Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Wed Sep 29 2021
Valid 12Z Sat Oct 02 2021 - 12Z Wed Oct 06 2021
...Overview...
The slow-moving front extending across the Great Plains should
begin to move eastward as the medium range period begins on
Saturday, spreading scattered showers/thunderstorms and possibly
embedded heavy rain eastward across the Ohio Valley on Sunday and
Monday, and into the East Coast Tuesday and Wednesday. Over the
Pacific Northwest, the next moisture plume is forecast to slowly
edge into the region by early next week. Meanwhile, some
monsoonal moisture appears to make a return across the
Four-Corners region by early next week.
...Guidance Evaluation/Preferences...
Model guidance are coming into better agreement with respect to
shifting the slow-moving frontal boundary across the Plains
progressively eastward beginning on Saturday. Both of the ECMWF
and GFS have reached relatively good agreement on this eastward
shift, with a more typical slightly faster GFS verses the slightly
slower ECMWF. The slower ECMWF favors a weaker low pressure wave
moving across the central Plains behind a main low pressure center
forecast to drift southeastward across the Great Lakes by both
models. By next Tuesday, the 00Z ECMWF develops this system over
New England ahead of an amplifying upper low over the Great
Lakes--a scenario that is not yet supported by its ensemble mean.
Therefore, a consensus of the 00Z ECMWF/00Z EC mean with the 06Z
GFS/GEFS was adopted to handle this system, with more weights
given to the EC mean for Days 5-7 relative to its deterministic
component. This blend should also provide a proper handle to the
next system of interest moving into the Pacific Northwest. The
00Z CMC has not been included in the blend due to significant
deviation from the GFS-ECMWF consensus in the general synoptic
pattern across the U.S. through much of the medium-range period.
...Weather and Potential Hazards...
Scattered showers and thunderstorms can be expected to spread
gradually eastward across the Ohio and Tenessee Valleys on Sunday
and Monday ahead of a frontal system, with some embedded heavy
rain possible. Some showers and storms are expected to move
through the Deep South as well. Steady rain is now forecast for
New England Sunday and Monday north of a stationary front. The
rain could linger into Tuesday as a low pressure center drifts
across the Great Lakes along the stationary front toward the
northern Mid-Atlantic region. The scattered showers and storms
should then affect much of the eastern U.S. Monday and Tuesday and
possibly into Wednesday as a cold front slowly moves across and
could reach the East Coast on Wednesday. Meanwhile, some
monsoonal moisture appears to make a return over the Four-Corners
region by early next week as an upper low off the southern
California coast is forecast to move onshore. Over the Pacific
Northwest, the next moisture plume ahead of a positively-tilted
trough is forecast to slowly edge into the region by early next
week.
Cooler than normal temperatures are forecast for much of the
southern tier states due to clouds and precipitation followed by a
cold frontal passage across the Deep South. Meanwhile, warmer
than average temperatures are forecast for the Midwest, Ohio
Valley and the East Coast this weekend near/ahead of a low
pressure system moving through the Great Lakes, though they are
likely to moderate to near normal by Monday. A more significant
warm-up is now forecast for the northern Plains towards the middle
of next week as afterrnoon temperatures are expected to peak well
into the 80s.
Kong
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
Hazards:
- Flooding occurring or imminent across portions of the Great
Lakes.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat, Oct 2.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Sat, Oct 2.
- High winds across portions of mainland Alaska and the Aleutians,
Mon-Tue, Oct 4-Oct 5.
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