Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1123 AM EDT Sun Sep 30 2018

Valid 12Z Wed Oct 03 2018 - 12Z Sun Oct 07 2018

...North-central U.S. heavy rainfall threat...


...Overview and Guidance Evaluation/Preferences...

An amplified pattern will remain in place over the lower 48 (as
well as upstream/downstream from the central Pacific through to
the Atlantic) with a reloading upper trough in the west and a
resilient upper ridge in the east. The latest models/ensembles
remain in good agreement and a general blend was used as a
starting point for the forecast, which maintains good continuity
from overnight.


...Weather Highlights...

Persistent troughing in the west will be reinforced from two
sources (the northeast Pacific and western Canada) which will act
to keep cooler than average temperatures over much of the west and
into the Plains to the north of a wavy surface front. With the
upper ridge in the east/southeast anchored in place, the front
will be prevented from moving much to the southeast as waves of
low pressure (including the remnants of Rosa) lift northeastward
along a similar path from the central Plains to the Great Lakes.
This will bring rounds of rain (and some northern fringe snow) to
the same areas over several days giving way to wetter soils and
rising rivers. Temperatures to the south of the front will be
rather summer-like into the 80s and some 90s along the Gulf Coast
(5-15 degrees above average). By the coming weekend, additional
troughing into the west will nudge the trough axis eastward into
the Great Basin with more rain and high mountain snow for the
northern Rockies and a new heavy rainfall threat for the southern
Plains with mid-level southwest flow atop the lingering surface
front.

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