Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
243 AM EDT Thu Oct 07 2021
Valid 12Z Sun Oct 10 2021 - 12Z Thu Oct 14 2021
...First winter storm of the season possible for parts of the
central and northern Rockies by early to middle next week...
...Guidance Evaluation/preferences...
For a medium range forecast, with one main exception there's
actually really good agreement through the entire period on the
overall large scale setup which features a shortwave/closed low
lifting through the southern Plains early next week, while
troughing amplifies over the West and a well defined low pressure
system emerges into the Central Plains by the middle of next week.
There remains some relatively minor timing and detail differences,
but these kinds of uncertainties may take until the short range to
resolve. Overall, the WPC forecast suite was derived from a
composite blend of the deterministic models, ensembles and
National Blend of Models for days 3-7. This maintains good
continuity with the previous WPC forecast helping to increase
confidence some in the pattern and relevant weather hazards. The
one main exception is over the Mid-Atlantic and Northeast Sun/Mon
where the 12 UTC ECMWF/Canadian and to a lesser extent ECMWF
ensembles wrap much more QPF inland from a western Atlantic low
than the GFS/UKMET/GEFS. WPC continuity, latest NHC guidance, and
latest 00 UTC guidance trends do not favor the 12 UTC
ECMWF/Canadian solution.
...Pattern Overview and Weather/Hazards highlights...
A slow moving frontal boundary and area of low pressure off the
East Coast, with limited tropical development probabilities as per
NHC, offers potential for some heavy downpours into coastal areas
of the Mid-Atlantic to the Northeast, especially Sun/Mon. The WPC
product suite minimizes heavier rainfall potential onshore
considering latest NHC system guidance and WPC continuity.
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. Amplifying southern stream
upper trough energy should act to focus moisture/instability to
fuel an increasingly favorable convection and organized rainfall
environment Sun/Mon for portions of the Plains, with the SPC
noting a severe weather area across the southern Plains on Sunday
in their day extended outlook. The system should then begin
lifting and shearing over the Midwest/Great Lakes on Tuesday, with
mainly light to moderate precipitation.
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 25-30 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 northern Rockies beginning on Sunday. A
low pressure system should eject out of the Rockies into the
Plains, with increasing confidence in potentially heavy snowfall
within an emerging deformation area on the back/west side of the
low. This could bring the first winter storm of the season to
portions of the central and northern Rockies. An axis of heavy
rainfall is possible around and to the north of the low, with some
mixing of snow not out of the question during the colder overnight
hours. Gusty winds may also be possible across the central and
northern Plains by Wednesday and Thursday of next week as the
surface low deepens through the central to northern U.S. and
further enhances precipitation. Across the central and southern
Plains, moderate to locally heavy rainfall is possible with
another threat for severe weather on Tuesday into Wednesday as
highlighted in the latest SPC extended outlook.
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