Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1143 AM EDT Thu May 30 2019
Valid 12Z Sun Jun 02 2019 - 12Z Thu Jun 06 2019
...Overview and weather highlights...
An active northern stream flow pattern is expected to continue
next week with a strong North Pacific upper-level jet splitting as
it approaches the West Coast of North America. An upper-level low
will persist in the vicinity of southern California through much
of the extended period, only very slowly moving eastward.
Meanwhile, the subtropical ridge will migrate westward and
reposition over the south central U.S. and the Gulf of Mexico.
Farther north, an upper ridge axis initially across central Canada
is forecast to slowly move east and weaken, with some potential
for ridging to become reestablished across western Canada and the
northern U.S. Rockies by the middle of next week. Downstream, a
persistent and initially fairly deep upper low across southeastern
Canada will cause incoming northern stream shortwaves to
periodically amplify as they dig into the Great Lakes and
Northeast, traversing the broader anticyclonic flow. These digging
waves along with the westward migration of the subtropical ridge
will allow for heights to fall across much of the Great Lakes/Ohio
Valley and the Mid-Atlantic/Northeast, ushering in cooler high
temperatures (near or several degrees below average) and lower dew
points through much of next week.
Relatively slow-progressing southern stream shortwaves will
periodically eject eastward from the upper low, reaching the
central U.S. and potentially interacting with amplifying northern
stream energy. These waves along with return flow across a
persistent baroclinic zone may continue to support areas of
increased convective potential from the Southern/Central Plains
into the Mid-Mississippi Valley, with the potential for at least
locally heavy rainfall/flash flooding as well as strong
thunderstorms. Predictability in location/amounts is low due to a
less-dynamic pattern overall compared to the previous two weeks.
...Guidance evaluation and preferences...
The WPC medium range product suite was initially derived from a
blend of the 06Z GFS/FV3-GFS and the 00Z ECMWF/CMC/UKMET solutions
during days 3-5 (Sun-Tue). These solutions handled features
similarly enough and any differences were favorably smoothed out
by the blend. This included some shifting of the surface low and
attendant cold front in the east Sun-Mon. By days 6-7 (Wed-Thu),
differences with upper ridging through the west favored a middle
ground solution given wavering in how long to maintain ridging
before Pacific height falls push inland. Teleconnections supported
the idea of stronger ridging but both the GEFS/ECMWF ensemble
means have trended toward allowing troughing to push east.
Fracasso/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