Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
203 AM EDT Fri Jun 28 2019
Valid 12Z Mon Jul 01 2019 - 12Z Fri Jul 05 2019
...Overview and Guidance/Predictability Assessment...
Relatively progressive northern stream flow will be squeezed in
between a building ridge across the southern half of the CONUS,
and more strongly blocked flow at higher latitudes, from the North
Pacific across Canada. This will keep an active upper jet in place
from the Pacific Northwest to the Midwest, Great Lakes, and
Northeast through the medium range. A surface front will persist
from the northern/central Plains to the Great Lakes through the
forecast period along the northern periphery of the upper ridge,
reinforced by another polar front by the middle of next week. A
broad weakness in the upper ridge is expected to initially be in
place across the southern Plains, with little in the way of
movement until perhaps a stronger shortwave traverses the northern
Plains/Midwest by late next week.
Model consensus was sufficient through much of the forecast period
to employ a multi-model blend of deterministic guidance
(ECMWF/GFS/UKMET/CMC) as a basis for the WPC forecast. The largest
differences among the guidance occurred by days 6-7 (Thu-Fri) with
respect to a rather complex series of shortwaves diving south
through western Canada and into the Pacific Northwest before
ejecting east toward the northern Plains. Models showed
significant differences on both timing and amplitude of these
features, as well as with any potential interactions with the
broader upper low near Hudson Bay and the aforementioned upper
weakness across the central U.S. Given increased spread, the
forecast by days 6-7 was shifted heavily toward a blend of
ECENS/GEFS ensemble means, given the overall agreement of the
means at larger scales.
...Weather Highlights/Threats...
The persistent surface front extending from the north central U.S.
to the Great Lakes will serve to focus areas of showers and
thunderstorms across multiple days, with locally heavy rainfall
possible. Showers and storms could spread east across portions of
the Appalachians and Mid-Atlantic regions by the middle to end of
next week. Farther south, the upper weakness will also focus
scattered showers and thunderstorms across portions the
southern/central Plains, especially by the middle to latter
portion of next week as moisture inflow from the Gulf of Mexico
increases. Meanwhile, high temperatures of 5 to 10 deg F above
average across the Southeast and southern Mid-Atlantic through
much of the forecast period will combine with a relatively humid
air mass to produce potentially dangerous heat index values over
100 degrees.
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