Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
416 PM EDT Tue Jul 02 2019
Valid 12Z Fri Jul 05 2019 - 12Z Tue Jul 09 2019
1600 UTC Update...
Minor changes were needed for the 16Z update across the CONUS with
a typical summertime pattern expected to continue through the
medium range period. Relatively progressive flow is expected for
the northern tier of the U.S. with a shortwave crossing across the
Northern Plains through Friday, then eventually through the
Eastern US this weekend. By early next week, shortwave energy
bottled up around Vancouver Island is likely to eject into the
Northern Rockies with ridging building back through the central
U.S.
A multi-model deterministic blend was used for Days 3-4 followed
by lesser weight of the 00Z CMC/UKMET for Day 5, with more
emphasis on the ECMWF/ECENS and GFS/GEFS toward the latter portion
of the forecast period. Model differences were mainly centered on
how progressive the flow becomes by Day 6-7 (Mon-Tues). The GFS
was much more progressive while the ECMWF/ECENS a bit slower with
shortwave energy coming across the northern tier. A blended
approach was favored for now and maintains a similar approach from
continuity.
Taylor/Campbell
...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
Hazards:
- Heavy rain across portions of the northern and central Plains,
Fri-Sat, Jul 5-Jul 6.
- Heavy rain across portions of the central Plains, and the
coastal area of Georgia, Tue, Jul 9.
- Heavy rain across portions of coastal North Carolina, Sun-Mon,
Jul 7-Jul 8.
- Flooding occurring or imminent across portions of the central
Plains, the middle Mississippi Valley, the lower Mississippi
Valley, the southern Plains, and the Ohio Valley.
- Flooding likely across portions of the upper Mississippi Valley
and the northern Plains.
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