Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
252 AM EDT Wed Oct 06 2021
Valid 12Z Sat Oct 09 2021 - 12Z Wed Oct 13 2021
...Guidance Evaluation/preferences...
The WPC medium range product suite was primarily derived from a
composite model and ensemble blend days 3-7 with the 18 UTC
GFS/GEFS Mean 12 UTC ECMWF/ECMWF ensemble means and the 01 UTC
National Blend of Models prominantly weighted along with WPC
continuity. Guidance forecasts are overall reasonably well
clustered with the mid-larger scale pattern evolution into next
week, bolstering forecast confidence to a degree, but tempered by
continued run to run variability with the details and timings of a
multitude of complex embedded systems in two streams. A composite
of the latest 00 UTC model and ensemble suite still seems in line
with this forecast plan. In particular, the 00 UTC UKMET has
trended in this direction versus an outlier 12 UTC earlier run.
...Pattern Overview and Weather/Hazards highlights...
While a lingering rainfall axis will continue into the weekend
from the Mid-Atlantic/Central Appalachians to the Great Lakes, the
focus this weekend into next week should shift to the
coast/offshore where a frontal boundary and area of low pressure,
with limited tropical development probabilities, could bring some
heavy downpours to portions of the coastal Mid-Atlantic/Southeast.
Upstream, a front lifting through the north-central U.S. will
bring moderate to locally heavy rainfall to parts of the northern
Plains/Upper Midwest this weekend. Amplified approach of southern
stream upper trough energy underneath over the south-central
Plains and Mid-Lower MS Valley should act to focus
moisture/instability to fuel an increasingly favorable convection
environment Sun/Mon, lifting and shearing over the Midwest/Great
Lakes Tue.
Out West, moderate to heavy rainfall and mountain snow is possible
across parts of the Pacific Northwest this weekend, with moisture
shifting southward and inland with a wavy/lead front. Deep
troughing and closed upper low development down over the
Southwest/Great Basin into early-mid next week will bring much
below normal temperatures behind the cold front with daytime highs
as much as 20-25 degrees below normal across much of the interior
West well into next week. This would support lowering snow levels
in the mountains with potential for decent snow accumulations in
the higher terrain of the north-central Rockies and in an emerging
deformation area with the closed low. Ample upper trough/low
energies slated to shift from the West/Rockies into the Plains
next midweek would foster cyclogenesis/frontogenesis and emerging
convective rainfall fueled by building moisture/instability.
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