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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1550Z Oct 17, 2018)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1150 AM EDT Wed Oct 17 2018

Valid 12Z Sat Oct 20 2018 - 12Z Wed Oct 24 2018

...Pattern Overview...

A relatively benign pattern shapes up the medium-range period
through next Wednesday, with troughing persisting in the Northeast
while a Rex block pattern develops and lingers in the West.  The
wettest part of the country should be along the Gulf Coast where
moisture continues to circulate around a subtropical high centered
over Cuba.  The Pacific Northwest will see the next batch of
precipitation arriving toward the middle of next week with little
wintry weather expected in the higher elevations.


...Guidance/Predictability Assessment...

Models and ensembles continue to offer good clustering through the
next 5-6 days with expected timing/amplitude differences by next
Tue/Wed.  A deterministic blend of the GFS/ECMWF offered a good
starting point close to continuity for Sat-Mon as a lead and
secondary cold front push off the East coast and another Canadian
front dips into the western Great Lakes.  By next Tue/Wed an
approaching Pacific system (or couple of systems) will eventually
break the ridge over the West, but the ECMWF ensembles remain
quickest to lower heights into the Pacific NW which is rather
uncharacteristic in the longer term, but has been noted recently.

Some spreads in the model solutions begin to show up on days 6 and
7 near the Canadian border regarding the cold high pressure system
dipping into the Great Lakes and the NE U.S.  The 00Z ECMWF now
shows a pressure pattern in closer agreement with the GFS, which
has been showing better consistency in that region.  Therefore,
the WPC morning grid file package is a consensus between the 00Z
ECMWF/EC mean, 00Z and 06Z GFS, 00Z GEFS with more of the ensemble
means incorporated for days 6 and 7.

...Weather Highlights/Threats...

The Pacific Northwest will see several days of above average
temperatures and dry conditions through the weekend.  Rain chances
will increase next week starting late Monday as the first cold
front approaches the coast.  Warm antecedent temperatures will
preclude snow from all but the highest elevations, but that will
change as cooler air works its way eastward.  Rain will become
widespread and moderate to locally heavy by midweek next week. The
rest of the CONUS will see near to below average temperatures with
the core of the coolest air from Texas northeastward to the
Northeast/New England.  Even Florida will slowly trend back toward
more typical late October temperatures in the upper 70s (north) to
mid 80s (south).

Coastal Texas has the highest probability of the greatest amount
of precipitation east of the Rockies due to an initial and then
subsequent stationary boundary through the Gulf next to an
inverted trough.  Though most of this may stay offshore, areas
near Brownsville may see several inches of rain over the period. 
Much less precipitation is expected elsewhere with each frontal
passage except for perhaps Florida with strong easterly flow.
Coastal WA/OR will see light-moderate rain develop and expand
inland early next week as upper troughing approaches with several
inches possible along the immediate coast by next Wednesday.


Kong/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