Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Sun Aug 11 2019
Valid 12Z Wed Aug 14 2019 - 12Z Sun Aug 18 2019
...Overview and Guidance/Predictability Assessment...
Early in the medium range period, low amplitude troughing will
prevail over the east as ridging once again builds centered over
the Southwest/Southern Plains. Another trough is expected to
approach the Pacific Northwest Wed and enter around Thu. It
appears the 00Z UKMET is too fast with the track of this trough by
Thu and especially Fri, and the 00Z CMC is weaker than other
guidance initially (though eventually looks similar to other model
guidance with its strength and position by Sat). The trough and
energy is expected to move eastward through the northwest and
north-central CONUS over the weekend, but the details are rather
uncertain, as its progression depends on the evolution of an upper
low moving southward in the vicinity of the Alaska panhandle on
Fri/Sat. Solutions diverge with this upstream feature especially
by Sat, and the 00Z ECMWF looks like an outlier with the GFS
having somewhat better run-to-run continuity. Thus, used a 06Z/00Z
GFS and 00Z ECMWF blend early on, with some incorporation of the
NAEFS and EC means. Leaned much more toward the means by the
weekend forecast and eliminated the 00Z ECMWF. Also of note is the
GFS spinning up a mid-level low by Sat along the eastern Gulf
Coast over its past several runs, possibly from the dying front at
the surface and likely convection in the vicinity. With the ECMWF
weaker and the usually aggressive CMC showing nothing, was not
willing to fully latch onto this feature yet.
The main change made to the fronts/pressures from the overnight
forecast was slowing down the low pressure/frontal system moving
through the Northern Plains over the weekend, due to models
trending slower with the shortwave entering the area.
...Weather Highlights/Threats...
A wavy lead frontal system will shift southward through the
eastern and central states, stalling out over the South/Southeast
later week. Widespread showers and thunderstorms including a
threat of local cell training/runoff issues are expected to move
southward from the Mid-Atlantic to focus into the Southeast/Gulf
Coast from midweek onward as deepened Gulf moisture streams into
the vicinity of the front. Upstream, upper trough amplification
over Northwest/northern Rockies mid-later this week and robust
system/height fall ejections into the north-central U.S. next
weekend should both provide dynamics and instabilities supportive
of periods of locally enhanced rainfall and thunderstorms.
Expect warmer than average pre-frontal temperatures for the Gulf
Coast states/Southeast into mid-later week. There is a threat of
excessive heat with widespread record high minimum temperatures
through Wed morning. Additionally, the Southwest to Southern
Plains should also experience hot temperatures through the period
under the upper high/ridge.
Tate/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