Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 211734
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1134 AM CST Sat Jan 21 2017

.DISCUSSION...


&&

.AVIATION...
Ceilings will gradually lower through the evening while a low
pressure system moves west to east across southern Oklahoma. Areas
of light rain are expected through the evening. Gusty southwest
winds may develop over southwest Oklahoma this afternoon before
becoming gusty from the north when the low pressure passes
tonight.

&&

.PREV DISCUSSION... /issued 1007 AM CST Sat Jan 21 2017/

DISCUSSION...
A few showers/storms have formed over the past hour or so
just south of Wichita Falls. Reflectivity values
around -10C have exceeded 40 dBz at times which fits
well with several lightning strikes across Archer
county.  A little difficult to tell how far east
these showers/storms may survive, but mid-level lapse
rates over north Texas and south central Oklahoma
are more supportive than the area farther north.
After this morning, may see a slight decrease in
radar returns but that will certainly change by mid to late
afternoon as an upper low quickly approaches. May adjust pops
higher over south central Oklahoma for this morning/early
afternoon otherwise, no main changes.

PREV DISCUSSION... /issued 546 AM CST Sat Jan 21 2017/

DISCUSSION...

AVIATION... /For the 12z TAFs/
VFR conditions are expected through mid afternoon before
probabilities of MVFR to possibly IFR visibilities and ceilings
develop. Rain showers are expected to develop later this afternoon
and be most numerous from Interstate 40 north. Timing of
prevailing -RA/-SHRA in the latest TAFs indicates our best guess
for window when precipitation and possible visibility and ceiling
decreases are most likely. Some adjustment may be needed.
Restrictive ceilings may occur after the precipitation ends
through the end of the TAF period.

PREV DISCUSSION... /issued 408 AM CST Sat Jan 21 2017/

DISCUSSION...
Only minor adjustments were needed to the previous forecast based
on the latest suite of model guidance. Weather impacts should be
limited through the forecast period with perhaps the greatest
concern being elevated to near critical fire weather conditions
this afternoon and again on Tuesday afternoon (see Fire Weather
section below).

The upper flow pattern across the country remains progressive but
fairly amplified with relatively short wavelengths between
troughs. One shortwave trough clearly evident in water vapor over
northwest Missouri early this morning is moving away from the
area. Our attention shifts westward to an intense 125+ knot 500 mb
jet near coastal California, and will dig/deepen into a closed low
over the Texas Panhandle by this evening. Ageostrophic response
will yield a period of ascent across the area today, first at
high levels resulting in thickening cirrus. This can already be
seen in satellite imagery to our west early this morning. By
afternoon, a band of deeper moisture ahead of an eastward
advancing Pacific cold front/occlusion should result in some
showers moving across the area into early-mid evening. This is
round one of greatest precipitation chances.

Some of the same features we would be looking at for a classic
snow event are present with this system given the character of the
upper trough/closed low. Fortunately (at least from a weather
impacts standpoint) temperatures are too warm for wintry
precipitation. A warm conveyer on the north side of the closed low
and deformation area should result in light rain showers across
mainly northern sections of the area into the night. This is the
second of two fairly distinct periods of precipitation. Light rain
showers could linger in the eastern portion of the area through
Sunday morning.

One final aspect of this system worth mentioning is the potential
for near advisory criteria wind across the extreme southwestern
portion of the area (specifically around Crowell, Benjamin, and
Seymour). If deeper mixing is able to occur later today, we may
need to raise forecast wind speeds slightly. We will monitor
observational trends and update as necessary.

This system is separated from cold arctic air mass to the north
so a surge of cold temperatures is not expected as it departs. In
fact, temperatures may still be slightly higher than mid-late
January normals on Sunday. Warmer temperatures are expected Monday
as mean ridging is present over the area. Our confidence in the
forecast into the middle of next week is quite high since medium
range deterministic and ensemble spread is fairly low. Model
guidance indicate a positively tilted longwave trough developing
over the western half of the country with a lead shortwave forcing
a fairly substantial surface cyclone that will pass to our north
on Tuesday. As this happens, surface winds will veer and
strengthen and a windy day is expected. Conceptually, this pattern
fits some of our windier days. As it appears right now sustained
speeds around 30 mph (with gusts 40-45 mph) certainly seem
possible across western portions of the area, tapering off to
around 20 to 25 mph further east into central Oklahoma as is
typically the case. We will need to watch this carefully,
specifically any mid-high clouds that could limit mixing, and
timing of an intense mid-level speed max. If everything lines up
right, higher winds than the above first guess will be possible.

Medium range guidance generally agrees on a cooler pattern
Wednesday into Thursday behind a cold front. This system will be
more likely to tap modified arctic air leading to below normal
temperatures Wednesday and Thursday before some modification
occurs Friday. No precipitation is expected next week.

BRB

FIRE WEATHER...
Low end fire weather concerns will arise later this afternoon
across portions of western north Texas and possibly far southwest
Oklahoma. Peak temperatures in the upper 60s to near 70 are
expected. 20 foot winds will reach or exceed 20 mph, but the
driest air mass behind eastward advancing Pacific cold front is
not expected until after peak heating and lowest RH values occur.
Nevertheless, RH will drop to around 30 to 35 percent across this
area during the warmest part of the day. Latest ERC values are
around or just under 30. If any fires persist into the night, fire
managers need to be aware of gradually veering winds to
northwesterly overnight and breezy conditions persisting into
Sunday morning.

Meteorological conditions will reach elevated to possibly near
critical across a larger portion of the area Sunday afternoon,
albeit to a lesser magnitude. Limiting factors for a more
significant fire weather episode will be 1.) cooler temperatures
as northwesterly flow behind departing shortwave trough ushers in
slightly cooler air, 2.) lower wind speeds than the previous day,
and 3.) an RH drop to a minimum of 30 to 35 percent.

The most concerning day with regards to fire weather potential is
Tuesday. Although some uncertainty remains and a shift in mid-
level speed max, higher amount of mid-high clouds tempering how
deep we mix, and/or shift in position of thermal trough could
occur, meteorological conditions will probably reach near critical
to critical. Furthermore, conceptually this pattern is typically
conducive to active fire days with a pronounced low level thermal
ridge juxtaposed with strong mid-level speed max.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  65  42  57  33 /  20  60  30   0
Hobart OK         65  40  59  32 /  40  30   0   0
Wichita Falls TX  69  42  62  35 /  40  20  10   0
Gage OK           61  37  56  28 /  50  60   0   0
Ponca City OK     62  42  55  29 /  20  70  30   0
Durant OK         69  45  60  38 /  30  40  20   0

&&

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

$$

06/09/09


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