Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 031159

Area Forecast Discussion
National Weather Service Norman OK
559 AM CST Sat Dec 3 2016



.AVIATION... /For the 12z TAFs/
Ceilings range from VFR in the east to IFR in the west this
morning. Gradually deteriorating conditions are expected today as
a second round of rain overspreads the area temporarily reducing
visibilities into MVFR range. Also, ceilings may fall slowly but
our current TAF forecast represents a more optimistic ceiling
forecast given the tendency for model guidance to be too low.
A better chance of IFR ceilings will arrive after sunset.
Some light fog or mist along with lingering drizzle is also
possible, especially across the south and east.


.PREV DISCUSSION... /issued 400 AM CST Sat Dec 3 2016/

Early this morning, regional radar mosaic shows widespread light
rain across most of the region. Large scale lift will be slow to
diminish today as synoptic scale changes will be slow to happen,
so high rain chances will continue. Aloft, a deep closed low was
evident in water vapor and RAP analysis over the northern Gulf of
California and was drifting slowly east. A large plume of deep
moisture was streaming northward across the area in advance of the
deep low. Weak ascent is coincident with this moisture plume
across our area.

Isentropic analysis shows persistent weak pressure advection and
very low condensation pressure deficit values. Models seem to
show some enhancement in pressure advection magnitude in the 290k
to 300k layer across the south spreading east and diminishing late
in the day. This seems to also be coincident with weak mid level
frontogenesis signal in most of the model guidance as well. For
these reasons we have confined the highest precipitation
probabilities across the south, spreading east to the southeast
portion of the area by late in the day, and then decreasing
markedly during the evening.

Deep low over Mexico will be out of phase with a faster moving
northern stream wave that will move through tonight. Deep moisture
will shift east and the rain chances will come to an end.
Lingering low level moisture may be deep enough for drizzle early
Sunday morning across roughly the southeast third of the area.
Low level winds turn northerly behind the departing northern
stream wave but there is not much change in low level thermal
characteristics upstream so colder temperatures are not expected.
In fact, without precipitation and with at least partial clearing
late in the day, temperatures should warm more than they will
tomorrow and should be very close to early December normals.

The deep closed low over Mexico will open up and accelerate across
Texas Monday bringing a period of lift to our area late Sunday
night through Monday. Rain chances have generally been confined to
the southeast two thirds of our area with the greatest chances
across the far southeast. By Tuesday, a deep/broad trough will
evolve over the western two thirds of the United States forcing a
cold front through on Wednesday. Medium range guidance still
disagrees on what part of the day the front will move through. A
period of 10-12 mb 6 hour pressure rises immediately behind the
front may support strong/gusty winds. An arctic air mass will move
in behind the front bringing the coldest temperatures so far this
season to the area for the latter half of the week.

There may be a period of light snow that is not expected to be
substantial enough for accumulation or impacts across the northern
portion of the area Wednesday just behind the advancing arctic
front. There is a better chance of moisture being deep enough and
extending to within the dendritic growth zone for snow closer to
the Kansas border, with more questionable moisture depth and
thermal profiles further south and east.



Oklahoma City OK  46  42  54  37 /  80  40  10  20
Hobart OK         45  41  54  36 /  80  30   0  20
Wichita Falls TX  47  43  55  42 /  90  30  10  30
Gage OK           43  35  53  32 /  60  30   0  10
Ponca City OK     48  40  54  35 /  60  60  10  10
Durant OK         46  43  53  43 /  90  40  20  50




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