223
FXUS02 KWBC 300656
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Sun Jun 30 2024

Valid 12Z Wed Jul 3 2024 - 12Z Sun Jul 7 2024


...Major heatwave expected for the lower elevations of California
and the Desert Southwest next week, and remaining hot and humid for
the south-central states...

...Pattern Overview...

Multiple shortwave passages across the northern tier of the nation
will fuel scattered to numerous showers and storms for the middle
to end of the week, particularly across the Midwest and portions
of the Central Plains where the heaviest rainfall is likely. Heat
and humidity will continue to make weather headlines across much of
the southern tier states as a strong ridge of high pressure aloft
governs the overall weather pattern, and heat also expands across
much of California and the lower elevations of Arizona and southern
Nevada as the upper ridge builds across the West by the end of the
forecast period. There will also be copious moisture in place
across much of the Southern Rockies through mid-week that will
fuel scattered storms, followed by drier weather.

...Guidance/Predictability Assessment...

The 00Z models are in very good agreement for the beginning of the
forecast period Wednesday, with just some minor mesoscale
differences with the shortwaves crossing southern Canada.
Therefore, a general model compromise works as a starting point in
the forecast process. The same thinking holds true going into the
4th of July Holiday, even though the GEFS mean is a little more
suppressed with the West Coast upper ridge. Similar to the past
couple of days, the greatest model differences going into the end
of the week are centered across the Western U.S., and with the
northward extent of the upper ridge, and also with a trough
dropping south near the Northern Rockies. Model spread is less for
the eastern half of the U.S., and the use of the ensemble means
accounted for about half of the forecast blend by next Sunday.

...Weather/Hazards Highlights...

There will likely be a few mesoscale convective complexes that
cross the Central Plains and Midwest on Wednesday in conjunction
with a quasi-stationary frontal boundary. Deep moisture advecting
northward from the western Gulf will intercept this boundary and
fuel the development of showers and strong thunderstorms, some of
which could train over the same general areas and lead to some
instances of flooding. With the potential for some 1-2 inch per
hour rainfall rates, a Slight Risk area remains valid going into
the new Day 4 ERO Wednesday across portions of eastern Kansas and
into central Missouri. The overall QPF signal in the guidance for
the Day 5 period on the 4th is looking more diffuse with scattered
higher QPF maxima, so a broad Marginal Risk area is planned from
northern Oklahoma to the Ohio Valley, with potential Slight Risk
areas in future updates as the details become more evident. There
is also another Marginal Risk area planned for the Upper Midwest
where a separate round of convection is possible.

Monsoonal flow into the Southwest states will likely continue the
threat for showers and storms going into Wednesday. There is a Marginal
risk in place across parts of Arizona and New Mexico for the Day 4
ERO, with saturated soils in many of these areas owing to heavier
rainfall in the short range forecast period. The good news is the
deeper moisture should be south of the Mexico border for the 4th of
July, and therefore no Marginal Risk area is planned for the new
Day 5 outlook.

It will continue to remain hot and humid across the Southern U.S.
for the middle of the week and into next weekend, with the hottest
conditions centered across the Southern Plains where triple digit
high temperatures are likely. Some of this heat likely reaches the
Mid-Atlantic region after a brief cool-down by the end of the week
with highs returning to the 90s amid increasing humidity levels.
There will likely be some abatement to the heat going into next
weekend, but still feeling summer-like. It will also be getting
very hot for the inland lower elevations of California and into the
Arizona Deserts with widespread 105-115 degree readings likely,
and locally higher for the normally warmer locations.

Hamrick


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






















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