Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Sun Dec 04 2022

Valid 12Z Wed Dec 07 2022 - 12Z Sun Dec 11 2022

...Heavy rain threat from the southern Plains to the Mid-South
midweek to the central Appalachians/Mid-Atlantic later week in
active flow across much of the nation...


...Guidance/Predictability Assessment and Weather/Hazard
Highlights...

The WPC medium range product suite was primarily derived from a
composite of reasonably well clustered guidance from the 18 UTC
GFS and 12 UTC ECMWF/UKMET/Canadian models along with WPC
continuity and the 1 UTC National Blend of Models for Wednesday
into Friday in a pattern with seemingly improving/above average
predictability. The latest 00 UTC model runs generally remain in
line as well during this forecast period. There is a growing
signal for heavy rains from the southern Plains to the Mid-South
midweek with ejection into the flow of southern stream upper
trough and the experimental medium range WPC Excessive Rainfall
Outlook (ERO) continues to have a "Slight" risk area centered over
the region as also fueled by frontal pooling Gulf moisture/repeat
cells within the favorable right entrance region of the upper jet.
Activity may spread ENEWD to the central Appalachains/Mid-Atlantic
into Thursday/Friday, possibly aided Friday by uncertain/moderate
coastal flow genesis. There is also some potential for a swath of
snow/ice during this period on the cooled northern periphery of
this precipitation shield from the Midwest through the Northeast.
Meanwhile upstream, ample system energies digging southeastward
from the Gulf of Alaska are slated to work into the West
Thursday/Friday and renew moderately heavy precipitation chances
into the Northwest and northern California to include a threat for
enhanced terrain/mountain snows that should spread increasingly
inland over an unsettled West into the weekend. Transitioned model
guidance increasingly toward the GEFS/ECMWF ensemble means next
weekend in a period with quickly growing model forecast spread
that is mainly due to differences with aspects of the digging of
energy into the West and subsequent downsteam progression.
However, suspect the means are by nature are not amplified enough
given recent flow history and model trends, so still incorporated
into the forecast limited model guidance to compensate and provide
better system detail as warranted. The pattern also looks to offer
another emerging favorable setup for additional rainfall over the
east-central U.S. next weekend as western U.S. upper trough
energies work uncertainly downstream as return Gulf moisture
intercepts a developing/wavy frontal system. The pattern also
seems favorable for renewed precipitation into the Northwest again
next weekend as additional northeast Pacific system energies work
inland into the unsettled region.

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, experimental excessive rainfall
outlook, 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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml