Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Mon Jul 01 2019
Valid 12Z Thu Jul 04 2019 - 12Z Mon Jul 08 2019
1600 UTC Update...
Overall minor changes were made compared to the previous forecast
cycle with the large scale pattern across the CONUS still
featuring typical summer weather. A multi-model deterministic
blend was used for the first half of the medium-range period then
a near equal blend of the 00Z ECMWF/GFS and their respective
ensemble means was used. The biggest model differences were seen
by Day 6 and 7 with respect to energy coming out of a Northwest US
trough. The 00Z ECMWF featured a more progressive flow pattern
which resulted in a stronger surface high in its wake across the
Northern Plains and Upper Midwest by Day 7. Conversely, the 00Z
GFS/GEFS (and to some degree the UKMET) showed a slower shortwave
progression with a surface low developing over the western Great
Lakes. Using a multi-model blend of the ECMWF/GFS and their
ensemble means resulted in a slight slowing trend for the northern
US surface high. Meanwhile, a cold front was adjusted further
south from the Mid-Atlantic region to the lower Ohio Valley on Day
7 (Monday).
Taylor/Rausch
...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 wavy surface front initially across the north
central U.S. is forecast to weaken before another polar front
overtakes it by later this week. An upper trough skirting the
Great Lakes/Northeast should push the cold front eastward,
eventually off the Eastern Seaboard by the weekend. Meanwhile,
another shortwave should reach the Pacific Northwest by the
weekend before moving east across the northern Rockies into early
next week.
Model solutions continued to show above average consensus at the
synoptic scale through the forecast period. Thus, a multi-model
deterministic blend (including the ECMWF/GFS/CMC/UKMET) was used
for the forecast through much of the period, and handled the
significant features during days 3-5 (Thu-Sat) reasonably well. By
days 6-7, models differed with the next shortwave reaching the
Northwest/northern Rockies, with some solutions weaker and moving
it eastward more quickly, and other showing a deeper trough
lingering farther west for longer. Thus, weight of ECENS/GEFS
ensemble means was boosted substantially in the forecast by days
6-7 (Sun-Mon).
...Weather Highlights/Threats...
Numerous showers and thunderstorms with potentially heavy rainfall
are possible from the northern High Plains to the Upper Midwest
from Thu 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 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 Thu into the
weekend, before temperatures begin to moderate. Meanwhile, the
Northeast will initially see high temperatures 5 to 10 deg above
average Thu-Sat before decreasing to near normal values behind the
cold front.
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