Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Sat Jul 04 2020
Valid 12Z Tue Jul 07 2020 - 12Z Sat Jul 11 2020
Forecast spread increases through medium range time scales a bit
more than average for this time of year. Accordingly, the WPC
medium range product suite was primarily derived from a blend of
the reasonably compatible 12 UTC Canadian, 18 UTC GEFS mean, 12
UTC ECMWF ensemble mean and the 01 UTC National Blend of Models.
Leaned blend weighting toward the GEFS mean and especially the
ECMWF ensemble mean to address growing forecast spread and to
maintain good WPC continuity. The 12 UTC Canadian was best
clustered with the ensemble means near or slightly less
progressive than a forecast envelope composite and was included in
the blend to provide added detail consistent with uncertainty. In
the East, recent ECMWF system emphasis including the newest 00 UTC
run are on the progressive side. with GFS/UKMET emphasis on the
slower side. Out West, recent GFS runs including the latest 00 UTC
GFS remain faster bringing a main upper trough to the Northwest
Thursday compared to other guidance, then amplify the flow more in
earnest downstream heading into next weekend.
...Weather Pattern/Hazard Highlights...
Unsettling Pacific upper trough energies will eventually work
inland over the Northwest next week. A steady diet of ejecting
impulses will progress downstream over southern Canada and the
U.S. northern tier. This will force a series of moderating fronts
across the region and spawn periods with strong
instability/convection and locally heavy downpours/runoff issues.
Potential may focus from the northern Rockies/Plains to the Upper
Midwest. Lead flow and mean upper ridging may bring the most
anomalous heat over the Midwest/Northeast. Elsewhere, triple digit
maximum daytime temperatures will focus from the Desert
Southwest/southern Great Basin to the south-central Plains and hot
and humid weather (including some record warm overnight
temperatures) will rule a broad expanse south of these fronts over
much of the central and eastern U.S. Some heavy convective
downpours/local runoff issues may focus into the South/Southeast
near a slow moving upper trough/closed low and wavy front.
Potential development of a slowly northward lifting coastal low
may provide an additional heavy rainfall mechanism later next week
into the Mid-Atlantic.
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at: