Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1150 AM EDT Thu Jul 12 2018
Valid 12Z Sun Jul 15 2018 - 12Z Thu Jul 19 2018
...Overview and weather highlights...
Troughing is forecast to ease into the northeast portion of the
lower 48 next week which will carry a surface front out of the
Plains and through the Mid-Atlantic states. Temperatures will be
near to above average (anomalies about +5 to +15F) ahead of this
boundary with some isolated record highs possible in an otherwise
typically hot summertime regime. The cold front will bring in
drier and slightly cooler air in its wake (anomalies about -5 to
-10F), first to the High Plains late this weekend then to the
Midwest and Northeast later in the week. Precipitation will follow
along the path of the front with scattered showers/storms over the
Southeast and interior west with a decrease in time over the Four
Corners region as upper ridging strengthens.
...Guidance evaluation and preferences...
Models/ensembles show good agreement overall with much of the
timing differences confined to the higher latitudes north of the
US/Canadian border. However, run-to-run consistency remains a bit
lackluster and confidence in the details after Tuesday next week
were average at best. Problems stem from short range uncertainty
over Alaska that carries into Western Canada early in the period
that set the stage for the troughing in the east Tue-Thu. Recent
00Z/06Z GEFS ensembles and ECMWF ensembles have somewhat converged
over the Midwest/Great Lakes by next Wed/Thu (at least compared to
the 12Z runs from yesterday) so a blend among the deterministic
GFS/ECMWF and their ensemble means was usable through the period.
This resulted in a quicker frontal progression through Canada and
the east Tue-Thu but otherwise maintained continuity.
Fracasso
WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes 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
http://www.wpc.ncep.noaa.gov/heat_index.shtml