Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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375
FXUS64 KOUN 010538
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1138 PM CST Tue Feb 28 2017

.DISCUSSION...
The 06Z aviation discussion follows....

&&

.AVIATION...
The cold front continues to sweep quickly southeast across
Oklahoma and into north Texas, while a dryline also advances east,
though not quite as fast. The cold front will have passed through
all our TAF sites by about 0900Z. Strong thunderstorms will occur
through about 0800Z over parts of south-central and southeast
Oklahoma, but should be well east/southeast of our TAF sites.
Brisk north to northwest winds will follow the cold front. A few
hours of strong winds will immediately follow the front, then a
few hours of a minor lull, then another increase in speeds by mid-
morning Wednesday as vertical mixing increases. Toward sunset,
winds will decrease rapidly, and most sites will become light and
variable by midnight tomorrow night.

CmS
&&

.PREV DISCUSSION... /issued 806 PM CST Tue Feb 28 2017/

UPDATE...
Expanded low chances for storms a bit farther west tonight, to a
Ponca City to Waurika line and points eastward. Adjusted hourly
surface elements tonight. Allowed the Wind Advisory to expire.

DISCUSSION...
A few severe thunderstorms may form and impact locations east of
a Ponca City to Waurika line between 9 pm and 3 am tonight.

Not confidence that storms will form at all in the Norman forecast
area tonight due to the strength of the low level cap. However,
based on latest HRRR model forecasts and the 18 UTC NAM12 and GFS
model runs, confidence is slowly growing that a few severe
thunderstorms may form and rapidly move east, mainly across the
eastern half of Oklahoma, tonight. The latest SPC Day 1 shifted
risk areas westward based on this guidance. Only kept rain
chances in the 20-30% range due to low confidence of occurrence.

If storms were to develop, very strong shear (0-1 km bulk shear
around 30 kt and 0-6 km bulk shear 70-80 kt based on nearby RAP13
soundings) would support a few supercells that would move quickly east
or northeast around 45 kt. First development could happen near
the line mentioned above (Ponca City to Waurika). With steep mid
level lapse rates (8-8.5C/km) and wet bulb zero heights around
9000 ft AGL, large hail would be the main concern, which could be
very large, near or larger than golf ball size. Damaging winds
would be possible if storms were to organize into a cluster or
line, but this seems very doubtful as the stronger linear forcing
should stay well north and east of Oklahoma. Even the tornado
threat would not be zero due to strong low level shear and low
LCLs due to abundant low level moisture.

Again, not sure if storms will form at all, but if they do, they
would have the potential to quickly become severe based on the
nearby environment.

The Red Flag Warning still remains in effect through 9 pm which
seems reasonable due to breezy and dry conditions in parts of
western Oklahoma and far western north Texas. Increasing humidity
values should allow this product to expire at 9 pm.

The Wind Advisory was allowed to expire at 7 pm as surface wind
gusts should remain generally below 40 mph away from any possible
storms tonight.

The cold front will continue to move south tonight, bringing
cooler and drier air along with breezy conditions.

Products will be updated shortly.

MBS

PREV DISCUSSION... /issued 610 PM CST Tue Feb 28 2017/

DISCUSSION...
The 00Z aviation discussion follows....

AVIATION...
A deep surface low near KGAG will continue to move east overnight,
dragging a cold front across Oklahoma and north Texas. Winds will
shift from south to southwest at most sites about two hours before
the front arrives, then to west, and finally northwest with the
passage of the front. It appears that any showers or thunderstorms
that occur with the front will be east of I-35, and will probably
not affect any of our TAF sites. Winds will increase for a few
hours behind the front, then subside until mid-morning Wednesday.
As daytime mixing gets going around 1500Z, winds will increase
again (from the north to northwest). Clouds should be above 12,000
ft, and no significant visibility restrictions are anticipated
through the period.

CmS

PREV DISCUSSION... /issued 237 PM CST Tue Feb 28 2017/

DISCUSSION...
Broken to overcast mid to high clouds have limited mixing for
most locations except for western Oklahoma and adjacent parts of
western north Texas. This has resulted in slightly more backed
surface winds, higher relative humidity, and cooler temperatures.
Therefore, opted to trim back part of the Red Flag Warning.

For this evening into tonight, a cold front will pass by from
northwest to southeast across the area. A tight pressure gradient
will result in gusty northwest winds for 3-4 hours immediately
behind the cold front. Some isolated storms will remain possible
in the moist sector, primarily across southeast Oklahoma. The HRRR
and HRRRX still indicate isolated thunderstorms will be possible
across southeast Oklahoma; however, greater coverage is expected
to be the east.

Northerly winds will remain breezy on Wednesday, which will
result in elevated fire weather conditions. Temperatures will be
cooler, more seasonable for late February.

By Thursday morning, the surface ridge is progged to be centered
across the Southern Plains. Consequently, many locations are
expected to be near or below freezing.

As the ridge shifts eastward, southerly winds will return across
the area late Thursday into Friday. This will commence a steady
warm-up into next weekend. Southerly winds could become quite
gusty by Saturday and Sunday. Also on Sunday, unseasonably warm
weather is expected to return across the area. Both the 28/12Z
ECMWF and GFS indicate 850 mb temperatures near 19C across western
Oklahoma.

A cold front is expected to pass by Monday, though there is some
uncertainty on the timing of the front. There will be a chance of
showers/storms as the front passes by. Cooler weather is expected
behind the front on Tuesday.

Mahale

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  41  58  31  62 /  10   0   0   0
Hobart OK         38  59  29  62 /   0   0   0   0
Wichita Falls TX  43  61  32  63 /  10   0   0   0
Gage OK           32  55  24  62 /  10   0   0   0
Ponca City OK     37  56  27  61 /  20   0   0   0
Durant OK         47  63  36  63 /  30  10   0   0

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

$$

17/23/23



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