Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Wed Sep 04 2019
Valid 12Z Sat Sep 07 2019 - 12Z Wed Sep 11 2019
...Record heat to continue for the Lower Mississippi Valley/Gulf
Coast this weekend...
...Overview...
Upper ridging will remain anchored over the Lower Mississippi
Valley and Southeast this weekend and into next week. The West
will see lead troughing Saturday lift through the Great Basin
Sunday as reinforcing troughing comes into the Pac NW. With rising
heights over the Great Lakes/Northeast as Dorian exits, this will
take western systems eastward along the US/Canadian border. By
next Wednesday, troughing may linger along the west coast.
...Guidance Evaluation and Preferences...
Blend of the 12Z/18Z GFS and 12Z ECMWF/UKMET offered a good
starting point for most of the CONUS Sat-Mon as a front pushes off
the east coast but stops across the Tennessee Valley due to
ridging to its south. For Mon-Tue, GFS/ECMWF were close to their
means with the exiting High Plains low pressure that should move
ENE into the Great Lakes. In the West, uncertainty increases by
next Tue/Wed due to upstream timing/amplitude differences in the
guidance. This area has been much less predictable than elsewhere
in recent days and the GEFS mean and ECMWF ensemble mean become
out of phase by next Wednesday. Prefer to side more with the ECMWF
ensemble mean which favors continued (maybe reinforced) troughing
along the west coast rather than ridging per just the recent GEFS
mean.
...Sensible Weather...
A potent cold front will bring fall-like temperatures (10-20F
below average) to the High Plains/Upper Midwest this weekend as
many places rise only into the upper 50 and 60s. The Southern tier
of the CONUS from Texas eastward to Florida will generally see
well above average temperatures in the mid-90s to around 100F that
are forecast to tie or break record highs. The heat may temper
only a bit next week as temperatures stay in the middle and upper
90s from Texas to Georgia. Much of the West will see below average
temperatures under upper troughing.
Rainfall will dive through the Plains/Corn Belt this weekend with
additional rainfall moving into the Northwest. As the cold front
moves eastward early next week, rain will advance in tandem
through the northern tier states. Questions remain in how much
moisture will lift out of NW Mexico into the Southwest/Four
Corners region next week. The GFS/GEFS runs have been wetter than
the ECMWF/ECMWF ensembles so a middle ground solution was depicted
in the QPF progs for now especially along/north of I-40 in AZ/NM.
Fracasso
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