Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Tue Aug 13 2019
Valid 12Z Fri Aug 16 2019 - 12Z Tue Aug 20 2019
...Overview and Guidance/Predictability Assessment...
Upper ridging is forecast to build again into the Southwest near
the New Mexico/Texas border 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 but with generally above average
heights. The models/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. The 00Z
runs of the GFS/ECMWF and their ensemble means (slight preference
toward 00Z NAEFS vs the 00Z GEFS mean) offered a good starting
point amid lingering uncertainty in system details. This will
feature a stationary boundary in the Southeast, a defined front
moving through Canada and the northern tier, and western Canada
troughing toward the Northwest.
...Weather Highlights/Threats...
Heavy rain potential will persist from late this week through the
weekend from the lower Mississippi Valley eastward in the vicinity
of the stalled front in some areas, but otherwise scattered
rain/storms will be likely for the central/northeastern Gulf
Coast. ECMWF appears to be overzealous on precipitation due in
part to a nearly stationary mid-level reflection but still aligns
with the highest probabilities of heavier rain. To the north,
shortwave along the front may favor heavier rain through the Corn
Belt out of the short range Friday. Thereafter, highest rain
chances will push eastward into the Ohio Valley and eastern states
as weak troughing settles through the Great Lakes. Temperatures
will be above normal in the Southwest/Southern Plains and into the
Ohio Valley/Mid-Atlantic/Southeast for much of the period. Some
daily record highs will be possible over Texas this weekend and
perhaps Arizona next Tuesday as the ridging expands. Cooler than
normal temperatures are favored in the Northwest into Montana and
the northern Plains as cooler air pushes in over the weekend.
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
Hazards:
- Heavy rain across portions of the Central Plains, and the Middle
Mississippi Valley, Fri-Sat, Aug 16-Aug 17.
- Heavy rain across portions of the Southeast, Fri-Sun, Aug 16-Aug
18.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Excessive heat across portions of the Southern Plains, Fri-Tue,
Aug 16-Aug 20.
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