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

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

...Central U.S. Heavy Rainfall Threat...

...Guidance Evaluation/Preferences...

The WPC medium range product suite was primarily derived from a
blend of the latest GFS/ECMWF and GEFS/ECMWF ensemble means. These
guidance solutions have become quite well clustered compared to
yesterdays editions Wed into Sat, bolstering forecast confidence.
Increasing forecast spread portends stronger weighting on the
compatable ensemble means later Sat/Sun. However, forecast
confidence is still near/above normal as additional flow
amplification seems to make sense considering the amplified
upstream pattern over the Pacific/Alaska enhanced with entrainment
of Pacific tropical system energies.

...Pattern Overview and Weather Highlights...

In this pattern, a closed north-central Canadian upper vortex
ejects at an unusually fast pace to the Canadian Maritimes
Wed-Fri. Troughing underneath digs a cooling Canadian surface high
and lead cold fronts/precipitation across the northern half of the
central and eastern U.S. on the western and northern peripheries
of an amplified Southeast U.S. upper ridge. Ejecting
moisture/energy from the remnants of Rosa may enhance rainfall
near the front. Sufficiently cold air in place north of the
frontal boundary also supports some northern Rockies to the
northern Plains snows. In addition, ample southern stream closed
low/upper troughing moves inland over a wettened south-central
California midweek before ejecting northeastward along with a
swath of precipitation from the Southwest and south-central Great
Basin/Rockies to overtop the warming/drying Southeast U.S. ridge
Thu-Fri. The ridge holds through next weekend, bolstered building
of an unsettling/amplified western U.S. upper trough. In addition
to a renewed precipitation pattern spread over much of the West, a
downstream channel of deepening Gulf of Mexico moisture around the
periphery of the Southeast U.S. ridge will renew heavier
precipitation focus along/near the slowly moving and wavy
south-central to northeastern U.S. front/sharp baroclinic zone.
This presents a continued heavy rainfall threat and height falls
working out through the Rockies next weekend may act to
significantly invigorate Plains convection.

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