Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1030 AM EDT Fri Aug 03 2018

Valid 12Z Mon Aug 06 2018 - 12Z Fri Aug 10 2018

...Overview and Guidance/Uncertainty Assessment...
Pattern next week will feature a strong upper high over the
Southwest and resurgent troughing in the eastern half of the lower
48. An upper low well off the Pacific Northwest coast will only
slowly move toward British Columbia by the end of next week. There
is growing discord in the guidance suite, with the 00z Canadian
becoming quite the outlier in the central Pacific which led to
downstream problems from Wednesday onward across the
Northwest/western Canada.  The 00z UKMET appears to have issues
with frontal placement in the central Plains on Tuesday. 
Otherwise, the 06z GFS and 00z ECMWF fit their means solutions
well and are agreeable.

For the pressures, 500 hPa heights, and winds, used a compromise
of the 00z Canadian/06z GFS/00z ECMWF for Tuesday, before
switching to a blend of the 00z UKMET/00z Canadian/06z GFS/00z
ECMWF for Wednesday.  For Thursday and next Friday, used a
combination of the 06z GFS/00z ECMWF/00z NAEFS mean/00z ECMWF
ensemble mean solutions.  This led to good continuity with night
shift pressures/fronts.  The dew point, cloud, weather,
temperature, and precipitation chance grids use a more even blend
of the deterministic/ensemble mean guidance through the period. 
The days 4-5 QPF will likely be based on a blend of the 00z ECMWF,
06z GFS, 00z Canadian, 00z UKMET, and 12z National Blend of
Models.  The days 6-7 QPF will likely be composed of a blend of
the 00z ECMWF, 06z GFS, and the 12z National Blend of Models
output.  Should the 12z GFS prove useful mass field-wise, it too
could be included in the QPF preference.


...Weather Highlights/Threats...
With the upper low lingering offshore, ridging will support well
above average temperatures in the West/interior West. Random
record highs (including more numerous record warm minimums) are
again likely for the Desert Southwest, with the Great Basin
getting in on the act on Thursday.

The East will see one day of well above average temperatures on
Monday (a couple record highs and more numerous high minima
possible around NYC) before an upper trough digs/broadens across
the East and the front pushes eastward, raising the chance for
precipitation.  Precipitation will focus along/ahead of the front
that will push out of the High Plains/Great Lakes early in the
week and then into the Southeast from Wed-Fri. Warm/humid airmass
will support scattered convection with locally heavy rainfall.

Roth/Fracasso


WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes are found at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml