Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
420 PM EDT Wed Jul 03 2019
Valid 12Z Sat Jul 06 2019 - 12Z Wed Jul 10 2019
...Overview and Guidance/Predictability Assessment...
Moderately progressive flows will channel between a building/hot
upper ridge over the U.S. southern tier and a mean upper trough
near Hudson Bay. A series of convection focusing impulses/troughs
will work over the U.S. northern tier. This will act to push a
cold front southward over central and eastern U.S. This main front
will provide stark contrast between refreshing post-frontal high
pressure and an anomalously hot and humid warm sector. 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. Southern stream impulses rotating around and
lingering into the ridge will also provide a less certain local
focus for convection/MCS activity into the hot sector. 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 to 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), transitioning
increasingly to ensemble means days 6/7 amid growing forecast
spread and run to run continuity variance.
...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
cool 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/Schichtel
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 Upper Mississippi Valley and
the Northern Plains, Mon-Wed, Jul 8-Jul 10.
- Heavy rain across portions of the Southeast and the
Mid-Atlantic, Sat-Tue, Jul 6-Jul 9.
- Flooding occurring or imminent across portions of the Central
Plains, the Middle Mississippi Valley, the Lower Mississippi
Valley, and the Ohio Valley.
- Flooding likely across portions of the Upper Mississippi Valley
and the Northern Plains.
- Excessive heat across portions of the Lower Mississippi Valley,
Mon-Wed, Jul 8-Jul 10.
- Enhanced wildfire risk across portions of the mainland Alaska,
Sat-Wed, Jul 6-Jul 10.
- Enhanced wildfire risk across portions of the the Alaska
Panhandle, Sat-Sun, Jul 6-Jul 7.
- Much above normal temperatures across portions of mainland
Alaska, Sat-Wed, Jul 6-Jul 10.
- Much above normal temperatures across portions of the Alaska
Panhandle, Sat-Sun, Jul 6-Jul 7.
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