WPC Medium Range Archive
Medium Range Products Valid On:
(Day 7 PMDEPD: Valid 09/17/2019 to 09/21/2019)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1204 PM EDT Sat Sep 14 2019
Valid 12Z Tue Sep 17 2019 - 12Z Sat Sep 21 2019
...Overview and Guidance Evaluation/Preferences...
The latest (00Z/06Z) global suite and ensemble members have decent
agreement over the CONUS through next week and the persistent
ridge over the southeastern states...as well as keeping Humberto
well off the southeast coast. Run to run consistency has been
lacking among the global suite and the greatest differences in the
latest suite are with the flow pattern over the northeast Pacific
starting on Wednesday/Day 4. This leads to wildly different
deterministic solutions from the 00Z/06Z GFS with a strong ridge
persisting the Gulf of Alaska and 00Z ECMWF bringing a potent
through through that area by Saturday/Day 7. Multi-day
teleconnections for the strong eastern CONUS ridge signal
troughing in The West, but any particular day a week out could
Furthermore the 00Z UKMET greatly develops the western Gulf
tropical wave present in most guidance into a low and maintains
its strength through the Day 5 limit available at WPC.
Accordingly, the WPC medium range product suite was primarily
derived from the deterministic 06Z GFS/00Z ECMWF/00Z CMC for Days
3 and 4, then heavily toward ensemble means for Days 5-7. The
varied flow pattern off the West Coast for Days 6 and 7 was
handled with a blend of the 00Z ECENS and 00Z NAEFS means.
Tropical Storm Humberto continues to be forecast by NHC to turn
east and away from the southeast coast as a hurricane.
The first shortwave will push across the northern Plains Tuesday
night with some thunderstorm chances. In the Pacific Northwest, a
cooling surface front and subsequent upper trough will bring a
widespread chance of rain (some very high elevation snow) to the
region into Wednesday. This will spread through the
northern/central Great Basin/Rockies and into far northern CA
before pushing to the northern Plains/Upper Midwest Friday where
an increasingly active convective signature becomes evident as the
trough takes on a negative tilt.
Increased moisture inflow in advance of the first front may lead
to record high minimum temperatures over the northern Plains
Tuesday and the Upper Midwest Wednesday. Temperatures drop below
normal over the northern Plains behind the first system during the
midweek before raising ahead of the next system late in the week.
Meanwhile, expect subtropical moisture out of Mexico on southwest
flow aloft down over the Southwest/Four Corners states. Strong
ridging downstream over the east-central U.S. will favor
well-above average temperatures next week with some near record
Deep South heat.
In the western Gulf of Mexico, a trough/wave associated with an
upper low favors a potentially heavy over coastal Texas into
Wednesday. Weak steering aloft may allow this area of rain to
persist through late week.
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: