Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Aug 30 2018

Valid 12Z Sun Sep 02 2018 - 12Z Thu Sep 06 2018

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

A series of shortwaves aloft will progress over southern Canada
and the U.S. northern tier states overtop both an emerging
southern stream energy underneath into a developing trough over
the West and a sprawling late summer ridge centered over the
mid-latitudes of the central and eastern U.S. The large scale
pattern is reasonably depicted in guidance as impulses and
deepened moisture emerge from the southwest and northwest to
interact and track around the western periphery and overtop the
aforementioned hot ridge. However, models and ensembles are quite
uncertain with the timing/amplitude/interaction of these
convection driving small-moderate scale embedded weather features.
Within the subtropics, several tropical waves/disturbances are
slated to move westward across the Florida Peninsula and the
northern Gulf of Mexico/Gulf Coastal areas.

Given lingering uncertainty, the WPC medium range product suite
was primarily derived from a composite blend of the 12 UTC
GEFS/ECMWF ensembles, the NBM and WPC continuity.


...Weather Highlights/Hazards...

Specifics are uncertain, but there are several strong signals
supporting a larger scale hazard that wavy/slow moving frontal
systems will combine with theta-e advection/pooled moisture and
instability to fuel periods of heavy convection/MCS activity. The
most organized threat should focus across the central Plains and
mid/upper Mississippi Valley into the Great Lakes. Meanwhile,
Pacific energies working inland in separated southern stream flow
are expected to renew some monsoonal connections/convection for
the Southwest and South-central Great Basin/Rockies in a bout of
later summer activity. Also, the passage of potential tropical
waves/disturbances will set the stage for clusterd heavy rainfall
over Fl and the Gulf Coast.

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