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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1856Z Jul 11, 2024)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Thu Jul 11 2024

Valid 12Z Sun Jul 14 2024 - 12Z Thu Jul 18 2024

...Hazardous to dangerous heat likely for parts of the Central to
Eastern U.S. next week...


...Overview...

Persistent upper level ridging will be in place next week across
the interior West, Southeast, and south-central U.S. and will
bring above normal to hazardous temperatures to much of the
nation. The ridge across the West will gradually weaken into early
next week, but may build again by later in the period. Meanwhile,
a series of potent upper level shortwaves will swing across the
Upper Midwest, Great Lakes, and Northeast, and a couple of frontal
boundaries will sink south across the north- central U.S. and the
Northeast. Precipitation chances will increase along these frontal
boundaries, and daily precipitation chances will also exist in the
Four Corners region as monsoonal moisture focuses over the area.


...Guidance/Predictability Assessment...

Model guidance remains in good agreement on the overall pattern,
with typical spread/uncertainty in the details. The most impactful
uncertainty will likely surround the timing of northern stream
shortwaves, which will affect the timing and location of fronts and
sensible weather at the surface. There is uncertainty that
increases later in the period with amplified troughing off the West
Coast and any energy into the Pacific Northwest ahead of it too.

Given pretty good overall agreement, the WPC forecast model blend
was comprised of a general deterministic blend of the
GFS/ECMWF/CMC/UKMET, with slightly more weight placed on the
GFS/ECMWF, for the first half of the period. Ensemble means from
the GEFS/ECENS were added to the blend for the second half of the
period to smooth out some differences.


...Weather/Hazards Highlights...

Monsoonal moisture will focus over portions of the Four Corners
region, which will allow for daily rounds of precipitation that
could result in flash flooding, especially near steep terrain and
burn scars. A Marginal Risk of Excessive Rainfall remains in place
for much of the region on Day 4 (Sunday) and Day 5 (Monday) for
much of the Four Corners region and portions of the southern
Rockies as moisture pushes north.

Across the Great Lakes and Northeast, upper level shortwaves and
surface fronts will provide support for multiple rounds of showers
and thunderstorms. With ample moisture and instability in place
across these regions, locally heavy rainfall will be possible and
may lead to isolated instances of flash flooding. A Marginal Risk
of Excessive Rainfall remains in place for much of the Great Lakes
region on Day 4 (Sunday), and the eastern Great Lakes and
Northeast on Day 5 (Monday), especially given the heightened
sensitivity in the Northeast following heavy rains this week. The
Storm Prediction Center also highlights parts of this region for
severe weather potential as well.

Elsewhere, precipitation chances will progress south across the
rest of the central and eastern U.S. mid-next week as a cold front
moves south, and daily precipitation chances will persist in
Florida with summertime convection. Locally heavy rain will be
possible in these areas with any heavier thunderstorm activity. The
West Coast and much of the Pacific Northwest will remain dry
through next week.

Much of the nation will experience above average temperatures
next week, becoming dangerously hot for many from especially the
central to eastern U.S.. Hazardous heat should slowly suppress
south and eastward with time as amplified troughing dips into the
Great Lakes and Northeast/Mid-Atlantic. Temperatures in the 110s
are likely to continue across the Desert Southwest, and highs near
or above 100 will be common in the central/southern Plains.
Temperatures across the Northwest may be marginally above normal
through early next week, but as upper ridging builds back in,
anomalies may tick upward again.


Santorelli/Dolan


Additional 3-7 Day Hazard information can be found on the WPC
medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw