Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
236 AM 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 relatively good
agreement at the larger scales through the medium range, but did
show some variability with respect to the details of specific
systems. An upper low initially off the Pacific Northwest coast
should begin to move inland by late next week, but solutions
differ on the exact timing of this. Farther east, several
shortwaves are expected to rotate through the broad cyclonic flow
from the north central to the northeastern U.S. moving a couple
cold fronts into the central/eastern states. Models show some
differences on the timing and amplitude of these features. Given
the general large scale agreement, a blend of the 12Z
ECMWF/CMC/18Z GFS was used as a forecast starting point for days
3-4 (Mon-Tue), with a gradual transition to majority ensemble mean
(ECENS and GEFS) weighting during days 5-7 (Wed-Fri).
...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.
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