienced a relatively
cool spring up to now. A deep mid-level low and enhanced onshore flow favors
above-normal precipitation across Southeast Alaska.

HAZARDS

Moderate risk for excessive heat over for the Central Valley of California,
Thu-Mon, Jun 6-10.

Slight risk for excessive heat across much of the Interior West, Wed-Tue, Jun
5-11.

Slight risk for excessive heat across portions of the Rio Grande Valley and
adjacent parts of Texas, Wed-Tue, Jun 5-11.

Slight risk for excessive heat across portions of the Florida Peninsula,
Wed-Sat, Jun 5-8.

Slight risk for heavy precipitation over the Northeast, Wed-Sat, Jun 5-8.

Slight risk for high winds for downwind areas of the Northern Rocky Mountains,
Wed-Tue, Jun 5-6.

Rapid onset drought risk across parts of southern Texas.

DETAILED SUMMARY

FOR FRIDAY MAY 31 - TUESDAY JUNE 04:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY JUNE 05 - TUESDAY JUNE 11: The GEFS, ECMWF ensemble mean (ECENS)
and the Canadian ensemble mean (CMCE) continue to depict a strong subtropical
ridge over northern Mexico and into southern Texas during the week-2 period. In
the vicinity of the Rio Grande Valley, 500-hPa heights are predicted to range
between 588-593 dm, with height departures ranging between zero and +60 meters.
Though the most intense heat associated with this ridge is expected south of
the U.S.-Mexican border, maximum temperatures of 100-105 deg F are anticipated
across the vicinity of the Rio Grande Valley during this period, with heat
index values approaching or slightly exceeding 110 deg F. However, the National
Blend of Models (NBM) does not depict any near or record high temperatures
across the Rio Grande Valley early in week-2. It does show a number of high
nighttime minimum temperature records expected to be tied or broken, with lows
only dropping to near or slightly above 80 deg F.  The GEFS and ECENS
Probabilistic Extremes Tools (PETs) forecast at least a 20% chance of actual
temperatures to exceed the 85th climatological percentile and 100 deg F, with a
possible slight weakening of the heat signal during the middle of week-2. A
slight risk of excessive heat is posted for all of week-2, Jun 5-11, for middle
and lower portions of the Rio Grande Valley.



In central and southern Florida, the GEFS and ECENS PETs continue to indicate
at least a 20% chance for temperatures to exceed the 85th percentile. A
skill-weighted, bias-corrected GEFS/ECENS hybrid tool indicates a 20 to 40%
chance of apparent temperatures exceeding 105 deg F. Therefore, a slight risk
of excessive heat remains forecast across inland areas of the southern half of
the Florida peninsula.



Across the Interior West during week-2, the predicted amplification and
expansion of mid-level ridging and positive height anomalies favor the first
major heat wave of the season. This heat will contrast strongly against the
background of a relatively cool spring up to this point. Ensemble means from
the various models predict positive height anomalies of at least 120-180 meters
above normal over most of the Interior West, excluding the southern
Intermountain region. The Snake River Valley in southern Idaho and portions of
eastern Oregon and eastern Washington may top out at or slightly above 90 deg
F. However, overnight lows forecast near 60 deg F will provide adequate relief
from the daytime heat. A slight risk for excessive heat is indicated over much
of the Interior West for the duration of week-2. Elsewhere, even warmer
temperatures are expected for the Central Valley of California, under the
strengthening mid-level ridge. A moderate risk of excessive heat is posted for
this area from Jun 6-10, with forecast daytime highs ranging from the mid 90s
to low 100s and maximum heat index values around 105 deg F. It is not clear as
to whether this heat wave will continue through week-2, or possibly begin to
wane by the very end of the period.



As for precipitation, the uncalibrated ECMWF and various PET guidance depict
the best chance for 3-day precipitation amounts to exceed 1-inch, and where
there is at least a 20% chance of the 85th historical percentile being
exceeded, is over the Northeast, Jun 5-8.  This is associated with the expected
approach and passage of a low pressure system and trailing cold front moving
through the region. Showers and thunderstorms are also forecast to continue
west-southwestward from there across the Tennessee Valley and south-central
Plains near where the front is expected to stall. However, there is not quite
enough support between the various ensemble means to include this on the map
today.  Tropical moisture streaming northeastward from the central Caribbean
Sea is forecast to pass south and east of Florida during week-2, influencing
primarily Cuba and the Bahamas.



There is a slight risk of high winds (20-25 mph) over areas downwind of the
Northern Rockies, Jun 5-6, reasonably well supported by the various PET wind
tools, especially the ECENS and the CMCE. This is associated with increased
west-southwest flow aloft, and with weak lee cyclogenesis anticipated in this
area.



The greatest risk for rapid onset drought (ROD) during early to mid 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 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 1.5 inches
precluding the posting of a heavy precipitation hazard.

FORECASTER: Anthony Artusa

$$