Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Aug 09 2022

Valid 12Z Fri Aug 12 2022 - 12Z Tue Aug 16 2022

...Monsoonal moisture/rainfall threat continues for the Southwest
and Intermountain West/Rockies this week, with some localized
heavy rain possible for the Gulf Coast states as well...

...Excessive heat threat from the interior Northwest to the
north-central Plains...


...Overview...

A fairly stagnant trough-ridge-trough pattern is forecast later
this week into early next week across the contiguous U.S., as
shortwaves deepen and then maintain a trough in the East, an upper
low off the West Coast lifts northeastward into British Columbia,
and an upper high meanders near the central/southern High Plains.
A cold front or two approaching the Gulf Coast and stalling will
provide a focus for moisture and rain/thunderstorms there and
lingering across much of Florida into early next week. Meanwhile,
persistent monsoonal moisture looks to continue across the
Southwest and expanding into the Intermountain West and Rockies
this week into next week.


...Guidance Evaluation/Predictability Assessment...

Broad consensus for amplified patterns over the East and West
coasts with an central U.S. ridge wane toward the end of the
period. A general model blend of deterministic guidance was
utilized through day 4 with an ensemble introduction by day 5 and
continuing through day 7. On day 3, the 00z EC/CMC/UK and 06z GFS
were used as they agreed on the overall trough-ridge-trough
pattern across the lower 48. We continued this blend into day 4
with some 00z GFS included to account for timing and intensity
spread in the upper trough over the Pacific Northwest/British
Columbia. The 00z ECE and 06z GEFS were incorporated into the
general model blend on day 5 to account for uncertainty associated
with an embedded shortwave propagating through southern Canada and
the Northern Plains. Day 6 was heavily weighted toward the 00z
EC/ECE due to reasonable and run-to-run consitency of the upper
trough over the East Coast and the central U.S. ridge with which
the 06z GFS/GEFS were a bit more inconsistent. The 00z CMC was a
bit too intense with respect to an upper vort over southern
Wyoming. The 06z GFS/GEFS and 00z CMCE were also incorporated into
the blend, albeit with lower weighting. Day 7 was a blend of the
ensembles with a bit of 00z EC included. The main area of
uncertainty on day 7 is in the deterministic 06z GFS, which has an
anomalous closed low centrered over the Upper Great Lakes/Michigan.


...Weather/Hazards Highlights...

Moisture streaming ahead of a couple of cold fronts moving into
the Southeast and toward the Gulf Coast late this week will
produce rain and thunderstorms in those areas. This could cause
localized flooding issues since storms should be slow-moving and
may train over the same areas. Rain chances are likely to continue
across much of Florida into early next week as the front stalls.
Farther north, the cold front should clear out most rainfall from
the Mid-Atlantic and likely the Northeast as well, but dependent
on how close to the New England coast a low along the cold front
sits. Shortwave impulses rounding the ridge could lead to rain and
storms across the Midwest/Upper Great Lakes into the Ohio Valley
this weekend into early next week, but with low confidence on the
specifics. Meanwhile, monsoonal moisture continues to impact the
Southwest into parts of the Great Basin and into the Rockies with
rainfall through the medium range period. Some locally heavy
totals are possible and a Slight Risk of flash flooding has been
added to the experimental Day 4 ERO.

Very warm to hot temperatures around 10-15F above average, though
not quite to record-breaking levels, are forecast across interior
portions of the Northwest and into the Northern/Central Plains
through the latter part of the week, and lasting across the
Central Plains and parts of the Mid-Mississippi Valley this
weekend into early next week. A slight southern shift is expected
with time, leading to highs nearing/reaching 100F forecast early
next week in the central/southern Plains. Farther east, 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. The Mid-Atlantic and Northeast should
experience clear and comfortable temeratures this weekend. Given
the rainfall and cloudiness over the Southwest and Great Basin,
highs are likely to be several degrees below normal there through
early next week.

Kebede/Tate


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