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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 0658Z Oct 17, 2018)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Wed Oct 17 2018

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

...Pattern Overview...

Troughing in the Great Lakes this weekend will be reloaded next
Tue/Wed while the western ridge slowly/stubbornly relents.
Subtropical ridging over Florida will squash into Cuba as a weak
upper low over California drifts through the Great Basin. The
pattern is rather cool/dry for much of the lower 48 besides Texas
and Florida in the vicinity of a stalled front through the Gulf of

...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/Canadian/UKMET
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 Pac NW which is rather
uncharacteristic in the longer term, but has been noted recently.
Preferred to stick closer to the slower cluster of solutions
around the 18Z GEFS mean that included the 12Z GFS/ECMWF.

...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.


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