Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Wed Aug 14 2019
Valid 12Z Sat Aug 17 2019 - 12Z Wed Aug 21 2019
...Overview and Guidance/Predictability Assessment...
Models and ensembles agree at larger scales that upper ridging
will build again into the Southwest near the New Mexico/Texas
border by early next week as troughing digs down into the
Northeast Pacific offshore British Columbia. Broad cyclonic flow
will persist over southeastern Canada and through the Great
Lakes/Northeast. The models and ensembles have converged toward a
similar idea of the high-latitude flow out of Alaska/NW Canada
that determines the shape/strength of the Northeast Pacific
troughing. Flow depiction in this region has been particularly
uncertain and run-run inconsistent in recent guidance. A composite
blend of the latest runs of the GFS/ECMWF and increasingly their
ensemble means over time seems to offer a good forecast starting
point amid lingering uncertainty in system details. This features
a stationary Southeast boundary, fronts moving through Canada and
the U.S. northern tier, and western Canada to Northwest U.S. mean
troughing.
...Weather Highlights/Threats...
Heavy rain potential will persist this weekend into next week from
the lower Mississippi Valley eastward in the vicinity of the
Southeast U.S. stalled front, spreading modestly inland to the
Tennessee Valley/Mid-South later period with return flow. To the
north, shortwave passages along lead fronts will focus weeked
convection from the Upper Midwest/Great Lakes eastward to the Ohio
Valley and Northeast/Mid-Atlantic early-mid next week.
In this pattern, temperatures will be above normal in the
Southwest/Southern Plains for much of the period and some daily
records will be possible with upper ridge expansion.
Schichtel
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are 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