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FXUS02 KWBC 310629

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
228 AM EDT Sat Oct 31 2020

Valid 12Z Tue Nov 03 2020 - 12Z Sat Nov 07 2020

...Heavy Precipitation for the Pacific Northwest...


An anomalously strong and cold upper trough ejects from New
England Tue as fast zonal flow develops upstream over the CONUS.
Upper trough amplification offshore the Pacific Northwest next
week will direct deep moisture into western WA. There is a good
signal for a heavy precipitation focus in the Olympics/Cascades by
Tue/Wed, with lowering snow levels before shifting into OR/CA and
the northern Rockies later next week as the vigorous upper
trough/height falls work inland over the West. Otherwise, dry
conditions will prevail for much of the rest of the lower 48
except for parts of FL in protracted easterly post-frontal flow
well to the north of yet another potential Caribbean tropical
system being monitored for development by the NHC.

...Guidance Evaluation/Preferences...

The WPC medium range product suite was primarily derived from a
composite blend of the latest and well clustered solutions from
the GFS/ECMWF, GEFS/ECMWF ensemble means, the National Blend of
Models and WPC continuity in a pattern with above normal
predictability near the lower 48 day 3 into 7.

...Weather/Hazard Highlights...

Cold air may threaten some temperature records in the Northeast
into Tue as lake enhanced snows linger downwind of Lake Ontario.
Below normal temperatures over the East will moderate in the first
half of the week as the above normal temperature across The West
expand east to the Plains/Midwest/Northeast. Some records are
possible over CA/AZ. Heaviest precipitation is expected over the
Pacific NW, particularly WA Tue/Wed as fueled by an atmospheric
river. Rains and lowering elevation snows will spread over the
Northwest to the Northern Rockies and north-central CA/Great Basin
later next week. Rainfall potential also increases into FL next
week in easterly fetch well to the north of another possible
Caribbean tropical system.


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

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