Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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000
FXUS64 KOUN 150458
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1058 PM CST Thu Dec 14 2017

.AVIATION...
VFR conditions continue. Mid clouds continue to gradually
dissipate as they move south and east through the southern Plains.
Most sites will have clear skies before sunrise. Light
north/northwest winds will become southwesterly by Friday
afternoon. Wind speeds may increase toward end of forecast period
as pres gradient tightens.

&&

.PREV DISCUSSION... /issued 844 PM CST Thu Dec 14 2017/

DISCUSSION...
Clouds across western and northern Oklahoma will continue
to move south and slowly dissipate this evening and overnight.
A mid-level trough will move quickly across the area with a weak
surface reflection of slightly stronger surface winds. Drier air
will filter into northern and western Oklahoma overnight where
colder overnight lows are expected.

Overall, the forecast looks reasonable and little if any changes
are expected.

PREV DISCUSSION... /issued 538 PM CST Thu Dec 14 2017/

AVIATION...
VFR conditions to continue. There will be a band of mid-clouds
that will translate north to south across the area overnight. Light
north winds will shift to the west and southwest late in the
period.

PREV DISCUSSION... /issued 254 PM CST Thu Dec 14 2017/

DISCUSSION...
No significant changes were made to the previous forecast. Low-end
fire concerns remain for Saturday, with some potential limiting
factors (see fire weather section below). The only precipitation
chance is Saturday night across roughly the eastern two-thirds of
the area. Mild temperatures that shouldn`t be too far above mid-
December normals are expected for the rest of the forecast period
with increasing confidence in a colder pattern by late next week.

A weak frontogenesis precipitation band (mostly virga) set up east-
west across portions of the High Plains into far northwest Oklahoma
this morning. No observations of rain or snow were received in our
area, and it`s doubtful that much if anything reached the ground in
northwest Oklahoma given the high cloud bases and dry sub-cloud
layer. Further west, in southwest Kansas some light snow was
observed.

An upper low at the base of an elongated positively tilted trough
will continue to deepen through tomorrow in the Gulf of California
region. This low will open and eject northeastward into our area
Saturday in response to digging/deepening trough in the west. Modest
moisture return and forcing for ascent should be enough for light
rain across much of eastern Oklahoma and portions of central and
southern Oklahoma Saturday night.

There is still considerable spread in deterministic models and GFS
ensemble members in timing and characteristics of western trough as
it lifts out. There are a couple scenarios that could favor another
low-end light precipitation event at some point early next week, but
confidence is low and kept the forecast dry for now. Several of the
ensemble members suggest a more open/progressive system that would
probably yield no precipitation. If something along the lines of the
more closed off/deeper GFS deterministic were to happen, we may need
to add a period of light precipitation. The ECMWF is more open, but
slower and closes off a mid-level low by early Tuesday. It`s the
slow outlier. Again, dry for now, and we`ll watch trends and wait
for converging medium-range solutions.

A period of zonal flow and mild to above average temperatures is
expected mid-week. A deep western trough looks to force a strong
cold front south through the area bringing a colder pattern by late
week. This is the general pattern shown in medium range guidance but
details on magnitude and timing of the cold surge is yet to be
determined. The way the pattern looks to evolve beyond the
forecast period, there could be some hope for meaningful
precipitation during the latter half of the weekend of the 23rd-
24th or around Christmas, but it`s too early to have any
confidence in this yet.

BRB

FIRE WEATHER...
Fire weather concerns are minimal until Saturday. On Friday, deep
mixing across our western north Texas counties will probably
result in significant drops in relative humidity during the
afternoon, but the period of lowest RH should be coincident with
when surface ridge axis moves over resulting in light winds.

Saturday holds some potential for at least low-end fire activity,
especially when considering the fuel environment. Meteorological
conditions may be marginal for very much concern, but fuels are
dormant and a prolonged dry period has brought ERC-G values to near
daily maximum and at/near the 90th percentile for the fire season.
One potential caveat is thick cirrus limiting fuel heating and
tempering depth of mixing Saturday afternoon. Models suggest a
rather robust surge of high level moisture throughout the day
ahead of ejecting shortwave trough. Nevertheless, the lower-mid
troposphere is very dry and even slightly deeper mixing than
currently forecasted suggests potential for lower relative
humidity values than currently forecast.

Considerable uncertainty exists toward middle/late next week given
the spread in medium range model guidance. There may be some
increased fire weather concerns by Wednesday as low-level flow veers
to west/southwesterly (downslope) and surface winds increase ahead
of another deepening trough in the west. We`ll monitor the mid-week
timeframe closely and assess model trends for potential elevated or
greater fire weather concerns.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  29  52  33  60 /   0   0   0   0
Hobart OK         26  54  30  60 /   0   0   0   0
Wichita Falls TX  30  54  31  62 /   0   0   0  10
Gage OK           22  57  30  64 /   0   0   0   0
Ponca City OK     27  52  33  60 /   0   0   0   0
Durant OK         32  54  32  59 /   0   0   0  10

&&

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

$$

06/30/01



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