008
FXUS21 KWNC 211905
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 21 2025

SYNOPSIS: Lingering mid-level high pressure over the Pacific Northwest brings
the potential for extreme heat to portions of the northwestern Contiguous U.S.
(CONUS) early in week-2. A frontal system is favored to move over the central
and eastern CONUS at the outset of the forecast period, resulting in
potentially heavy precipitation for portions of the Great Plains and
Mississippi Valley early in week-2. Disturbed weather and a possible surface
low pressure to form off the Carolina coast results in enhanced precipitation
and high winds, some of which may affect coastal portions of the Southeast U.S.

HAZARDS

Slight risk of extreme heat for portions northwestern CONUS west of the
Rockies, Fri-Sat, Aug 29-30.

Slight risk of heavy precipitation for portions of the Southern and Central
Plains, and the Lower and Middle Mississippi Valley, Fri-Sat, Aug 29-30.

Slight risk of heavy precipitation for portions of the Southeast U.S. and
Mid-Atlantic, Fri-Tue, Aug 29-Sep 2.

Slight risk of high winds for coastal areas from the Florida-Georgia border
north to and including the Delmarva Peninsula, Fri-Tue, Aug 29-2.

DETAILED SUMMARY

FOR SUNDAY AUGUST 24 - THURSDAY AUGUST 28:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY AUGUST 29 - THURSDAY SEPTEMBER 04: Model ensembles are in good
agreement regarding an amplified ridge at 500-hPa over western Canada and the
northwestern CONUS, along with a thermal low at the surface over interior
Washington state at the outset of week-2, resulting in above-normal
temperatures and the potential for extreme heat. While the timing of this surge
in temperatures is now mostly in week-1 and model solutions quickly deamplify
this ridge, there remains the potential for this heat event to linger into the
week-2 period. Raw probabilities from the GEFS and ECMWF indicate at least a
20% chance of maximum temperatures to exceed 95F for at least the first portion
of the forecast period. The GEFS is a little more bullish, indicating a chance
for 95F for most of week-2, while the ECMWF cools daytime temperatures off more
quickly. A slight risk for extreme heat remains posted for non-coastal portions
of the northwestern CONUS west of the Rockies for Aug 29-30, during which model
agreement is strongest.



Model ensembles also indicate a fairly strong mid-level trough over the
northeastern U.S. early in week-2, which model solutions also flatten out
quickly as the forecast period progresses. A frontal system associated with
this trough is favored to bring potentially heavy precipitation to the
midsection of the Lower 48. Like the heat for the Northwest, this enhanced
precipitation is most likely during the week-1 period but has the potential to
linger into the beginning of week-2. A slight risk of heavy precipitation is
posted  for portions of the Southern and Central Plains, and the Lower and
Middle Mississippi Valley for Aug 29-30, when probabilistic output from the
GEFS and ECMWF both indicate at least a 20% chance of daily precipitation
accumulations to exceed 0.5 inches. While the ECWMF favors enhanced
precipitation to continue well into week-2, there is insufficient evidence to
extend this hazard into September, but this situation will be closely monitored
in the coming days.



Lingering instability from the frontal system mentioned above along with
abundant tropical moisture leads to the potential for enhanced precipitation
and high winds along the southeastern U.S. coastline. Model solutions from the
ECMWF and GEFs both indicate the potential for a surface low to spin up off the
Carolina coast and possibly become a tropical cyclone (TC) during the week-2
period, and at the very minimum enhancing precipitation along the southeastern
coast. At this time a slight risk of heavy precipitation is posted for Aug
29-Sep 2 for portions of the Southeast U.S. and MId-Atlantic, and a slight risk
of high wind is posted for coastal areas from the Florida-Georgia border north
to Delaware Bay for the same days. Model agreement is unfortunately low
regarding the details of this potential tropical activity, precluding better
detail regarding time and regional effects, so this situation will be closely
monitored in the coming days.



Precipitation accumulations have been quite low over the last month over
portions of western Tennessee and northern Mississippi, an area highlighted for
the potential of rapid-onset drought (ROD) last week. While antecedent rain is
well below average, models indicate that the region is favored to receive
precipitation exceeding 1 inch during the week-2 period (at least 40%
probability), therefore the ROD hazard covering western Tennessee and northern
Mississippi has been removed.

FORECASTER: Danny Barandiaran

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