433
FXUS21 KWNC 061809
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 06 2026

SYNOPSIS: Amplified mid-level high pressure drifting into the Four Corners
Region brings the risk of extreme heat to much of the western, central, and
southeastern Contiguous U.S. (CONUS) through most of week-2. This pattern is
expected to enhance the monsoonal circulation, potentially bringing tropical
moisture and a risk of heavy precipitation into parts of the southwestern CONUS.

HAZARDS

Moderate risk of extreme heat for much of the Great Basin, Desert Southwest,
California Central Valley, Great Plains, Mississippi Valley, Gulf Coast,
Georgia, and the Carolinas, Tue-Fri, Jul 14-17.

Slight risk of extreme heat for much of the western and central CONUS as well
as the Gulf Coast, Southeast, Tennessee Valley, and the southern Mid-Atlantic,
Tue-Sun, Jul 14-19.

Slight risk of heavy precipitation for the Southern Rockies and portions of the
Desert Southwest, Tue-Fri, Jul 14-17.

DETAILED SUMMARY

FOR THURSDAY JULY 09 - MONDAY JULY 13:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY JULY 14 - MONDAY JULY 20: Multiple model ensembles depict anomalous
mid-level ridging building into the Four Corners Region early in week-2, with
500-hPa heights reaching a maximum of 596-dm during the early and middle part
of the period, after which slight deamplification is possible. Meanwhile, a
mid-level trough with near normal 500-hPa heights is forecast to settle into
the northeastern CONUS. This pattern favors above-normal temperatures across
most of the CONUS, and since the timing is near the height of summer, a
widespread risk of extreme heat is posted across a large part of the CONUS.
Only parts of the Far West, central and eastern Great Lakes, Northeast, and
northern Mid-Atlantic are excluded, consistent with ensemble model means and
internal heat index guidance. Southerly flow from the Gulf of America and the
upper tropics is expected to prevail across the central and eastern CONUS,
increasing dewpoints that would exacerbate conditions by pushing heat index
values to hazardous levels.



The uncalibrated extreme heat tool shows much of the CONUS with 50% or greater
chances of either maximum temperature or heat index to exceed the 90th
percentile at some point during week-2, as well as heat wave onset near the
beginning of week-2 and lasting at least 3 to 5 days. A moderate risk of
extreme heat is posted where ensemble means, dynamical models, and internal
heat risk guidance show the best chances for hazardous temperatures and/or heat
index values, specifically the California Valleys, lower elevations of the
interior West, the Plains, the Mississippi Valley, the Gulf Coast, and portions
of the South Atlantic States for Jul 14-17. A slight risk of extreme heat is
also posted for an area extending farther north and east into the western Great
Lakes, parts of the Tennessee and Ohio Valleys, and most of the South Atlantic
States until late week-2 (Jul 19). Toward the end of the period, the European
ensemble (ECENS) mean and GEFS mean show a slow deamplification of the strong
mid-level ridge, reducing the extreme heat threat, but it should be noted that
the typical increase in model spread at later forecast time frames may be at
least partially responsible for the deamplification trend in the ensemble means.



Intense heat over the Southwest is likely to induce a thermal surface thermal
low pressure which should pull tropical moisture northward into the region,
kicking off the Southwest monsoon season. Dynamical models depict the potential
initiation of monsoon convection as week-2 gets underway. The Probabilistic
Extremes Tools (PETs) from the ECENS, GEFS, and Canadian ensembles (CMCE) are a
little more robust and consistent with this development today, with 20 to 40
percent chances for rainfall above the 85th climatological percentile and
exceeding one-half inch shown for much of the region during the first half of
week-2. A slight risk of heavy precipitation is posted for much of the
Southwest, consistent with the guidance. The signal is somewhat weaker over the
last half of week-2, at least partly in concert with the possible slow
deamplification of the strong mid-level ridge. In addition to the heavy rain
threat, monsoonal thunderstorms can also produce dry lightning, resulting in
increased wildfire risk.

FORECASTER: Rich Tinker

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