Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
211 AM EDT Tue Jul 02 2019
Valid 12Z Fri Jul 05 2019 - 12Z Tue Jul 09 2019
...Overview and Guidance/Predictability Assessment...
Typical summer pattern expected across the CONUS during the medium
range. Downstream of a Rex block across the North Pacific,
moderately progressive flow will pass between a building upper
ridge across the CONUS southern tier, and a broad upper low near
Hudson Bay. A shortwave crossing from the Northern Plains Fri to
the Great Lakes/Northeast Sat-Sun is expected to push a cold front
southward through the central U.S. and eastward across the
Midwest/Great Lakes, Ohio Valley, and eventually off the Eastern
Seaboard. The trailing end of this frontal boundary is expected to
stall from the Southern Plains to the Southeast, lingering into
early next week. Meanwhile, shortwave energy diving south on the
eastern periphery of the Alaska ridge is expected to reach the
Pacific northwest by the weekend, moving east across the northern
Rockies through early next week.
A blend of the ECMWF/GFS/CMC was used as a forecast starting point
during days 3-4 (Fri-Sat). The CMC dropped starting on day 5 (Sun)
as it became slower than consensus with the shortwave energy
moving into the Pacific Northwest. Otherwise, these solutions
handled the shortwave and cold front crossing the central/eastern
U.S. during that time frame similarly. During days 6-7 (Sun-Mon)
weighting of ECENS/GEFS ensemble means was gradually increased to
comprise a majority of the forecast weighting. Model differences
persist as to how quickly shortwave energy in the Pacific
Northwest/northern Rockies will move eastward into the Plains,
with the ECMWF consistently a bit faster than the GFS. Additional
shortwaves moving south across central Canada on the western side
of the mean upper low, and potential interactions with the
shortwave energy across the northern CONUS further reduce
predictability, lending to the greater use of ensembles by that
time period.
...Weather Highlights/Threats...
Numerous showers and thunderstorms with potentially heavy rainfall
are possible from the northern High Plains to the Upper Midwest
from Fri into the weekend as the surface front sags southward
across the central U.S. and several waves of low pressure traverse
the boundary. Showers and storms may also increase in coverage
across the central/southern Plains by Sat-Sun as the surface front
arrives in the vicinity. Scattered to numerous showers and
thunderstorms are also expected across much of the eastern U.S.,
increasing in coverage by the weekend as the cold front moves east
into the region. A cooler air mass is expected to move into the
north central U.S. in the wake of the cold front, with highs
forecast to be 5 to 15 deg F below average from Fri into the
weekend, before temperatures begin to moderate. Meanwhile, the
Northeast will initially see high temperatures 5 to 10 deg above
average Fri-Sat before decreasing to near normal values behind the
cold front by Sun.
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