Winter Storm in Oklahoma, December 27, 2018

Area Forecast Discussion
National Weather Service Amarillo TX
1021 PM CST Wed Dec 26 2018

.AVIATION...06Z TAFS...
Conditions will continue to deteriorate at KDHT and KGUY as a
rain/snow band will set up from southwest to northeast for the
first 6 to 12 hours of the TAF period. Accumulating snow will be
possible at these sites, mainly after 09Z. Expect IFR to VLIFR
conditions to occur during these periods. Winds will be in the 20
to 30kt range out of the northwest for the first 6 to 12 hours,
and blowing snow is anticipated at KDHT and KGUY.  After 12-15Z
conditions should improve and mostly VFR is expected for the
remainder of the TAF period. KAMA will be mostly VFR with possible
MVFR/IFR lowered cigs, but it doesn't look long lived, mainly in
the 08Z-11Z time frame. The rain/snow band is expected to stay
northwest of KAMA, so no precipitation is forecast at this time
for the TAF period.

Weber

&&

.PREV DISCUSSION... /Issued 926 PM CST Wed Dec 26 2018/

UPDATE...
Although deterministic models are coming in a tad warmer
overnight tonight, the threat still remains for possible snow
bands. The low continues deepen and the deformation zone now looks
to cover a little more of the northwest Panhandles, thus the
expansion of the Winter Weather Advisory. New counties that have
been added are Sherman and Hartley. Right now only looks like an
inch or two, for these areas, but depending on how fast the
precipitation changeover occurs could greatly impact these
numbers, as well as the other counties already in the Advisory.
Kept Moore and Hansford Counties out for now, but wouldn't rule
out an inch in the northern Part of Moore County and northwest
Hansford County. But area coverage suggests most of the counties
will only see about a half an inch or less. Winds still look to be
gusting in the 45 mph range across much of the northwest
Panhandles, and blowing snow with reduced visibilities still
remains a concern. There is the potential for 6 to 18 inch snow
drifts in the Advisory area.

Everything is very much contingent on where the banding sets up,
therefore the slightest shift in the banding could warrant added
Advisories, or upgrades to warnings depending on snowfall rates.
Continue to monitor the forecast and check back for updates.

Weber

PREV DISCUSSION... /Issued 259 PM CST Wed Dec 26 2018/

DISCUSSION...
Active Weather Forecast for the Panhandles...

Both severe weather and winter weather is in the cards for the
Panhandles with three periods of concern.

First period of concern is this afternoon and evening with the
ongoing severe weather potential. For more information on this
threat, see the mesoscale update discussion section below.

Second period of concern is the snow potential for the northwestern
Panhandles tonight. As a surface cyclone builds northeast into
Kansas tonight, wrap around region on the northwest side of this
cyclone will become the focus for snowfall. Guidance 925, 850, and
725 mb frontogenesis fields indicate a deep area of deformation will
be present across or just adjacent to our far northwestern CWA from
roughly around 00z to 12z tonight. Currently, banding can be seen in
ongoing snow around the Sangre de Cristo mountains, so banding
potential in guidance seems reasonable. There are three main
forecast problems - where this deformation area will set up, how
much moisture will be available to produce snow, and when will rain
change over to snow.

On the deformation/snow axis topic, guidance is doing its typical
thing and differing on the deformation and thus the heaviest snow
axis. Last few runs of CAM guidance focuses the snow along roughly a
Bueyeros NM - Campo CO line. This is in line with the general trend
amongst spectral guidance - the GFS being an outlier - to bring the
higher axis of snow southeastward into the northwestern reaches of
the Panhandles. Trend seems reasonable as the upper trough to our
west has come in a bit more amplified than older runs suggested it
would.

On the moisture question, as is typically the case in higher
elevations, overall moisture in the mid levels will be a limiting
factor. However, the rather soupy airmass in place today as
evidenced by current observations and lingering fog suggests the
frontogenetic dynamics will overcome the usual moisture issues.

