Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
212 AM EDT Sun Aug 04 2019
Valid 12Z Wed Aug 07 2019 - 12Z Sun Aug 11 2019
...Overview and Guidance/Predictability Assessment...
A slow-moving upper low initially off the West Coast is expected
to move inland by next weekend. Downstream, an upper ridge
initially centered across the Four Corners region is forecast to
shift eastward into the Southern Plains. Meanwhile, broad cyclonic
flow (traversed by a couple shortwaves and surface cold fronts)
will persist from the Upper Midwest/Great Lakes to the Eastern
Seaboard on the southern periphery of an upper low progressing
across northeastern Canada. A blend of the 12Z ECMWF/CMC and 18Z
GFS was used for the forecast during days 3-5 (Wed-Fri), with a
shift toward majority ECENS and GEFS ensemble mean weighting
during days 6-7 (Sat-Sun). The largest model differences were
later in the period with respect to a shortwave crossing the Great
Lakes/Northeast Sat-Sun, and with the system moving inland across
the Pacific Northwest. With both of these features relatively high
spread with respect to the details of timing/structure lended to
favorability of ensemble mean solutions.
...Weather Highlights/Threats...
The central U.S. will be the focus for areas of deeper convection
through the forecast period, along the trailing end of a couple
frontal boundaries that move into the Central/Southern Plains and
then stall. Models show a signal for an area of heavy rainfall,
perhaps associated with a couple rounds of intense convection from
portions of the Central Plains into the Mid-Mississippi Valley
Thu-Fri. Elsewhere, showers and thunderstorms should focus across
the Northeast and portions of the Mid-Atlantic Wed-Thu along/ahead
of a cold front. Farther west, monsoonal moisture will persist
with diurnal showers and thunderstorms across portions of the
Southwest and southern/central Rockies. Showers/storms may also
begin to spread into the northern Great Basin/northern Rockies by
next weekend as the Pacific upper trough moves inland. In terms of
temperatures, expect hot conditions across the Southern Plains
beneath the upper ridge, with high temperatures 5 to 10 deg F
above average daily. Below average temperatures should spread into
the Pacific Northwest by next weekend in association with the
upper trough, with highs expected to reach 5 to 10 deg below
average.
Ryan
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