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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2024Z Aug 11, 2022)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Thu Aug 11 2022

Valid 12Z Sun Aug 14 2022 - 12Z Thu Aug 18 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...

The medium range period will begin Sunday with a continued
trough-ridge-trough pattern across the lower 48. As next week
progresses, there should be a trend toward the upper high/ridge
expanding into the West, leading to well above average
temperatures in the Northwest. The ridge aloft with embedded
shortwave energy will also continue to support monsoonal moisture
streaming into the Southwest, Intermountain West, and Rockies
through the week, with rain eventually spreading into portions of
the Plains and Mississippi Valley. Meanwhile the trough across the
East may deepen and close off an upper low around midweek, which
could cause multiple days of rainfall in the Northeast, but
dependent on the position of the upper low and the associated
surface low/fronts, which remain uncertain at this point.


...Guidance Evaluation/Predictability Assessment...

There was a bit more uncertainty with the synoptic pattern
compared to yesterday, particularly with respect to the eastern
U.S. trough. The trough-ridge-trough pattern was captured well by
the latest guidance, though. A general model blend of the 00z
EC/UK/CMC and 06z GFS was utilized on days 3 and 4 with the 00z EC
being favored through day 5 due to a more consistent signal and
reasonable approach to the southern ridge and eastern trough.
Models, including the latest 13z NBM, have trended dryer since
overnight with respect to the qpf produced by the eastern trough
over parts of the coastal Northeast on days 4-6. The 00z ECE/CMCE
were incorporated into the gmb on day 5 to smooth out small scale
discrepancies found in the western ridge axis. The ensembles were
favored through the rest of the period.


...Weather/Hazards Highlights...

Parts of the West have seen persistent monsoonal moisture over the
past couple of months, and next week will continue that pattern as
anomalously high moisture streams into the Southwest, Great Basin,
and Rockies in conjunction with small-scale shortwave energy to
produce rain and thunderstorms, particularly in the afternoon and
evening hours. Slight Risks of excessive rainfall are in place for
portions of the Desert Southwest on Sunday and the Central Rockies
on Monday, where current forecasts show the best chances for heavy
rainfall. Heavy rain amounts look to continue through midweek in
the Central Rockies. There are increasing chances for rainfall to
spread into parts of the Central/Southern Plains and Mississippi
Valley as the week progresses. Elsewhere, the Gulf Coast and into
Florida could see scattered storms with a moist airmass and a
couple of frontal boundaries. Then as a surface low is currently
forecast to track across the Ohio Valley through the Mid-Atlantic
toward the Northeast, rain is forecast for those areas. There's
increasing confidence in a multi-day rain event occurring for much
of the coastal Northeast, from New Jersey up to Maine through
mid-week.

Very warm to hot temperatures around 10-15F above average, though
mainly not to record-breaking levels, are forecast across the
Central Plains Sunday into Monday, with a gradually moderating
trend Tuesday onward yielding below normal highs. As the upper
ridge expands into the Northwest, this will warm up temperatures
there and cause highs 10-20F above normal for Tuesday-Thursday.
Meanwhile, below normal highs are expected 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 Central and Northern Rockies,
Sun-Tue, Aug 14-Aug 16.
- Heavy rain across portions of the Southwest and the Great Basin,
Sun-Thu, Aug 14-Aug 18.
- Heavy rain across portions of the Central and Southern Rockies
and High Plains, Mon-Thu, Aug 15-Aug 18.
- Heavy rain across portions of the Mid-Atlantic and New England,
Mon-Tue, Aug 15-Aug 16.
- Heavy rain across portions of New England, Tue-Wed, Aug 16-Aug
17.
- Flooding occurring or imminent across portions of the Upper
Mississippi Valley.
- Excessive heat across portions of the Central Plains and the
Middle Missouri Valley, Sun, 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-Thu, Aug 16-Aug 18.
- Excessive heat across portions of the Pacific Northwest and
Northern Great Basin, Tue-Thu, Aug 16-Aug 18.

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