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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 0616Z Oct 16, 2018)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
216 AM EDT Tue Oct 16 2018

Valid 12Z Fri Oct 19 2018 - 12Z Tue Oct 23 2018

...Pattern Overview...

Reinforced upper troughing will persist in the eastern half of the
CONUS while ridging is forecast to linger over the Pacific
Northwest. A series of fairly weak Canadian fronts will swing
through the Great Lakes to maintain below average temperatures and
spark off some rain/snow showers especially in favored lake-effect
areas. The strong upper ridge over Florida will only slowly weaken
by next week and get squashed into Cuba. On its west side will be
a stalled front off the Texas coast which will keep a daily chance
of rainfall in the forecast, especially southern Texas. Finally, a
lost upper low near Southern California will seek an exit route
through the Great Basin early next week, helping to wring out some
light showers.

...Guidance/Predictability Assessment...

An operational model consensus continues to represent individual
features well for Fri-Sun. After that time model runs begin to
show greater shortwave differences among each other and/or in
consecutive runs, favoring a trend toward the ECMWF ensemble mean
and GEFS mean. Pacific front will attempt to move into
Washington/Oregon late next Tuesday but the ensembles differ
quicker/slower (ECMWF/GEFS, respectively). ECMWF and its ensembles
have had a tendency to break down the western ridge too quickly at
that time range but a shift northward in the positive height
anomaly could allow for an opening into the Pac NW as quick as the
ECMWF ensemble mean (perhaps not as quick as the 12Z/15 ECMWF).
For now, a modest middle ground sufficed.

...Weather Highlights/Threats...

Above average temperatures are favored in the west outside the
influence of the upper low, generally 5-10F above average.
Troughing in the east and cloud cover over Texas will keep
temperatures below average there but with a little variation
around frontal passages. Some areas will see near record warmth
(WA/OR and FL) with more widespread cool temperatures and chilly
afternoon highs around the Lakes into the Northeast (40s/50s).

Expect highest 5-day rainfall totals over portions of Texas and
near the western Gulf Coast, in the vicinity of an inverted trough
and to the northwest of a stationary boundary in the western Gulf.
Some of this southern Plains moisture may extend northeastward
along a cold front crossing the East during the weekend. The
lingering upper low in the Southwest will support rain and
possibly high elevation snow showers mostly focused on/along the
higher terrain while a stationary front across Florida will keep
daily shower/storm chances in the forecast. Over the Great
Lakes/Northeast lake-effect precipitation will start anew this
weekend behind a cold front and then again late in the forecast.
Coastal WA/OR will see rain develop and expand inland starting on
Monday and continuing on Tuesday, depending on the speed of the


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