On the subject of rain to snow change over time, with the mid levels
being cool the lower level temperatures will be the determinant for
changeover time. While DHT has made it to the 50s this afternoon, OK
Mesonet and CAO obs suggest areas along and northwest of a Texline -
Elkhart KS line are stuck in the 40s. Thus, think change over will
occur in these areas soon enough that they will be dealing with an
impactful enough snow event - 2 to 5 inches - to warrant an
advisory. While progged soundings suggest some instability in the
mid levels, the unstable layers are not directly co-located with the
snow production layer. Thus, current thinking is that snow
accumulations will not reach warning criteria. Nonetheless, will
need to keep an eye on things this evening and tonight as CAMs do
show high end potential of more than 6 inches of snow.

Finally, with wind gusts above 30 mph possible, introduced some
blowing snow into the forecast, particularly for western Cimarron
and Dallam Counties.

Third period of concern comes courtesy of secondary upper low
rotating down from the Pacific Northwest. Guidance is now in
agreement that this disturbance will impact the region but there are
still differences in exact depiction and amount of moisture
available, which looks to be the main limiting factor for snow
amounts with this event. Snow accumulations should be well under
warning level, so will not be issuing any products in relation to
this period at this time.

With a lot happening in the shorter term periods, went with the
model consensus for day 4 onward.

Ferguson

&&

.PRELIMINARY POINT TEMPS/POPS...
Amarillo TX                34  42  23  31  20 /  20  20   5  20  50
Beaver OK                  34  39  21  34  15 / 100  40   0  10  30
Boise City OK              28  34  16  26  10 /  90  80  10  40  30
Borger TX                  35  43  25  33  20 /  30  30   5  20  40
Boys Ranch TX              33  43  23  32  20 /  60  40  20  40  50
Canyon TX                  33  43  23  32  20 /  20  20  10  30  50
Clarendon TX               37  45  26  36  22 /  20   5   0   5  40
Dalhart TX                 29  38  19  28  14 /  90  60  20  40  40
Guymon OK                  32  39  19  30  14 /  90  70   0  20  30
Hereford TX                33  44  23  32  19 /  30  20  20  30  60
Lipscomb TX                36  42  23  36  19 / 100  30   0  10  30
Pampa TX                   34  41  22  33  18 /  40  20   0  20  40
Shamrock TX                38  46  26  38  21 /  80   0   0   5  30
Wellington TX              38  48  27  40  23 /  60   0   0   0  20

&&

.AMA Watches/Warnings/Advisories...
TX...Winter Weather Advisory until noon CST Thursday for the
     following zones: Dallam...Hartley...Sherman.

OK...Winter Weather Advisory until noon CST Thursday for the
     following zones: Cimarron...Texas.

&&

89/89/77

Hazardous Weather Outlook...UPDATED
National Weather Service Amarillo TX
927 PM CST Wed Dec 26 2018

OKZ001>003-TXZ001>020-317-271530-
Cimarron-Texas-Beaver-Dallam-Sherman-Hansford-Ochiltree-Lipscomb-
Hartley-Moore-Hutchinson-Roberts-Hemphill-Oldham-Potter-Carson-
Gray-Wheeler-Deaf Smith-Randall-Armstrong-Donley-Collingsworth-
Palo Duro Canyon-
927 PM CST Wed Dec 26 2018

This Hazardous Weather Outlook is for the Texas and Oklahoma
Panhandles.

.DAY ONE...Tonight.

Snow accumulations expected across the western Oklahoma Panhandle
and the northwestern Texas Panhandle tonight, where a Winter
Weather Advisory is in effect. Additionally, wind gusts as high
as 45 mph may cause patchy blowing snow and reduced visibilities
in these areas.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Snow accumulations will be possible Thursday night through
Saturday across the Panhandles.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible tonight.