Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 022356 AAA
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
556 PM CST Fri Dec 2 2016

.AVIATION...
For the 00Z TAFs, deteriorating weather conditions from south to
north affecting all terminal sites through tonight with light rain
and light snow likely along with attendant IFR cigs and vsbys as an
upper level storm system well to our southwest affects the region.
Expect precipitation to end from north to south late Saturday morning
and afternoon. However, IFR cigs along with MVFR to IFR vsbys will
persist through Saturday afternoon at all TAF sites.

Andrade

&&

.PREV DISCUSSION... /Issued 350 PM CST Fri Dec 2 2016/

SHORT TERM...

A complex weather system still dominates the short term forecast
period. Current observations show dry air remaining strong at the
surface. However, easterly flow with virga moving north into
portions of the Panhandle region will help to increase moisture in
the mid levels. With lowering bkn to ovc skies across the region,
this process might take a few hours before precipitation reaches
the surface late this afternoon into evening hours. With current
temperatures well into the 40s with an east to northeasterly flow,
precipitation will start as rain across all areas. Going into the
evening hours before midnight, areas across the far western
Panhandles will transition into a mix and then eventually snow.
Light accumulations before midnight are possible across far western
areas.

Challenges to the forecast come as we go from midnight into early
Saturday morning. The central Panhandles region is where the
borderline of sub freezing and above freezing temperatures will
likely set up.  Latest forecast have a wide range of output ranging
from deep cold air within the dendritic growth zone resulting in a
persistent snowfall, to a warmer solution with drier air in the mid
levels with a mixture of rain/snow for the central Panhandles. Areas
across the southeastern TX Panhandle will remain all rain
throughout this event as temperatures will remain above freezing.

Latest 02/12Z hi-res model and probabilistic data shows the onset of
the precipitation starting between 21Z Friday and 00Z Saturday
starting in parts of the southern Panhandle as it progresses
northward throughout the night. Latest model data continues to track
the main low pressure system well to the south across northern
Mexico. As previously mentioned, current observations shows virga
across portion of the Panhandles. As the precipitation fills in
across most of the region throughout the evening into the overnight
hours, some of the GFS/HiRes WRF output runs does advecting mid
level moisture ahead of the main low pressure system into portions
of the central Panhandles near the dichotomy of temperatures above
and below freezing. This could help enhance low level moisture for
an earlier precipitation initiation time. Other outputs shows drier
air working in from the northwest which may damper QPF amounts as
well. Synoptic forcing will be limited to isentropic lift with the
best timing between 00Z and 12Z Saturday as the better established
temperature gradient sets up. Model consensus shows QPF amounts will
range between around a tenth of an inch in the northwestern areas
over a half an inch in the SE TX Panhandle by 12Z Saturday. Winds
will be out of the east and northeast between 10 to 15 kts.
Precipitation will change back to rain for the entire region by 18Z
Saturday as temperatures again warm up above freezing for all of the
Panhandles.

Meccariello

LONG TERM...

Focus will be on the lingering precipitation chances through the
weekend.

Not too much has changed from the previous forecast and things seem
to be in line well. Temperature profiles in the lower levels still
should be monitored closely due to the fact our area of snowfall
could change with only a couple degree differences here and there.
The main change was to end QPF and hence snowfall chances after 00Z
Sunday.

Simulated reflectivity from the HRRR (thru 14Z), NMM, and ARW all
have precipitation lingering around Saturday morning, mainly to our
southeast where mostly rainfall should be occurring. As mentioned
already, it will be interesting to see how our temperatures hold up
tomorrow to support mainly rainfall. There could be a transition
zone of rain or snow. The area of all snow could change as well. It
will depend on how much impact precipitation has on column temps.

Beyond the current activity, there is another cold airmass coming
into the area middle of next week. Models have backed off on
precipitation chances, so I was able to collaborate a little with
the neighbors to decrease those chances in the forecast. Since it
was day 5, there wasn`t too much to hang our hat on. A lot can
change between now and then. Most noteworthy was the GFS ensemble
mean for probability of precipitation of 0.10" over a 12 hour
period. The ensemble mean showed about 10-20% chance mainly to our
north across the Oklahoma Panhandle Tuesday through Wednesday.
These low chances really decreased my confidence for any
precipitation during this time period. That being said, if any
precipitation does form, it should be all snow as temperatures are
cold enough Tuesday night to discern p-type easily.

Guerrero

&&

.AMA Watches/Warnings/Advisories...
TX...Winter Weather Advisory until noon CST Saturday for the
     following zones: Dallam...Deaf Smith...Hansford...Hartley...
     Moore...Oldham...Sherman.

OK...None.

&&

$$


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