664
FXUS21 KWNC 091821
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 09 2026

SYNOPSIS: Highly amplified mid-level high pressure is forecast to peak in
amplitude across the north-central contiguous U.S. (CONUS) during week-1.
Dynamical model ensembles have trended more east with this feature, and now
support increasing extreme heat risks from the Northern Plains to the Midwest
and Eastern Seaboard at the outset of week-2 coinciding with the peak of summer
time heating. There is a bit less confidence across the West compared to
previous outlooks, where above-normal temperatures are likely, but the
decreasing amplitude of mid-level high pressure reduces the chances of extreme
heat. This pattern is also expected to enhance the monsoonal circulation,
potentially bringing tropical moisture and a risk of heavy precipitation into
parts of the southwestern CONUS.

HAZARDS

High risk of extreme heat across portions of the Northern Plains and Upper
Mississippi Valley, Fri, Jul 17.

Moderate risk of extreme heat across the Northern and Central Plains, Upper and
Middle Mississippi Valley, lower Great Lakes, and the Tennessee and Ohio
Valleys, Fri-Sat, Jul 17-18.

Moderate risk of extreme heat across portions of the southern Mid-Atlantic and
Southeast, Fri-Sat, Jul 17-18.

Slight risk of extreme heat for most areas from the Great Plains to the East
Coast, Fri-Mon, Jul 17-20.

Slight risk of extreme heat across much of the western CONUS, Fri-Thu, Jul
17-23.

Slight risk of heavy precipitation across portions of the Central and Southern
Rockies and Desert Southwest, Fri-Tue, Jul 17-21.

Rapid Onset Drought risk across the Northern Plains.

DETAILED SUMMARY

FOR SUNDAY JULY 12 - THURSDAY JULY 16:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY JULY 17 - THURSDAY JULY 23: A broad mid-level ridge is forecast
across most of the CONUS at the outset of week-2, with the ECMWF ensemble
depicting a 595-dm 500-hPa center across the Lower Mississippi and Tennessee
Valleys. As a result, +60 meter positive height anomalies extend across the
Midwest and Ohio Valley, with +30 meter positive height anomalies reaching the
East Coast on day-8 (Jul 17). While the ECMWF has always been on the eastern
edge of the guidance in terms of ridge placement, this is a substantial shift
compared to yesterday, and the GEFS has also trended in this direction.
Additionally, both the deterministic 0z GFS and ECMWF depict the most amplified
ridging over the eastern U.S. early in week-2. The forecast leans more on the
ECMWF due to recent model skill in persisting the previous heat wave across the
eastern U.S., and therefore, risks of extreme heat are now being highlighted
from the Northern Plains eastward across the Ohio Valley and to the East Coast.



A high risk for extreme heat remains posted for Jul 17 across the Northern
Plains and adjacent areas of the Upper Mississippi Valley where skill weighted
heat risk guidance indicates probabilities greater than 50 percent for heat
index values to exceed 100 deg F tied to higher than normal humidity forecast
over the region. These northern areas have lower thresholds for extreme heat
compared to farther south, justifying the high risk. The moderate risk for
extreme heat is expanded across the Midwest and Ohio Valley, valid Jul 17-18,
and consistent with 40 percent or greater probabilities of maximum temperatures
exceeding the 85th climatological percentile in the ECMWF Probabilistic
Extremes Tool (PET). The 0z ECMWF ensemble continues to depict maximum
temperatures in the upper 80s to low 90s deg F, and with a notable upward trend
in temperatures compared to yesterday in the GEFS. Higher heat index values are
likely farther south, potentially exceeding 105 deg F across the Middle
Mississippi Valley. Hot temperatures and predicted dry conditions also support
an enhanced risk of Rapid Onset Drought across portions of the Northern Plains.



There are also stronger signals for extreme heat across the Eastern Seaboard,
with a moderate risk for extreme heat across the southern Mid-Atlantic into the
Southeast, Jul 17-18. This is mainly tied to elevated probabilities for heat
index values to exceed the 90th climatological percentile in the GEFS/ECMWF
skill weighted heat risk guidance, and also supported by enhanced subtropical
ridging and above-normal sea surface temperatures over the northeastern Gulf of
America. The uncalibrated 0z ECMWF supports a farther northward expansion of
the moderate risk through the northern Mid-Atlantic where there are emerging
chances of temperatures exceeding 100 deg F. However, there is still some
uncertainty tied to the amplitude of troughing over Atlantic Canada, with the
GEFS favoring lower mid-level heights compared to the ECMWF. A broad slight
risk for extreme heat covers most areas from the Great Plains to the East
Coast, Jul 17-20, with enough support, especially in the ECMWF, to justify
expanding the slight risk for extreme heat through southern New England, with
the greatest potential being earlier in the period. The National Blend of
Models (NBM) indicates the potential for both record high maximum and high
minimum temperatures across parts of the eastern Coastal Plain, suggesting
little overnight relief from the heat.



Elevated chances of extreme heat are also forecast across much of the western
CONUS, although there is also uncertainty as the GEFS is quicker to shift the
ridge west, and both the GEFS and ECMWF begin to weaken the ridge amplitude by
the middle of the period. There is a decent signal in the uncalibrated 0z GEFS
and ECMWF ensembles for temperatures above 100 deg F across low elevation areas
of the Great Basin and Rockies, and possibly above 105 deg F across the
California Central Valley supporting a slight risk for extreme heat for all of
week-2. Probabilities in the PETs are on the lower side and no longer support a
moderate risk.



High temperatures over the Southwest are likely to induce thermal surface low
pressure which combined with the ridge axis becoming positioned near the Four
Corners, should pull tropical moisture northward into the region, kicking off
the Southwest monsoon season. The ECMWF PET depicts 40-60 percent chances for
rainfall exceeding the 85th climatological percentile and one-half inch early
in the period, decreasing later in week-2. Probabilities in the GEFS PET are
generally low, but still indicate an enhanced signal (at least 20 percent
chance) through the middle of the period. Therefore, a slight risk of heavy
precipitation is posted for much of the Central and Southern Rockies and Desert
Southwest, Jul 17-21, consistent with the PETs, and the uncalibrated ECMWF and
GEFS which depict enhanced precipitation extending northward into Utah and
Colorado. The signal is somewhat weaker toward the end of week-2, tied to slow
weakening of the mid-level ridge. In addition to the heavy rain threat,
monsoonal thunderstorms can also produce dry lightning, resulting in increased
wildfire risk.

FORECASTER: Thomas Collow

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