375
FXUS02 KWBC 251242
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
842 AM EDT Tue Jun 25 2024

Valid 12Z Fri Jun 28 2024 - 12Z Tue Jul 02 2024

...Hazardous heat threats to focus across parts of the South next
weekend and into early next week...


...Overview...

An upper ridge centered over the South will expand and strengthen
with time during the period, with its core most likely settling
over the Lower Mississippi Valley this weekend and into early next
week. This ridge will bring an increased threat for hazardous heat
to portions of the Southern U.S. for much of the period. To the
north, a series of shortwaves/troughs will progress from West to
East across the northern tier into early next week. Showers and
thunderstorms will accompany the associated frontal boundaries,
with the best chance for heavy to excessive rainfall across parts
of the Midwest on Friday. Heavy rainfall threats may increase again
for parts of the northern Plains to Upper Midwest early next week
as the next shortwave reaches the region.


...Guidance/Predictability Assessment...

Overall the latest dynamical and machine learning guidance offers
better than average agreement and continuity through the period.
There are some lingering differences in the timing and strength of
the progressive northern stream shortwaves which would have impacts
on sensible weather and QPF, and even these details could take
until the short range period to fully resolve. Given the agreement,
a general model blend (with the ensemble means, especially later
in the period) should suffice as a good starting point for the
forecast.


...Weather/Hazards Highlights...

A frontal system through the northern tier should focus the best
heavy to excessive rainfall potential centered over an area
including parts of Illinois/Wisconsin/Iowa/Missouri -- overlapping
with areas which have seen significant rainfall recently. Showers
and thunderstorms accompanying this system should reach into the
eastern U.S. and back into the central Plains next weekend.

Coverage of storms across the Southwest should decrease by Friday
but, rainfall coverage may increase once again especially in New
Mexico and the Southern Rockies over the weekend and early next
week with a renewed threat for heavy rainfall and flash flooding,
particularly over Burn Scars/Slot Canyons.

Showers and thunderstorms associated with frontal boundaries may
also linger across the Southeast/Florida through the period, but
dry conditions/high FFGs should limit and flash flood threats.
Another northern tier system may generate an episode of potentially
heavy rainfall over parts of the Northern Plains and Upper Midwest
around next Monday into Tuesday. This system will require close
monitoring given the region`s sensitivity to additional rainfall.

Hazardous heat potential will focus across the South from the
southern Plains into the Southeast much of the period underneath
the building and nearly stagnant upper ridge. This will bring
several days of above normal temperatures (both daytime highs and
overnight lows) from the south-central Plains eastward. A fairly
broad area may challenge record warm lows, especially during the
weekend. Meanwhile the main area of cooler temperatures will be
across the northern tier, where upper shortwaves and surface fronts
provide some relief to normal summertime heat.

Santorelli/Rausch


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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