Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1103 AM EDT Sun Jul 01 2018
Valid 12Z Wed Jul 04 2018 - 12Z Sun Jul 08 2018
...Overview and weather threats/highlights...
A closed upper high over the Northeast on Wednesday will head
westward toward the Rockies by next weekend as upper troughing
over Canada dips into New England by Saturday, bringing in cooler
temperatures (back near average). Much of the west and central
states will see an increase in warmth from Thursday onward.
Precipitation will generally focus around the upper high from the
Pacific Northwest (in conjunction with an offshore weakening upper
low) across the northern tier into the Northeast as well as on the
south side of the upper high across the Gulf Coast. By next
weekend, precipitation should precede the front southeastward into
the Mid-Atlantic and Southeast.
...Guidance evaluation/preferences...
In general, the latest model/ensemble guidance remained in
excellent agreement with the track of the upper high and good
agreement with the features around it. Given some run-to-run
shifts in timing/track of these features, a multi-model blend was
utilized for days 3-5. Model spread has increased a bit by days
6-7 with respect to how quickly the upper low off the Pacific
Northwest ejects eastward. The 00Z/06Z GFS runs have made a
significant shift from continuity, showing this energy moving
rapidly eastward, nearing Hudson Bay by Sun. Given the amplified
flow pattern, and the expected extratropical
transition/recurvature of Tropical Storm Prapiroon toward the
Aleutians by the middle of the week, would expect increased
downstream flow amplification and resultant slower motion across
the western CONUS. Thus, leaned away from the GFS by days 6-7 and
toward the slower 00Z ECMWF/CMC solutions, with increased
weighting of ensembles by next weekend. This maintained good
continuity from the previous shift.
Ryan/Fracasso
WPC medium range forecasts of 500 mb heights, surface systems,
weather grids, quantitative precipitation, and winter weather
outlook probabilities are found at:
http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4