Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1058 AM EST Sun Nov 04 2018

Valid 12Z Wed Nov 07 2018 - 12Z Sun Nov 11 2018

...Overview...

Broad cyclonic flow aloft will remain anchored over most of the
lower 48 this week into the weekend as embedded systems pass
through the large scale mean trough. An organizing Southern Plains
system will drop out of the Intermountain west and lift into the
Great Lakes Friday with some wintry weather on its north side.
Cooler than average temperatures are favored for most of the lower
48 except the west/east coasts and along the Gulf Coast Wed/Thu
(before a cold front moves through).


...Guidance/Predictability Assessment and Preferences...

Main storm of interest will be the Midwest cyclone Friday where
the models/ensemble vary on timing/strength of the low/front as
well as the influence of a stalled front along the coast. The GFS
runs remained a bit quicker than the ensemble means, which were
quicker than the 00Z ECMWF and UKMET (slowest). Though the system
may have reason to modestly deepen and track slower northeastward,
lead system in the short range has trended quicker in the broad
flow as individual shortwaves may have a harder time trying to
slow the entire pattern. Thus, opted to stay near the middle of
the guidance via the ensemble means for now. Once the low lifts
into Canada and the front clears the east coast (and into southern
Florida), high pressure will slide into the east with perhaps
another northern stream system dropping through the High Plains.
06Z GFS and 00Z parallel GFS (FV3-GFS) were reasonable
deterministic weights with the ensemble means by next weekend as
the 00Z ECMWF appeared much too strong over the northeastern
Pacific with an incoming low into western Canada Sat/Sun.


...Weather Highlights/Threats...

Generally light but occasional modest rain/snow in the west tied
to the incoming shortwave and surface cold front (south) and
stationary front (north) will exit the Rockies onto the Plains
where ENE flow around a surface high to the north may support a
swath of light snow through the central Plains (eastern CO across
NE/KS northeastward). To the south, Gulf moisture will support
modest rainfall (potentially locally heavy via embedded
convection) from the lower Mississippi Valley eastward into the
Southeast as the front progresses eastward. As the front clears
the east coast, lake-effect snow is likely (potentially several
inches) with cold temperatures aloft atop mild lake temperatures
(near or under freezing over land) and generally NW flow.
Temperatures will be most anomalously cool around the Upper
Midwest/Great Lakes (5-20F below average) as well as Texas behind
the cold front. This may be near record cold maximum temperatures
for some locations in the Midwest.

Fracasso


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