Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Sun Aug 11 2019
Valid 12Z Wed Aug 14 2019 - 12Z Sun Aug 18 2019
...Overview and Guidance/Predictability Assessment...
Quasi-zonal flow over the northern half of the lower 48 will
amplify later this week as a deeper trough digs into the West
Coast and ridging strengthens over the south-central U.S. This
seems likely to favor mean troughing downstream in the eastern
U.S. Energy from the western trough may split by next weekend,
with part moving eastward and part hanging back along the western
U.S, though scenario details have lower predictability given ample
recent run to run continuity issues. A composite blend
incorporating the 18 UTC GFS/GEFS mean and 12 UTC ECMWF/ECMWF
ensemble mean was mainly used as the starting point for the WPC
medium range product suite, leaning heavily on ensembles due to
the continued smaller-scale uncertainties in the flow. Overall,
this blend provided good WPC product continuity.
...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.
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