Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
209 AM EDT Sat Aug 03 2019
Valid 12Z Tue Aug 06 2019 - 12Z Sat Aug 10 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. A couple of cold fronts will sweep across the north central
and northeastern U.S. during the forecast period along the base of
the broad upper trough. Meanwhile upper ridging across the Four
Corners region should gradually weaken and slide east toward the
Southern Plains. Models/ensembles showed good agreement at the
larger scales through the medium range, but did show some
variability (perhaps slightly less than average) with respect to
the details of specific systems. Given the general large scale
agreement, a blend of the 12Z ECMWF/CMC/UKMET/18Z GFS was used as
a forecast starting point with a slowly increasing percentage of
ensemble mean (ECENS and GEFS) weighting during days 5-7 (Thu-Sat).
...Weather Highlights/Threats...
Monsoonal moisture will focus scattered showers and storms with
locally heavy rainfall over the Four Corners through much of 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 trailing end
of the frontal boundaries in the central U.S. The Pacific
Northwest will initially see high temperatures several degrees
warmer than average Tue-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 late in the week in the wake of the surface cold fronts,
with high temperatures expected to be around 5 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