Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
231 PM EDT Mon Jun 07 2021
Valid 12Z Thu Jun 10 2021 - 12Z Mon Jun 14 2021
...Locally Heavy Rainfall Thursday and Friday from the
Tennessee/Ohio River Valleys to the Central Appalachians and
Mid-Atlantic...
...Much Above Normal Temperatures for the North-Central U.S Late
This Week and Weekend....
...Guidance/Predictability Evaluation...
The latest model guidance offers average to above average
predictability for the Nation during the medium range period
(Thursday-Monday) and is driven by the amplified upper level
pattern featuring a western U.S. trough with ridging across the
southern to central U.S. and some troughing becoming established
over the Northeast this weekend. The main difference from previous
WPC continuity was with placement/movement of shortwave energy
through the Rockies into southern Canada along with track of low
pressure at the surface. Much of the guidance now lifts this
energy north into south-central Canada Friday-Saturday, when
previous model runs hinted at a closed low making its way eastward
across the Great Lakes. For the 00z cycle of guidance, the only
deterministic solution still advertising this was the UKMET (and
thus it was not used in WPCs blend for today), but the new 12z
model came in better agreement with the consensus, adding some
confidence in this adjustment to continuity. The 06z GFS also
slowed down it's progression of Eastern Pacific troughing and is
now more in line with the ECMWF and the CMC with keeping the main
trough axis off the West Coast by day 7. WPC favored a blend of
the deterministic runs (ECMWF/CMC/GFS) through day 4, increasing
weighting of the ensemble means thereafter but only to a 50/50
ensemble mean/deterministic blend by day 7. Aside from what's
mentioned above, this maintained good continuity with the previous
WPC forecast.
...Weather Highlights/Hazards...
Upper level ridging building through the central U.S. will favor
much above normal temperatures from the southern High Plains into
the northern Rockies and northern Plains Thursday and then again
through the weekend to early next week (brief reprieve expected on
Friday). Departures above normal could reach 15F to 20F, locally
higher, with highs well into the 90s. These values may approach or
exceed both daytime highs and warm morning low records, especially
on Thursday and also Friday morning, for some locations.
Locally heavy rainfall capable of producing flash flooding will be
possible Thursday and Friday across portions of the Ohio Valley to
the Mid-Atlantic as moisture and lift associated with a weak upper
level feature traverses the region. Its eventual interaction with
a more substantial cold front dropping south will shunt the
moisture southward this weekend. For this upcoming weekend,
unsettled weather and higher precipitation chances will be
confined to the Southeast U.S. along the residual frontal boundary
as well as portions of the Pacific Northwest as a few waves of low
pressure move onshore.
Santorelli/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