Area Forecast Discussion
Issued by NWS Tulsa, OK

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FXUS64 KTSA 091118

Area Forecast Discussion
National Weather Service Tulsa OK
518 AM CST Fri Dec 9 2016

VFR conditions will prevail at all sites through the TAF period.


.PREV DISCUSSION... /Issued 300 AM CST Fri Dec 9 2016/


The main forecast challenge thru the first week of the forecast
will be temperatures, as we oscillate in and out of arctic air

Highly amplified flow in the high latitudes has opened the door
for arctic cold to grip a good portion of the nation. To the south
over the CONUS, a strong near zonal upper jet dissects the nation.
A strong upper jet streak will migrate east off the Atlantic
coast thru tonight, while another jet streak located off the
Pacific coast moves inland. Increasing downslope flow over the
Rockpile will induce lee troughing and a return to southerly winds
while the arctic high center slides east toward the Mid Atlantic
this upcoming weekend. The result will be a gradual exit of the
arctic cold initially, followed by a rather rapid change in
airmass by Sunday as the upper jet streak/shortwave trough moves
into the Plains.

Low level moisture will increase enough on Sunday to support
drizzle and even some scattered showers mainly over far Eastern OK
and Western AR going into Sunday evening. So, after seeing highs
in the 30s yesterday, highs are likely to climb into the 60s on
Sunday across portions of the area. With the upper wave and
associated surface low passing by to our north, there will not be
any winter weather potential with this system, as the lift/precip
will be ahead of the cold front as it sweeps thru Sunday night.

The Sunday night front will be of Pacific origin, so while temps
will be cooler Monday than the abnormally warm day expected Sunday,
most places should see 50s for highs.

Now we switch gears and focus on the next arctic intrusion
expected to arrive in our area by the middle of next week. This
next intrusion into the CONUS will be even colder than the current
one, and likely something we haven`t seen since at least the
2014-2015 winter season. Currently there is an upper high over the
Arctic Ocean north of Alaska. A strong upper jet extends from
Siberia across the North Pole /i.e. cross-polar flow/ and is
headed south toward the Northwest Territories. This jet will
continue to dive south toward Western Canada next week. Meanwhile,
the Polar Vortex over Baffin Bay is expected to merge with this
jet energy and migrate south toward Central Canada, setting up
over Manitoba and Ontario by midweek. As a result, a slug of sub
-20C 850mb temp air will come south and grip much of the North
Central CONUS, gripping this part of the country with dangerously
cold air. The leading edge of this arctic air will begin to arrive
in our part of the country on Tuesday and will truly be felt
Tuesday night and Wednesday. Highs on Wednesday probably will
struggle to reach freezing north of I-40. It is not out of the
question that we could see some light freezing drizzle or snow on
Wednesday behind the arctic front, but indications are that this
will not be significant, as a general NW flow aloft will not
provide significant lift over the cold air. It appears this arctic
intrusion will be brief as well, with strong southerly flow in
place by Friday.

As we look ahead into the 7 to 10 day time frame, the GFS and
ECMWF look eerily similar in the overall large scale pattern, with
a huge positive tilt upper trough developing over the Western
CONUS and a storm track right overhead. It`s certainly not out of
the question we could see our first significant winter weather of
the season in week 2.





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