409
FXUS21 KWNC 191758
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT June 19 2024

SYNOPSIS: Early in week-2, mid-level low pressure is forecast to develop across
the West while mid-level high pressure restrengthens over the eastern and
central U.S. By the beginning of July, strong mid-level high pressure is
expected to expand westward to the West. The risk of excessive heat is likely
to remain elevated for many areas of the lower 48 states through the beginning
of July. Frequent periods of thunderstorms with locally heavy rainfall and an
increased risk of flash flooding are expected to persist for the upper
Mississippi Valley.

HAZARDS

Moderate risk of excessive heat for parts of the Mid-Atlantic and Southeast,
Thu-Fri, Jun 27-28.

Slight risk of excessive heat for parts of the eastern and central
U.S.,Thu-Wed, Jun 27-Jul 3.

Slight risk of excessive heat for parts of the central to southern Great
Plains, Southwest, and California, Mon-Wed, Jul 1-3.

Slight risk of heavy precipitation for the eastern Dakotas, northern Iowa, and
upper Mississippi Valley, Thu-Wed, Jun 27-Jul 3.

Flooding possible for the upper Mississippi Valley.

Rapid onset drought risk for the Mid-Atlantic, Carolinas, and eastern Corn
Belt.

DETAILED SUMMARY

FOR SATURDAY JUNE 22 - WEDNESDAY JUNE 26:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR THURSDAY JUNE 27 - WEDNESDAY JULY 03: An ongoing heat wave across the
Northeast and Mid-Atlantic is forecast to peak this weekend before temperatures
slightly cool early next week. However, by the start of week-2 (June 27),
southwesterly flow and a strengthening ridge aloft are expected to bring hotter
temperatures back, especially to the Mid-Atlantic and Southeast. Based largely
on the GEFS and ECMWF calibrated heat index tool, a moderate risk of excessive
heat is posted from the Carolinas north to Philadelphia. The ECMWF calibrated
heat index tool is the most bullish with the excessive heat signal and depicts
more than a 40 percent chance of heat index values exceeding the 90th
percentile and 105 degrees F within the designated moderate risk area. A slight
risk of excessive heat extends through the entirety of week-2 and includes
areas as far north as Boston, but the GEFS is cooler than the ECENS.



The anomalous ridge aloft, with 500-hPa heights increasing to near or more than
594 dam, and the GEFS/ECENS heat index tool support a slight risk of excessive
heat for much of the Southeast, Ohio Valley, Middle to Lower Mississippi
Valley, and humid areas of the Central to Southern Great Plains. This slight
risk of excessive heat is valid through July 3rd as model output features a
consistent signal throughout week-2, although there could be brief periods when
temperatures moderate. As the anomalous 500-hPa ridge expands westward later in
week-2, there is an increasing chance of excessive heat for parts of the
Southwest and Central Valley of California from July 1 to 3. The valid time and
spatial extent of this slight risk of excessive heat is supported by the
evolving 500-hPa height pattern along with the GEFS and ECENS Probabilistic
Extremes Tool (PET) where maximum temperatures have a 20 percent chance of
exceeding the 85th percentile and reaching heat advisory thresholds.



The National Hurricane Center (NHC) is monitoring two potential systems for
tropical cyclone (TC) development. The initial potential TC would track west
into northern Mexico in the next few days. The NHC states that there is a 30
percent chance for a second TC to form in the southwestern Gulf of Mexico
during the next week. Model solutions have trended towards a westward track
which would decrease the chances for heavy precipitation along the U.S. Gulf
Coast for week-2. Due to a lack of model support, the slight risk for heavy
precipitation along the Texas Gulf Coast is discontinued.



The GEFS and ECMWF ensemble means depict multiple shortwave 500-hPa troughs
progressing east from the western to the north-central CONUS overtop the
expanding mid-level ridge. This longwave pattern along with uncalibrated
24-hour precipitation amounts from the GEFS and ECENS support a slight risk of
heavy precipitation across the upper Mississippi Valley, northern Iowa, and
eastern Dakotas through the end of week-2. Thunderstorms could trigger flash
flooding. In addition, minor to moderate river flooding is expected to persist
into the beginning of July, especially across southern Minnesota.



Rapid Onset Drought (ROD) risk is posted for much of the Mid-Atlantic,
Carolinas, and eastern Corn Belt. These areas are most vulnerable to the rapid
onset of drought due to: 30-day precipitation deficits of 2 to 4 inches, low
soil moisture, and above-normal temperatures with high evapotranspiration rates
forecast during the next two weeks.

FORECASTER: Brad Pugh

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