Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Tue Oct 05 2021
Valid 12Z Fri Oct 08 2021 - 12Z Tue Oct 12 2021
...Pattern Overview and Weather/Hazards Highlights...
A pesky upper low/trough will diminish over the east-central U.S.
Fri into the weekend along with a widespread wet pattern wrapping
from the Southeast and Mid-Atlantic back to the Great Lakes. The
south-central Appalachians may offer the most runoff risk as
enhanced by terrain and duration. Meanwhile, a split stream upper
trough and lead frontal system working from the West to the
north-central U.S. will offer an enhanced precipitation focus from
the Great Basin/Northern Rockies (including elevation snows) to
the Northern Plains/Upper Midwest/Great Lakes with cyclogenesis.
Subsequent southern stream upper trough and surface system
translation out from the Southwest may then focus moderate
rainfall/convection from the south-central U.S. to the Midwest
early next week in response to robust upper trough/low
amplification and frontal digging back over an again unsetted and
cooled West. Maximum temperatures there may decrease in some areas
to 10-20F below normal to offer potential for some record values.
This development would also foster widespread precipitation
chances over the West to include enhanced mountain snows.
Downstream, a warming Plains upper ridge later week shifts over
the east-central U.S. next week. WPC web links listed below
provide more specific information on the surface/500mb pattern and
sensible weather/hazards.
...Guidance Evaluation/Preferences...
The models seem to offer reasonably well clustered guidance
Fri/Sat considering flow complexity and a composite blend of the
latest GFS/ECMWF/UKMET/Canadian, the National Blend of Models
(NBM) and WPC continuity seems to offer a good forecast basis and
detail consistent with a mid-larger scale pattern with average to
above average predictability. The compatible 12 UTC GEFS/ECMWF
ensemble means and the NBM may prove a more suitable blend days
5-7 (Sun-next Tue) considering model run to run variances with
embedded systems and weather specifics, but forecast spread at
these longer time frames may still equate to a pattern with
average to above average predictability.
Schichtel
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