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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1858Z Jul 13, 2024)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 PM EDT Sat Jul 13 2024

Valid 12Z Tue Jul 16 2024 - 12Z Sat Jul 20 2024

...Hazardous Heat for parts of the Central to Eastern U.S. for
early-mid next week. High heat to build over the West next week...


...Overview...

Heat focusing upper level ridging will persist through early-mid
next week over the southern half of the nation to bring widespread
above normal to hazardous temperatures. Upper trough development
over the eastern/northeastern Pacific into later next week will act
to build upper ridging over western North America and upper trough
amplification over the east-central continent. Energy digging to
the lee of the western ridge will increasingly work down into
downstream southern tier upper ridging as a heatwave moderating
cold front sinks down across much of the central and eastern U.S..

Meanwhile, upper level shortwaves will work over the Midwest/Great
Lakes and Northeast/Mid-Atlantic. Temperature moderating fronts
will sink south across the central U.S. and the East, with
potential to sink down into the South/Southeast later week.
Rain/thunderstorm chances will increase by these fronts. Daily
rain/convection chances will linger near the Four Corners region
and south-central High Plains as fueled by monsoonal moisture.

...Guidance/Predictability Assessment...

The 12Z model guidance suite maintains better than average
agreement on the synoptic scale across the continental U.S. through
the end of the week. By Saturday, the GFS becomes a little stronger
with the trough over the central U.S., but good placement overall.
It is also not quite as strong with the western U.S. upper ridge
when compared with the model consensus. There are also some modest
differences across New England with upstream trough passages from
Quebec. A general deterministic model blend sufficed as a good
starting point in the forecast process through Thursday, followed
by 30-40% of the ensemble means by Friday/Saturday.

...Weather/Hazards Highlights...

Monsoonal moisture will linger 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 planned
for Day 4 (Tuesday) and Day 5 (Wednesday) for the southern
Rockies and into eastern Colorado in a region with protracted
favorable upper diffluence.

Favorable upper level support and well defined/wavy surface fronts
set to shift southward across much of the central and eastern U.S.
will lead to multiple rounds of showers and thunderstorms. With
ample moisture and instability in place, locally heavy rainfall
will be possible and may lead to instances of flash flooding. A WPC
Day 4 (Tuesday) Marginal Risk ERO is set across the Ohio/Mid-
Mississippi Valleys/central Plains, and a Slight Risk area is
planned from central Indiana to central Ohio, where the strongest
model signal exists along with wet antecedent conditions and
anomalous PWs. The Day 5 (Wednesday) ERO extends from the Mid-
South to the Mid- Atlantic as the main front shifts southeastward.
Precipitation chances will progress farther southward across much
of the rest of the central and eastern U.S. mid-next week as this
cold front moves south, and daily precipitation chances will
persist in Florida with summertime convection from sea breeze
convergence. Locally heavy rain will be possible in these areas
with heavy thunderstorm activity.

Much of the nation will experience above average temperatures next
week and a threat for widespread record values while 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 Midwest/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 tick upward
again in a pattern with increasing hot conditions over the West.

Hamrick/Schichtel


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