Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1211 PM EDT Fri Aug 10 2018

Valid 12Z Mon Aug 13 2018 - 12Z Fri Aug 17 2018

...Pattern Overview and Guidance/Predictability Assessment...

A pair of closed mid-upper lows centered near the Central
Appalachians and Southern High Plains into early next week will
act to focus a heavy precipitation threat. Both features are
expected to gradually evolve into open waves with gradual
northeastward migration mid-later week as a potentially ampified
new trough/low digs into the north-central states/Midwest. Opted
to lean on an amplified solution given recent flow history and as
further supported by the entrainment of the extratropical
low/remnants of ex-typhoon Shanshan from the northern Pacific to
Canada. Flow amplitude on the more amplified side of the full
envelope of forecast solutions is most championed by the 00 UTC
ECMWF and GEFS/ECMWF ensembles. Over the Desert Southwest/Four
Corners region, models show a return of a warming 594-dm mid-level
ridge mid-later next week.

Accordingly, the WPC medium range product suite was primarily
derived from a composite blend of the 00 UTC ECMWF and GEFS/ECMWF
ensembles. Guidance spread and predictability seem near to
slightly better than normal.

...Weather Highlights and Hazards...

The most focused areas of heavy rainfall will linger near/ahead of
slow to eject closed lows over the Mid-Atlantic/Northeast and back
in the south-central U.S, to be followed by an upstream kicker
moving into the north-central states/Midwest. The main excessive
rainfall threat may further focus along associated/wavy fronts
that will pool depeened moisture and tap instability. Meanwhile,
decent daily chances for monsoonal thunderstorms should develop
over the Desert Southwest and the south-central Great
Basin/Rockies.

Schichtel

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