Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
232 AM EDT Sun Jun 06 2021
Valid 12Z Wed Jun 09 2021 - 12Z Sun Jun 13 2021
...Locally Heavy Rainfall Next Week Across Tennessee/Ohio River
Valleys and Central Appalachians...
...Much Above Normal Temperatures Continue Across the Northern
Plains and Upper Midwest...
...Overview and Guidance Evaluation/Preferences...
Much above normal to near record warmth will continue next week
for portions of the northern Rockies/Plains and the Upper Midwest
while unsettled weather associated with a weak upper level low
could spell locally heavy rainfall across the Tennessee and Ohio
River Valleys as well as portions of the central Appalachians to
Mid-Atlantic late in the week into next weekend. Finally, a
stronger storm system approaching the West Coast is expected to
bring precipitation and unsettled weather to northern California,
Oregon, and Washington State.
The greatest model spread and uncertainty across the CONUS lies
with the progression and depth of troughing over the western U.S.
and how embedded shortwaves eject out into the northern Rockies
and northern Plains. The latest model guidance looked reasonably
clustered for this forecast cycle through much of the period,
however the 05.18Z GFS was not considered at all given its much
faster progression and evolution of the trough over the West. The
12Z run was much better aligned to the rest of the guidance as
well as both the ECENS and GEFS means. The more amplified and
slower solution is favored and this is why the faster/progressive
18Z GFS run was considered an outlier. Looking at the latest
/06.00Z/ run of the GFS, it has considerably slowed down shortwave
energy progression late next week and is in line more with the
other deterministic and ensemble guidance, so it offers some
utility in later forecasts. Elsewhere, model guidance showed
average to above average predictability with ridging persistent
across the southern to southeast U.S. while some troughing is
forecast to drop into portions of New England and the Northeast.
This will keep the northern tier and portions of the central U.S.
on the more active/unsettled weather side. The WPC blend
incorporated mostly 05.12Z model data consisting of the
ECMWF/CMC/UKMET/GFS while introducing more of the ECENS/GEFS means
late in the forecast period to account for some of the greater
spread.
...Weather Highlights/Hazards...
Locally heavy rainfall will remain possible across portions of the
Tennessee and lower Ohio River Valleys for the middle of the work
week and this unsettled weather is forecast to then spread toward
the Mid-Atlantic by late in the week as it interacts with a
backdoor cold front. Meanwhile, much above normal to near record
warmth will continue across the northern Rockies/Plains with some
periodic convective episodes as storm systems come out of the
northern Rockies. A storm system approaching the West Coast will
bring precipitation to portions of northern California, Oregon,
and Washington State late in the week into next weekend.
Taylor
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook 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