Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 AM EDT Sun Sep 15 2019
Valid 12Z Wed Sep 18 2019 - 12Z Sun Sep 22 2019
...Overview and Guidance Evaluation/Preferences...
Models and ensembles offer a reasonably similar and amplified
larger scale pattern over the lower 48 and vicinity for much of
the upcoming medium range period. Forecast spread and uncertainty
for small-mid scale embedded features has also improved,
bolstering forecast confidence. Flow will be highlighted by an
amplified and unsettling mean upper trough over the West and
sprawling/hot late summer east-central states upper ridging. The
WPC medium range product suite was primarily derived from a
composite blend of the 18 UTC GFS/GEFS, 12 UTC ECMWF/ECMWF
ensemble means and the National Blend of Models.
...Weather Highlights/Threats...
Tropical Storm Humberto continues to be forecast by NHC to turn
east and away from the southeast coast as a hurricane over the
next couple of days.
A series of amplified upper troughs and lead surface frontal
systems will dig into the West then eject northeastward over the
north-central U.S. this week. This will bring widespread rains
(some very high elevation snow) to the Northwest. Activity spreads
south into northern CA and out through the northern/central Great
Basin/Rockies. An organized convective focus with locally heavy
downpours shifts to the Upper Midwest with leading shortwave
energy/height fall passage into midweek and modest/local potential
with southward and eastward progressing surface frontal systems.
Increased moisture inflow may lead to some record high minimum
temperatures. The upstream pattern meanwhile reloads again over
the West to reach the north-central states again next weekend.
In this pattern expect subtropical moisture out of Mexico on
southwest flow aloft over the Southwest/Four Corners states. This
moisture may fuel support for aforementioned potential convection
downwind into the north-central U.S. Strong ridging downstream
over the east-central U.S. will favor well-above average
temperatures next week with some near record Deep South heat.
Nearby in the western Gulf of Mexico, a trough/wave associated
with an upper low favors a potentially heavy over coastal Texas
midweek and weak steering aloft may allow this area of rain to
persist through late week.
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