Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
124 AM EDT Wed Jul 03 2019
Valid 12Z Sat Jul 06 2019 - 12Z Wed Jul 10 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 mean upper trough in
the vicinity of Hudson Bay. An upper trough skirting the Great
Lakes/Northeast Sat-Sun is expected to push a cold front southward
through the central U.S. and eastward across the Ohio Valley to
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 before it begins to lift back
northward as a warm front ahead of the next system. 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 by the early to
middle portion of next week as it weakens.
A multi-model blend including the ECMWF/GFS/UKMET/CMC was used as
a forecast starting point during days 3-5 (Sat-Mon). These
solutions handled the shortwave and cold front crossing the
central/eastern U.S. during that time frame similarly. Models
begin to show some differences surrounding the western trough
starting on day 5, which grow substantially through the day 6-7
(Tue-Wed) time period. In general, models/ensembles have trended
toward a slower eastward progression of this system, keeping lower
heights in place across the western U.S. for longer. The GFS has
consistently moved this energy eastward much quicker than
consensus for the past several runs (an idea that is not supported
by the GEFS mean), whereas the ECMWF has slowed the system down in
line with the general trend and the ECENS/GEFS means. Thus, the
forecast during days 6-7 was based on a blend of majority
ECENS/GEFS ensemble means along with some continued use of the
deterministic ECMWF (about 1/3) through the end of the forecast
period.
...Weather Highlights/Threats...
The frontal boundary crossing the central/eastern U.S. through
much of the forecast period will focus areas of scattered to
numerous showers and thunderstorms across a large area, including
portions of the Plains, Ohio/Tennessee Valleys, and the Eastern
Seaboard through the middle of next week. Models show a signal for
areas of heavy rainfall along the immediate Southeast U.S.
coastline from Sun into the middle of next week. A renewed threat
of more widespread convection may develop across the Northern
Plains and Upper Midwest by Mon-Tue as the next surface front and
surface low move into the region ahead of the shortwave energy
crossing the northern Rockies. High temperatures are expected to
be 5 to 10 deg F above average across the Northeast on Sat ahead
of the incoming cold front, but temperatures should decrease in
the wake of the front to near seasonal norms starting on Sun.
Meanwhile, a brief period below average temperatures is possible
across the northern High Plains behind the front on Sat, before a
return closer to normal on Sun. Finally, an area of relatively
coo. temperatures (highs 5 to 10 deg below average) may accompany
the upper trough across the Northwest/Great Basin/northern Rockies
during the early to middle portion of next week.
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