Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Fri Jul 30 2021
Valid 12Z Mon Aug 02 2021 - 12Z Fri Aug 06 2021
...Lingering monsoonal moisture and heavier rain for parts of the
Interior West Monday..
...Heavy rainfall threat for parts of the South/Southeast and
perhaps Mid-Atlantic...
...Overview...
Positive height anomalies over western/central Canada and
southwest of California will favor continued troughing in the
eastern states next week. This will promote cooler than normal
temperatures east of the Plains with highest rainfall chances
along and ahead of a slowly southward-moving cold front into the
Southeast. The Interior West will see diminishing rainfall,
focused along the Rockies and perhaps shifting to the Plains later
next week.
...Guidance/Predictability Evaluation...
Through the 12Z/18Z guidance, the models and ensembles remained in
good agreement overall with the pattern evolution through about
midweek. Recent deterministic runs have wavered on how quickly (or
slowly) to bring in height falls the Pac NW late in the week (or
beyond) and at what pace to erode troughing settling into the Ohio
Valley. Multi-day ensemble trends favor a slower trend in the East
to raise heights but a split trend in the Pac NW between the ECMWF
ensembles (slower to bring in height falls) vs the GEFS ensembles
(quicker). Favored the ECMWF ensembles by next Thu/Fri with
support from the Canadian and some GFS runs as well as the lack of
a clear upstream kicker over Alaska.
...Weather Highlights/Hazards...
With the upper high around the lower CO River Monday, mid-level
energy will spur afternoon convection over the northern/central
Rockies, some of which may contain heavier rain. As heights build
a bit over the Southwest, the moisture source will decrease and
rain coverage/intensity will decrease through the week. In the
East/Southeast, troughing will push a cold front close to or into
the Gulf by midweek. Abundant moisture ahead of the boundary will
support heavier rain chances anywhere from Texas eastward to the
Carolinas. As the upper pattern remains mostly in place, the front
may wobble about due, in part, to areas of low pressure that may
act to enhance rainfall into the Mid-Atlantic.
Temperatures will slowly moderate from below normal in much of the
Interior West (owing to clouds and rainfall) early in the week to
near or slightly above normal by the end of next week. Areas along
the Canadian border may see the warmest anomalies of +5 to +10
from eastern Montana to the western Great Lakes. Much of the
East/Southeast will see near to below normal temperatures along
and behind the cold front, perhaps as much as 10 degrees below
normal for early August on some days.
Fracasso
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, 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