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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1951Z Aug 10, 2022)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
351 PM EDT Wed Aug 10 2022

Valid 12Z Sat Aug 13 2022 - 12Z Wed Aug 17 2022

...Monsoonal moisture/rainfall threat continues for the Southwest
and Intermountain West/Rockies...

...Excessive heat threat across the Plains, with warming
temperatures in the Northwest next week...


...Overview...

A fairly stagnant trough-ridge-trough pattern is forecast this
weekend across the contiguous U.S.. Shortwaves will deepen and
then maintain a trough in the East, an upper low off the West
Coast lifts northeastward into British Columbia, and a warm upper
high meanders near the Central/Southern High Plains. Upper ridging
is also forecast to expand into the West by Tuesday-Wednesday of
next week, increasing temperatures to well above average,
particularly in the Northwest. The ridge aloft will also continue
to support monsoonal moisture streaming into the Southwest,
Intermountain West and Rockies through much of next week. A
lingering frontal boundary over Florida will provide a focus for
rainfall there, while possible shortwave energy rounding the ridge
could lead to rounds of showers/thunderstorms across the
Midwest/Upper Great Lakes this weekend, with rain chances
expanding south and east into early next week.


...Guidance Evaluation/Predictability Assessment...

The latest guidance is in good agreement on the broad synoptic
pattern of dipole troughs along the coasts and ridging across the
central-western part of the country during the medium range. The
00z EC/ECE had the least run-to-run/ensemble member spread with
respect to the eastern trough axis, in particular. On day 3 a
general model blend of the 00z EC/CMC/UK and 06z GFS were joined
by the 00z GFS to account for some discrepancies in the 00z EC and
06z GFS. The gmb was continued on day 4 with the exception of the
00z GFS. The 00z ECE and 06z GEFS were added to the blend on day 5
as they seemed to resolve the eastern U.S. trough reasonably well
compared to the deterministics. The 00z ECE was favored in the
blend on through day 7 as it carries little to no spread over the
lower 48 and displays the overall pattern comparitively to model
consensus.


...Weather/Hazards Highlights...

Parts of the West have seen persistent monsoonal moisture over the
past couple of months, and the rest of this week and into next
week will continue that pattern. In fact, notable moisture
anomalies are forecast to stream into parts of the Great Basin and
the Rockies and produce rain and thunderstorms. A Slight Risk of
Excessive Rainfall was introduced today for Saturday and Sunday
over portions of northwestern Arizona, including Mohave, Yavapai
and Coconino counties. Rain totals may increase by Monday-Tuesday
for the Northern/Central Rockies in particular. Meanwhile, a moist
airmass and a lingering frontal boundary will cause showers and
thunderstorms across the Florida Peninsula into early next week.
Farther north, shortwave impulses rounding the ridge could lead to
rain and storms across the Midwest/Upper Great Lakes into the Ohio
Valley this weekend, but with low confidence on the specifics.
Then rain chances could increase for the Ohio Valley to
Appalachians and the East Coast early next week along a cold
front, but the details remain uncertain there as well.

Very warm to hot temperatures around 10-15F above average, though
mainly not to record-breaking levels, are forecast across the
Northern and especially the Central Plains over the weekend, with
some gradual moderation and shift southward through the workweek,
though highs could still reach 100F in the Southern Plains. As the
upper ridge expands into the Northwest, this will warm up
temperatures there and cause highs 10-20F above normal by
Tuesday-Wednesday. Meanwhile, below normal highs are possible in
the east-central U.S. behind the cold front, with the most
persistent cooler than average weather in the Ohio and Tennessee
Valleys toward the Mid-Atlantic. Given the rainfall and cloudiness
over the Southwest and Great Basin into the Rockies, highs are
likely to be several degrees below normal there through much of
next week.

Kebede/Tate

Hazards:
- Heavy rain across portions of the Southwest, the Great Basin,
and the Central Rockies, Sat-Wed, Aug 13-Aug 17.
- Heavy rain across portions of the Central and Southern Rockies
and adjacent High Plains, Mon-Wed, Aug 15-Aug 17.
- Heavy rain across portions of Florida, Sat, Aug 13.
- Flooding occurring or imminent across portions of the Upper
Mississippi Valley.
- Excessive heat across portions of the Central Plains and Middle
Missouri Valley, Sat-Sun, Aug 13-Aug 14.
- Excessive heat across portions of the Central and Southern
Plains and Lower Mississippi Valley, Sun-Wed, Aug 14-Aug 17.
- Excessive heat across portions of Texas, Tue-Wed, Aug 16-Aug 17.
- Excessive heat across portions of the Pacific Northwest and
Northern Great Basin, Tue-Wed, Aug 16-Aug 17.

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