Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1108 AM EST Mon Nov 12 2018

Valid 12Z Thu Nov 15 2018 - 12Z Mon Nov 19 2018

...Overview and Guidance/Uncertainty Assessment...

Models continue to agree on the overall pattern: the upper ridge
strengthening over the West Coast with a downstream mean trough
settling over the eastern U.S. The details in both of these
features diverge with the different solutions.

In the beginning of the medium range period, a closed upper low
over the lower Mississippi Valley/Tennessee Valley will lift
northward toward the Mid-Atlantic on Thursday and into Friday. The
06Z GFS is slightly faster with the progression of this closed low
as compared with the 00Z ECMWF. Meanwhile, the 00Z CMC agrees with
the slower solution.  The 00Z UKMet was much faster and farther
north with this low--thus, it was completely discounted. At the
surface, the 06Z GFS was faster with the front as a result but
both the GFS/ECMWF were still within a reasonable range of each
other. In the northern tier states/Great Lakes, the 06Z GFS/00Z
ECMWF are in agreement on the overall timing with the energy
skirting across the Great Lakes. By the weekend, shortwave energy
will slide down the upper ridge on the West Coast which will lead
to a more rounded eastern mean trough. The details begin to become
apparently different by the weekend.

Out west, the upper level ridge will begin to build across the
West Coast.  In the Pacific, a trough will begin to dig farther
south and eventually split to become a closed low. This will lead
to the ridge breaking down by the end of the weekend and into
early next week. Once again, the 06Z GFS and the 06Z GEFS mean
were more progressive with the low in the Pacific and faster with
pushing the ridge inland while breaking down. The 06Z GEFS mean
also continued to show more separation with the closed low than
the 00Z ECENS mean. The operational models and their means all
agree that the ridge weakens as it centers over the Central Great
Basin while the closed low approaches the West Coast.

WPC ended up using a blend of the 06Z GFS/00Z ECMWF throughout the
medium range forecast due to their overall agreement with the
pattern.  Increased the usage of their respective means by the
weekend and into Monday to help with the differences in detail.


...Weather Highlights/Threats...

As the occluded system begins to lift out of the Southeast and
move into the Mid-Atlantic, precipitation of various types will be
impacting these regions.  In the Southeast and Mid-Atlantic, heavy
rainfall could be a concern on Thursday and Friday--with wintry
precipitation in the higher elevations of the central Appalachians
and the interior of New England. With the system moving into the
Great Lakes late this week, light precipitation can be expected. 
However, with cyclonic low level flow due to the mean trough
setting up over the eastern U.S., some lake effect snow can be
expected. As the shortwave drops into the northern tier states
early into the weekend, there is a possibility of snow across the
northern Rockies/High Plains on Friday and into Saturday. There
could be light precipitation on Thursday and into Friday for the
Pacific Northwest, however the West Coast will stay dry for the
rest of the medium range period.

Temperatures will be quite cool for the central and eastern U.S.
by the weekend and through Monday.  High temperature anomalies
will be 12-16 degrees below normal. The western U.S. can expect
high temperatures to be 5 to 15 degrees above normal.


Reinhart


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