Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 AM EDT Fri Nov 02 2018

Valid 12Z Mon Nov 05 2018 - 12Z Fri Nov 09 2018

...Guidance/Predictability Assessment and Pattern Overview/Weather
Threats...

The 00 UTC GFS trended strongly toward the 12 UTC ECMWF, but
differences and run-run variance remains with smaller scale
details. The WPC medium range product suite was mainly derived
from a blend of these models and respective/compatable ensemble
means.

Broad cyclonic flow/upper-level troughing spreads over much of the
lower 48 next week between upper ridges that hold over the eastern
Pacific and western Atlantic. The trough will be reinforced by a
series of shortwaves originating in the north Pacific that
potentially interact/amplify over the Plains with addition of
shortwave energy of polar/arctic origin. There is an increasing
threat for deepening low pressure to lift into the Midwest/Great
Lakes by next Tuesday then eastern Canada mid-later week. This
would force a precipitation focusing frontal system across the
central then eastern states. Colder Canadian air to dig into lower
48 in the wake of system passage supports organized snow on the
northwest system periphery, mainly over the Upper Midwest.

In this pattern much of the east-central U.S. will see more
widespread precipitation early next week as dynamic support aloft
combines with increasingly favoravble return thetae advection with
storm/frontal advance and deepening. An expanding areas of rain
will spread northeastward ahead of the system Mon-Wed with an inch
or more of rain possible over a large area. This includes the
Mississippi/Ohio/Tennessee Valleys, Midwest/Great Lakes, and the
East. Over the East, a lingering lead stationary front may
meanwhile push back toward the coast to further bring potential
for precipitation back to the I-95 corridor from the Southeast all
the way northward to New England. Later week more modest
precipitation may renew over the s-central/southern U.S./Gulf of
Mexico as additional shortwave energies dig into the base of the
longwave trough aloft and feed upon moisture pooled along a
stalled wavy/trailing front. Meanwhile, periods of moderate rains
and higher elevation snows will be possible for the Pacific
Northwest early-later next week, with snows spreading to the
Rockies as upper shortwaves and surface fronts traverse the region
to the lee of the eastern Pacific upper ridge.

Schichtel


WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes are found 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