Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1205 PM EDT Fri Jul 03 2020
Valid 12Z Mon Jul 06 2020 - 12Z Fri Jul 10 2020
1600 UTC Update...
Overall, models/ensembles continued to show relatively good
consensus at larger scales through much of the extended forecast
period, but with increasing differences at smaller scales by later
in the forecast period. Thus, no major changes were made to the
ongoing forecast with this update. The forecast was updated to
incorporate some of the latest model guidance, including the 00Z
ECMWF and 06Z GFS. A heavily deterministic blend was used during
days 3-4 (Mon-Tue), with a shift to gradually more emphasis placed
on ensemble means (00Z ECENS/06Z GEFS) through time during days
5-7 (Wed-Fri). The GFS was removed from the forecast blend after
day 5, as it became significant faster than consensus with
shortwave energy reaching the Pacific Northwest during days 6-7.
Meanwhile, the ECMWF was a bit slower than consensus, supporting
the increased emphasis on ensemble means during that time period,
which showed somewhat better consensus.
Previous Discussion (issued at 0700 UTC)...
Models and ensembles offer a reasonably similar large scale
pattern evolution, but have increasingly problematic differences
with smaller scale impulses and convection over time. This is not
uncommon for the summer. To mitigate these issues and considering
recent skill, the WPC medium range product suite was primarily
derived from a blend of the generally compatible 18 UTC GFS/GEFS
mean and the 12 UTC ECMWF/ECMWF ensemble mean along with the 01
UTC National Blend of Models. Leaned WPC blend weighting toward
the GFS and especially the ECMWF early-mid next week and then the
GEFS mean and especially the ECMWF ensemble mean mid-later next
week. This forecast strategy seems to best address growing
forecast spread and the resultant solution maintains good WPC
continuity in line with newer 00 UTC guidance.
...Weather Pattern/Hazard Highlights...
Unsettling Pacific upper trough energies will 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 south
of these fronts over the central and eastern U.S. Some heavy
convective downpours/local runoff issues may focus into the
South/Southeast/Mid-Atlantic near a slow moving mean trough aloft
and wavy/slow moving frontal drape.
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: