Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1218 PM EDT Tue Jul 10 2018
Valid 12Z Fri Jul 13 2018 - 12Z Tue Jul 17 2018
...Overview, guidance evaluation and preferences...
Model guidance this evening shows good overall agreement on the
evolution of the synoptic pattern through next Tuesday. For the
500 hPa heights, pressures, and winds, used a compromise of the
00z Canadian, 00z UKMET, 00z ECMWF, and 06z GFS into Sunday
morning. Thereafter, started blending in some 00z NAEFS mean and
00z ECMWF ensemble mean to deal with the uncertainty inherent at
longer ranges. The temperatures, dew points, clouds, weather, and
precipitation chances were derived from a 50/50 mix of
deterministic and ensemble mean solutions. The preliminary days
4-7 QPF starts with a four-way blend of the 06z GFS, 00z Canadian,
00z ECMWF, and the 12z National Blend of Models. Should the 12z
GFS prove useful, its thoughts could be included as well.
...Weather highlights...
Although the dominating subtropical high will bring heat across a
large portion of the country through early next week, there will
be bouts of cool air intrusion from Canada following occasional
frontal passages across the Northern Tier. A cold front will
initially bring showers and thunderstorms across the northern
Plains into the Great Lakes Friday but as the front is forecast to
become more diffused with time, more isolated coverage in the
Northeast will be the result during the weekend. Meanwhile, the
next front will move out of Canada this weekend with scattered
showers and thunderstorms along/ahead of its boundary. Cool air
in its wake will break the heat wave across the northern Rockies
and is forecast to drop temperatures more than 10 degrees below
normal across the northern Plains early next week. Ahead of the
front, temperatures will be about 5-10 degrees above average (80s
and many 90s), and initially near or above 100 over portions of
the interior Pacific Northwest/Great Basin on Friday. But
triple-digit heat is expected to continue in parts of interior
California.
From the southeastern U.S. westward along the Gulf Coast, a
dissipating front will keep a chance of showers and thunderstorms
in the vicinity through the weekend. Monsoonal moisture will
linger across the Four Corners area where locally heavy downpours
are possible through early next week. Temperatures will generally
be near or below average in the Southwest under limited solar
insolation and a daily chance of showers/storms.
Roth/Kong/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