Skip Navigation Links 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center



Follow the Weather Prediction Center on Facebook Follow the Weather Prediction Center on Twitter
NCEP Quarterly Newsletter
WPC Home
Analyses and Forecasts
   National High & Low
   WPC Discussions
   Surface Analysis
   Days ½-2½ CONUS
   Days 3-7 CONUS
   Days 4-8 Alaska
   Flood Outlook
   Winter Weather
   Storm Summaries
   Heat Index
   Tropical Products
   Daily Weather Map
   GIS Products
Current Watches/

Satellite and Radar Imagery
  GOES-East Satellite
  GOES-West Satellite
  National Radar
Product Archive
WPC Verification
   Medium Range
   Model Diagnostics
   Event Reviews
   Winter Weather
International Desks
Development and Training
WPC Overview
   About the WPC
   WPC History
   Other Sites
Meteorological Calculators
Contact Us
   About Our Site is the U.S. Government's official web portal to all federal, state, and local government web resources and services.
Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 1556Z Oct 16, 2018)
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
Abbreviations and acronyms used in this product
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Tue Oct 16 2018

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

...Pattern Overview...

A mean trough aloft will persist over eastern North America
downstream from a Pacific Northwest/western Canada ridge. The
gradual approach of a northeastern Pacific upper trough will begin
to push the ridge axis a little eastward by the first part of next
week.  Under the eastern upper trough a series of Canadian fronts
will swing through the central-eastern states 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 slowly weaken by next week and get squashed into
Cuba. On its west side will be a stalled front off the Texas coast
and nearby surface trough which will keep a daily chance of
rainfall in the forecast, over southern Texas in particular.
Finally to the south of the Northwest ridge, a weak upper low near
southern California will likely eject into the Great Basin early
next week with the approach of more progressive Pacific flow,
helping to wring out some light showers.

...Guidance/Predictability Assessment...

Note that 00Z CMC/CMC ensemble runs were not available for the
forecast.  Remaining guidance in the 00Z-06Z cycles offer better
than average agreement, and even by day 7 Tue operational run
differences fall within typical error range.  By late day 7 the
06Z GFS/00Z ECMWF trend a bit toward the deeper/sharper side of
the spectrum with the shortwave nearing the East Coast but still
compare acceptably to the overall pattern thus meriting inclusion
for the forecast.  ECMWF ensembles as a whole are still a little
more eager to lower heights along West Coast late in the period
but the operational 00Z ECMWF has made a favorable adjustment,
toward slower arrival of shortwave energy than the 12Z/15 run.

Due to an initial piece of Four Corners energy that the 00Z ECMWF
pulls into the Northwest Fri-Mon in a strong low-confidence
fashion (somewhat more sheared in the 00Z UKMET), the preferred
days 3-5 Fri-Sun model blend included the past two ECMWF runs
along with the 00Z/06Z GFS and 00Z UKMET.  Days 6-7 Mon-Tue
incorporated 40-50 percent total weight of the 06Z GEFS/00Z ECMWF
mean to temper timing differences that arise among the GFS/ECMWF. 
Due to the aforementioned issue with the old 12Z ECMWF near the
West Coast, that run was removed from the blend after day 5.  The
resulting forecast yielded modest and typical run-to-run
detail/timing adjustments for individual features but good
continuity overall.

...Weather Highlights/Threats...

Expect above average temperatures over much of the western U.S.
away from the influence of the southern upper low, generally 5-10F
above average but with some locally higher anomalies over parts of
the Northwest/extreme northern Rockies. Upper troughing farther
east and cloud cover over Texas will keep temperatures below
average over a broad area from the southern Plains into the
Northeast. Those two areas should see the greatest negative
departures from normal on one or more days. Frontal passages will
provide some daily variation in temperatures. A few locations
could see readings near record values for warmth over WA/OR and FL
while a few daily records for cool highs may be possible over the
Great Lakes/East Coast regions.

Highest 5-day rainfall totals will be 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, though
with some lingering uncertainty over precise rainfall amounts. The
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
with the passage of a weak system. Coastal WA/OR will see
light-moderate rain develop and expand inland early next week as
upper troughing approaches.


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