Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1204 PM EDT Mon Oct 29 2018

Valid 12Z Thu Nov 01 2018 - 12Z Mon Nov 05 2018

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

The mean synoptic pattern across the CONUS will be comprised of a
high over the West Coast with a trough over the central/eastern
states. Series of shortwaves will pass within the mean trough,
which will keep much of this region in an active wet pattern.
Deterministic and ensemble means are in agreement with the
large-scale features; however, has maintained run-to-run
variability in the timing, location and amplitude of specific
details and the degree of spread increased further in time.
Noticeable phasing arises just prior to the beginning of the
extended forecast period, Thursday morning, especially in regards
to where along the frontal boundary a wave of low pressure
develops and its evolution as it lifts to the northeast with time.

The continued approach of utilizing a multi-model blend was used
for this forecast. It was based primarily on the ECMWF/GFS/UKMET
with heavier weighting of the GEFS, NAEFS mean and ECWMF
ensembles. By days 6-7 the weighting of the deterministic guidance
was rather light. The latest guidance persisted in depicting the
shortwave energy approaching the Pacific Northwest on day 5
amplifying as it crosses the Rockies and central U.S. days 6-7.
This feature resulted in even more spread in the how the models
evolve on Sunday and Monday.


...Weather Highlights/Threats...

Potentially heavy convection may be ongoing at the beginning of
the extended period on Thu across portions of the Tennessee and
Ohio Valleys in association with the frontal wave and further
north over the Northeast in association with this frontal system
as it reaches the Eastern Seaboard. Heavy rain also be possible
across the Pacific Northwest through the weekend as upper
shortwaves/surface fronts traverse the northern periphery of the
upper ridge. These features will also bring rounds of snow to the
higher elevations of the northern and perhaps the central Rockies.
Chilly conditions will be prevalent through most of the forecast
period across much of the central U.S. beneath the persistent
upper trough, where highs will generally be 5 to 10 deg F below
average. Meanwhile, above average temperatures will persist across
portions of the West, from California into the Great Basin, where
high temperatures may reach 5 to 15 deg F above average.


Campbell


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