Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1113 AM EDT Sat Jun 30 2018
Valid 12Z Tue Jul 03 2018 - 12Z Sat Jul 07 2018
...Hot temperatures to gradually retreat westward out of the
Northeast later next week...
...15 UTC Update...
Models/ensemble remain consistent with the pattern evolution
across the CONUS through the medium range, and changes to the
forecast were relatively small in this update. A multi-model blend
including the 00Z ECMWF/UKMET/GFS was used throughout much of the
period, with modestly increased ensemble mean (00Z ECENS/NAEFS)
weighting by days 6-7. Models have trended more amplified with the
upper low off the Pacific Northwest from day 4 onward, and the
ECMWF has lagged the GFS/UKMET on this trend. Some question also
exists as to the degree of trough amplification across the
northeastern U.S. by next Fri-Sat, with the GFS continuing to be
more amplified than the ECMWF. At this time a compromise between
the highly amplified 00Z GFS and the less amplified ECMWF is
preferred.
Ryan
Previous Discussion (issued at 0607 UTC)
...Overview and weather threats/highlights...
Well above average temperatures (some record breaking) over the
eastern Great Lakes/Northeast/Mid-Atlantic early in the week will
trend westward with time as the dominant upper high (heat dome)
moves southwestward toward the Rockies by next Saturday.
Temperatures well into the 90s with lows in the 70s (near 80 in
the urban centers DC/Philly/NYC) will trend back toward near or
just above climo by next weekend. Precipitation will round the
edges of the upper high, from the Pacific Northwest to the High
Plains and along the Gulf Coast to the Southeast coast. Locally
heavy rain will be possible with organized thunderstorm
development to the north and with the weakening mid-level
circulation over the Gulf Coast early in the period (especially
Louisiana into southeastern Texas).
...Guidance evaluation/preferences...
Latest model/ensemble blend offered a good starting point -- 18Z
GFS/GEFS and 12Z ECMWF/Canadian/UKMET/ECMWF ensemble mean -- with
a majority deterministic weighting through the period with good or
better than average agreement. Around the upper high will be a few
upper lows -- off the PacNW and Southeast coast and along the Gulf
Coast -- which will spread precipitation along/downstream of their
track. Consensus timing/track differences have been relatively
small but continue to shift around with the latest trend to be
quicker through Canada and thus with the cold front into the Great
Lakes/Northeast next Thu-Sat. Off the Southeast coast, trend has
generally been for a much weaker trough, if anything, to approach
the coast late in the week.
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