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Prognostic Meteorological Discussion (PMD)

Issued by National Weather Service (NWS)

                            
000
FXUS02 KWBC 191607
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1106 AM EST Mon Nov 19 2018

Valid 12Z Thu Nov 22 2018 - 12Z Mon Nov 26 2018

...Record cold temperatures on Thanksgiving/Black Friday for much
of the Northeast/New England...

...Could be the coldest Thanksgiving since 1996 for the
DC-PHL-NYC-BOS corridor...


...Overview...

Very cold but mostly dry in much of the east while it will be
stormy in the western US later this week. A couple of cold fronts
will push across the lower 48 and potentially lift up along the
East Coast Sat/Sun during a very busy travel time. Above average
temperatures in the High Plains will trend back to below average
by next week.


...Guidance/Uncertainty Assessment...

Model guidance suggest a split flow pattern through much of
extended periods, with the southern stream becoming more dominant
this weekend. Model differences are apparent after day 3
(Thanksgiving) and continue to increase through the end of the
forecast. The last two runs of the GFS continue to be faster while
the ECWMF, Canadian, UKMET and ensemble means maintain a
slower/west solution. Chose to maintain continuity by using a
multi-model blend, using the GFS very sparingly.

Guidance continues to depict a pair of fronts converging/slowing
over the mid-Mississippi and western Ohio Valleys as the upper
trough sharpens. This may take another area of low pressure
northeastward but on the west side of the Appalachians next
Sun/Mon. Again preferred the slower/sharper solutions unlike the
recent quicker/weaker GFS runs.


...Weather Highlights/Threats...

A rather chilly Thanksgiving Day is in store for much of the
Northeast, lower Great Lakes and northern Mid-Atlantic regions
where afternoon highs will hover near 15 to 30 deg F below
average. The majority of area will stay well below freezing, while
low temperatures may reach the single digits on either side of
zero. The much below average temperatures in the Northeast will
slowly ease back toward typical late November values by the
weekend (and likely above average minimum temperatures).

The entire West Coast and much of the interior West will be in a
prolonged active, wet pattern. With extensive cloud cover
expected, overnight temperatures are forecast to be near or above
average through the extended periods. Widespread rain/elevation
snow will likely result in multi-day totals of 3-6 inches,
especially over the favored upslope areas- even about an inch to
an inch and a half in the Central Valley. Snow levels will waver
but generally fall through the period with several feet of snow
likely at the highest elevations. Across the High Plains, this
next week will generally be mild and dry with temperatures mainly
in the 40s and 50s, cooling to the 30s and 40s during the weekend.
The cooler temperatures will reach the Central Plains/Midwest by
the weekend as a cold front passes through.

The Gulf Coast has an increasing chance for rain as a low pressure
system develops and tracks east across the South and Southeast,
which may support the potential for heavy precipitation across
portions of the Southeast, Mid-Atlantic, and southern/central
Appalachians as the system transitions to a Nor'ester. This may
coincide with another very busy travel day on Sunday.


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

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