Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 AM EDT Sun Jul 08 2018
Valid 12Z Wed Jul 11 2018 - 12Z Sun Jul 15 2018
...Pattern overview/Guidance evaluation/Preferences...
Model guidance this evening is in excellent agreement on the
general evolution of the synoptic pattern across North America
through next weekend. An upper-level trough moving into the
Northeast early in the week is forecast to lift toward
southeastern Canada by midweek. This will bring a cold front
through the Northeast into much of the Mid-Atlantic and help
accelerate what is still Tropical Depression Three off the North
Carolina coast toward the northeast. The UKMET has been
advertising the storm to linger a bit longer off the Southeast
U.S. coast before accelerating it just off or across coastal New
England around the Day 4-5 time frame. This scenario has been
discounted. Consult NHC products for latest information on T.D.
Three.
As the upper trough lifts out of the Northeast, models are in
unanimous agreement that the warm subtropical high will
reestablish and anchor itself over the central Plains with a
slight tendency of extending a ridge westward into the western
U.S. through next weekend. Meanwhile, a couple of shortwave
troughs are indicated to traverse western Canada just north of the
U.S.-Canadian border. Despite their relatively fast zonal
movement, models are in excellent agreement on their speeds of
motion and amplitudes. The associated cold fronts will likely
move across the northern tier states through the medium-range
period.
Therefore, the evening WPC medium-range grid package was a
consensus of the 12Z and 18Z GFS together with the 12Z ECMWF with
more of the 12Z GEFS mean and 12Z EC ensemble mean included toward
Days 6 and 7. The 12Z GEFS was chosen instead of the 18Z GEFS due
to better agreement with the 00Z EC mean on the surface features
in central Canada. Their U.S. surface features are in excellent
agreement however.
...Weather threats/highlights...
With the subtropical high forecast to reestablish over the central
U.S., temperatures are expected to remain above average across the
region through next weekend. Farther north across the northern
tier into the Northeast and Mid-Atlantic, periodic cold frontal
passages will bring occasional breaks in the heat and humidity
along with passing showers and thunderstorms. South of the center
of the subtropical high, an active monsoonal flow regime should
keep temperatures below normal with showers and thunderstorms
likely across the Four Corners region. Over the western U.S.,
expect well above normal readings to persist across the interior
Pacific Northwest throughout the end of the week with triple-digit
heat most likely on Thursday. Meanwhile, a good chance of showers
and thunderstorms can be expected to persist across the southeast
U.S., Florida and along the Gulf Coast through this week, keeping
temperatures near or slightly cooler than normal.
Kong
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