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Extended Forecast Discussion
 
(Latest Discussion - Issued 2041Z Jul 04, 2022)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
440 PM EDT Mon Jul 04 2022

Valid 12Z Thu Jul 07 2022 - 12Z Mon Jul 11 2022

...Prolonged Heatwave This Week and Upcoming Weekend Across
Southern Plains to Mid South...

...Overview...

A persistent and strong upper level high centered over the
southern U.S. through this week and into the upcoming weekend will
keep very hot temperatures in place across much of the central
CONUS. Combined with the humidity, heat indices are likely to
exceed 105-110F in places and with very little nighttime relief in
temperatures, a prolonged heatwave is expected. The multiple days
of high heat with little nighttime temperature relief will
increase the potential impacts to sensitive and more vulnerable
groups. Elsewhere across the CONUS, around the periphery of this
upper ridge, troughing is expected in the northwest and northeast
U.S., with periodic rounds of showers and thunderstorms likely
moving through the flow. This could produce multiple episodes of
stronger storms with the potential of locally heavy rainfall
across the Ohio Valley to Mid-Atlantic and Southeast late this
week and this weekend.

...Guidance Evaluation/Predictability Assessment...

The latest deterministic and ensemble guidance remains in good
agreement for the large scale setup and evolution from later this
week through early next week across the CONUS. The upper ridge
strengthens/builds and reasserts itself over the Southern Plains
while troughing initially over the Pacific Northwest eventually
works its way to dig a stronger trough over the Great Lakes and
Northeast by this weekend. The embedded shortwaves and mesoscale
details are yet to be resolved but there is growing consensus for
a strong frontal passage and shortwave trough across the Ohio
Valley and Mid-Atlantic Friday into Saturday. Some of the large
model differences were with the approach and passage of shortwave
energy into the Pacific Northwest Friday into Friday night. Here,
the GFS was a faster outlier compared to the rest of the guidance.
For the forecast blend, the days 3-5 were composed of the latest
deterministic guidance while for days 6-7, higher weights of the
GEFS and ECENS means were used for the typical model spread and
uncertainty. 

...Sensible Weather and Hazards...

Scattered showers and storms are likely across much of the U.S.
from the Rockies eastward at times this week into early next week,
with enhanced totals in the vicinity of a couple of frontal
boundaries stretching generally west to east across the northern
half of the country. Northwesterly flow aloft and abundant
moisture and instability will create a favorable pattern for
mesoscale convective systems and high rainfall rates within a
broad area from the northern Plains/Midwest/Upper Great Lakes into
the Ohio Valley and Appalachians to the East Coast. Areas of
excessive rainfall/flash flooding are possible through the
weekend, but considerable uncertainty with the placement of heavy
rain amounts precludes delineating Slight Risk areas in the
experimental day 4-5 Excessive Rainfall Outlook at this point.
Scattered thunderstorms are also likely in the Southeast through
the week, and the current forecast shows the eastern part of the
main front sinking southward from meandering over the Mid-Atlantic
into the Carolinas and eventually the Gulf Coast by next weekend,
leading to more focused rainfall in the Southeast and clearing for
the Northeast behind the front. At the same time a frontal system
emerging into the northern Plains next weekend may provide added
convective focus over that region once again. Meanwhile monsoonal
moisture could persist through much of the week with moist
southwesterly flow/embedded shortwaves leading to mainly diurnally
driven showers and storms over the Four Corners states. The
southern Plains and California into the Great Basin should be the
most consistently dry areas during the period.

Very hot weather is expected to persist across the southern half
of the Plains/Mississippi Valley underneath the strong upper
ridge/high. High temperatures near or exceeding 100F are expected,
which is between 5 and 15 degrees above normal. Combined with the
humidity, daily maximum heat indices 105-110F+ are likely at times
across a large portion of the Mid-Mississippi Valley southward
into the southern Plains and Gulf Coast/Southeast. The repeating
days of high heat/humidity and lack of any appreciable nighttime
relief (lows upper 70s to low 80s for some areas) will increase
the potential impacts from this prolonged heatwave to the more
sensitive and vulnerable populations. Meanwhile, the West Coast
could see cooler than normal conditions late week before
moderating closer to average, while the Desert Southwest should
see near normal temperatures becoming a few degrees above average.
Parts of the East may see slightly below normal temperatures
spreading south this weekend into Monday behind a cold front.


Tate/Taylor


Hazards:
- Heavy rain across portions of the Midwest, Ohio Valley, and into
the interior northern Mid-Atlantic, Thu-Fri, Jul 7-Jul 8.
- Heavy rain across portions of the Mid-Atlantic, Thu-Sun, Jul
7-Jul 10.
- Heavy rain across portions of the eastern Gulf Coast to the
Southeast, into the Mid-Atlantic and southern Appalachians,
Sat-Sun, Jul 9-Jul 10.
- Flooding possible across portions of the upper Mississippi
Valley into the northern Plains.
- Flooding occurring or imminent across portions of northeastern
South Dakota and northern Minnesota.
- Excessive heat across portions of the southern Plains into the
lower Mississippi Valley, Thu-Mon, Jul 7-Jul 11.
- Excessive heat across portions of the central/southern Plains,
the lower to mid-Mississippi Valley, and interior Deep South,
Thu-Sun, Jul 7-Jul 10.
- Excessive heat across portions of the central Plains, the
mid-Mississippi Valley, and into the Ohio and Tennessee Valleys,
Thu-Fri, Jul 7-Jul 8.

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, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are
at:

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