Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
333 PM EDT Fri Aug 02 2019
Valid 12Z Mon Aug 05 2019 - 12Z Fri Aug 09 2019
...Overview and Guidance/Predictability Assessment...
Upper ridging migrating slowly westward from the Gulf of Alaska to
the Bering Sea through the forecast period favors troughing in the
vicinity of the Pacific Northwest and downstream across the Great
Lakes. Meanwhile upper ridging across the Four Corners region
should gradually weaken. Models/ensembles showed good agreement at
the larger scales through the medium range, but did show some
variability with respect to the details of specific systems, but
less than usual considering the amplified pattern. Given the
general large scale agreement, a blend of the 00Z
ECMWF/CMC/UKMET/06Z GFS was used as a forecast starting point with
a slowly increasing percentage of ensemble mean (ECENS and NAEFS)
weighting during days 5-7 (Wed-Fri). Considering the agreement,
kept the weighting under 50% for the pressures, fronts, winds, and
500 hPa graphics. The remainder of the grids were weighted
towards the 12z National Blend of Models.
...Weather Highlights/Threats...
Monsoonal moisture will focus scattered showers and storms with
locally heavy rainfall over the Four Corners next week as the
upper high weakens. Elsewhere, rainfall will follow the front in
the north but be more scattered and diurnally driven in the
Southeast. Areas of more organized convection and heavy rain are
possible across the central U.S. along the cold front. The Pacific
Northwest will initially see high temperatures several degrees
warmer than average Mon-Wed before a cooling trend arrives later
in the week as the upper low begins to move inland. Relatively
cool temperatures are also expected to move into the north central
U.S. by Wed-Fri in the wake of the surface cold fronts, with high
temperatures expected to be 5-10 deg F below average.
Roth/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
Hazards:
- Heavy rain across portions of the Central/Southern Plains, the
Middle/Lower Mississippi Valley,
the Tennessee Valley, and the Ohio Valley, Mon-Fri, Aug 5-Aug 9.
- Flooding possible across portions of the Central Plains and the
Middle Mississippi Valley.
- Flooding occurring or imminent across portions of the Central
Plains, the Lower Mississippi
Valley, and the Northern Plains.
- Flooding likely across portions of the Central Plains, the
Middle Mississippi Valley, and the
Southern Plains.
- Heavy rain across portions of mainland Alaska, Mon-Tue, Aug
5-Aug 6.
- High winds across portions of mainland Alaska, Mon-Tue, Aug
5-Aug 6.
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