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Extended Forecast Discussion
 
(Latest Discussion - Issued 0648Z Aug 14, 2020)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 AM EDT Fri Aug 14 2020

Valid 12Z Mon Aug 17 2020 - 12Z Fri Aug 21 2020

...Dangerous heat for much of the West early next week...


...Overview...

A strong upper high will meander near the Desert Southwest next
week while troughing will retrograde slightly in the East. Well
above normal temperatures will approach and exceed records for
many locations from Idaho southward through the Colorado River
Valley. Rainfall will be focused over the Southeast around a
stalled front with lighter amounts over parts of the Rockies and
Upper Midwest.


...Guidance/Predictability Assessment...

With good ensemble agreement overall, the deterministic models
showed acceptable clustering so that a blended approach was used
as a starting point to the forecast. Uncertainty increased atop
the upper high with incoming Pacific shortwaves and how they
flatten the top side of the ridge over the Northwest and southern
Canada. In the East, lead troughing will exit northeastward but be
reinforced by the end of the week, tugging the axis westward.  GFS
runs may have been on the more aggressive side overall so the
ECMWF was weighted a bit more than the GFS. The UKMET/Canadian
offered some detail to the forecast though each was less
consistently clustered near the ensembles means.


...Weather/Hazard Highlights...

Upper high will promote record heat for many areas west of the
Rockies while some showers/storms may fire on the east side of the
Rockies over Colorado and New Mexico with limited moisture. Record
high max and min temperatures will persist over the Desert
Southwest and surrounding areas through the Great Basin and inland
areas of California through at least the first half of the week,
perhaps cooling a bit by next Thu/Fri. Temperatures in the 100s
will be common with highest readings over 120F in Death Valley.
Little to no rainfall is expected under the upper high.

With troughing over the East, showers/storms will be favored over
the Southeast westward to Texas especially in the afternoon. This
may drift northward into the Mid-Atlantic midweek as the front
wanders along the coast. Northern stream troughing will bring in
cooler than normal temperatures to portions of the Plains and
mid-Mississippi Valley through the week with the best rainfall
chances over the Upper Midwest.


Fracasso


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml