Prognostic Meteorological Discussion
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FXUS21 KWNC 131856
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT June 13 2024

SYNOPSIS: A heat wave is forecast to be ongoing across portions of the Midwest,
Mid-Atlantic, and Northeast as well as much of the Interior West at the outset
of week-2 associated with broad mid-level high pressure over the central and
eastern contiguous U.S.(CONUS). By the middle of the period, this feature is
forecast to begin shifting westward, potentially bringing some relief from the
heat for the East Coast by the end of week-2. Enhanced southerly flow and an
influx of tropical moisture favor elevated chances of heavy precipitation and
potential flooding near the Gulf of Mexico coast, although there is uncertainty
regarding timing and coverage of the heaviest precipitation.

HAZARDS

Moderate risk of excessive heat across portions of the Midwest, Fri-Mon, Jun
21-24.

Moderate risk of excessive heat across portions of the Northeast and
Mid-Atlantic, Fri, Jun 21.

Slight risk of excessive heat across portions of the central and eastern CONUS,
Fri-Wed, Jun 21-26.

Slight risk of excessive heat across portions of the Interior West and
California, Fri-Wed, Jun 21-26.

Moderate risk of heavy precipitation along the western and central Gulf of
Mexico coast, Fri-Sun, Jun 21-23.

Slight risk of heavy precipitation for much of the Gulf Coast and Lower
Mississippi Valley, Fri-Tue, Jun 21-25.

Slight risk of heavy precipitation across portions of the Northern Plains and
Upper Mississippi Valley, Fri-Mon, Jun 21-24.

Slight risk of high winds across portions of the eastern Rockies, and the
Central and Southern Plains, Fri-Tue, Jun 21-25.

Flooding possible across portions of the Gulf of Mexico coast.

Rapid Onset Drought Risk for parts of the eastern Corn Belt and Mid-Atlantic.

DETAILED SUMMARY

FOR SUNDAY JUNE 16 - THURSDAY JUNE 20:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY JUNE 21 - THURSDAY JUNE 27: Todays ensemble solutions from the GEFS
and ECMWF are showing good continuity with yesterday particularly with regard
to the mid-level ridge centered over the eastern CONUS at the outset of week-2.
The ECMWF is especially bullish, with a 594dm maximum on day 8 over the Central
Plains, setting the stage for continued chances for excessive heat to affect
much of the CONUS during the forecast period. Guidance from the GEFS and ECMWF
Probabilistic Extremes Tools (PETs) continue to depict at least a 40%
probability of daily maximum temperatures exceeding the 85th percentile for
portions of the Northeast, Mid-Atlantic, and Midwest on Jun 21. The predicted
ridge quickly flattens, dropping heights over the East Coast, subsequently also
lowering probabilities of excessive heat; however the 40% threshold continues
to be met over the Midwest through the 24th. Therefore, a moderate risk for
excessive heat is posted for portions of the Mid-Atlantic and Northeast for Jun
21, and for portions of the Midwest for Jun 21-24. At this point the GEFS and
ECMWF solutions diverge, with the GEFS favoring cooler conditions while the
ECMWF maintains the heat over the East. The GEFS solution is preferred due to
historical skill in the region with respect to summertime excessive heat. Both
the GEFS and ECWMF PETs continue to indicate at least a 20% probability of
daily maximum temperatures exceeding the 85th percentile for a broader area of
the central and eastern CONUS for Jun 21-26, encompassing much of the Tennessee
Valley and Michigan, as well as greater coverage for the Mid-Atlantic and
Northeast relative to the moderate risk described above. Much of the Interior
West is also influenced by this broad ridge, which is also indicated by the
PETs with both the GEFS and ECMWF indicating widespread 20% chances for maximum
temperatures to exceed the 85th percentile for most of the forecast period.
Therefore, a slight risk for excessive heat is posted for Jun 21-26 for much of
the Interior West, as well as the southern Central Valley.



In addition to the widespread potential for excessive heat for large portions
of the CONUS, ensemble solutions continue to depict an increase in tropical
moisture and convective activity over the southern Gulf of Mexico late in
week-1 and continuing into week-2. Todays solutions distribute the heaviest
precipitation more widely relative to yesterday, and continue to favor
potentially heavy precipitation for much of the Gulf Coast. The GEFS and ECMWF
PETs depict at least a 20% probability of 3-day precipitation totals to exceed
the 85th percentile and at least one inch for much of the Gulf Coast for Jun
21-25, with higher probabilities and the potential for exceeding 2 inches early
in the forecast period. Therefore a moderate risk for heavy precipitation is
posted for portions of the western and central Gulf Coast for Jun 21-23, and a
slight risk for heavy precipitation extending further inland and including the
rest of the Gulf Coast for Jun 21-25. Finally, abundant antecedent rainfall
over much of eastern Texas has resulted in most of the area reservoirs at or
near capacity. Given the potential for heavy rainfall during week-2, a risk for
possible flooding is also highlighted for portions of eastern Texas and
southern Louisiana.



The weak trough over the West Coast mentioned earlier is also favored to
introduce some instability downstream over the Northern Tier, which paired with
passing shortwave disturbances provide the potential for periods of heavy
precipitation for portions of the Upper Midwest throughout week-2 and
particularly through the middle of the period. This is well-indicated by the
ECMWF (and to a lesser extent the GEFS) PETs, which depict at least a 20%
probability of 3-day precipitation totals to exceed the 85th percentile and 1
inch for Jun 21-24. Therefore a slight risk for heavy precipitation is posted
for portions of the Upper Midwest and Upper Mississippi Valley for dates
indicated above. The synoptic pattern also favors enhanced winds along the
eastern Rockies and western Great Plains. The ECMWF and GEFS both indicate high
probabilities (>60%) of wind speeds to reach at least 10kt, and the ECMWF
wind-gust forecast depicts a near-certainty for gusts exceeding 20kt, also for
the early and middle portions of the forecast period. Therefore a slight risk
for high winds is posted for portions of the eastern Rockies and western Plains
for Jun 21-25.



Portions of the Mid-Atlantic from northern Virginia to southern New Jersey, the
Ohio Valley and Midwest have had substantial precipitation deficits over the
last month. With soil moisture deficits already in place, an extended heat wave
for the region predicted, and minimal precipitation anticipated through at
least the middle of week-2, these areas are highlighted in todays outlook for
the potential of rapid onset drought.

FORECASTER: Danny Barandiaran

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