Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 121048

Area Forecast Discussion
National Weather Service Amarillo TX
448 AM CST Thu Jan 12 2017

.SHORT TERM...Today and Tonight...For today, the sfc cold front has
moved through much of the forecast ahead of all models. This is
reflected in current temps across northern and eastern sections which
are significantly colder than any of the numerical weather MOS
guidance for 09Z this morning. The position of this frontal boundary
will largely dictate highs today, with a decent temperature gradient
likely. Have followed the coolest NAM MOS guidance for highs today
based on current obs and frontal position.

For tonight, expect increasing cloud cover ahead of a strong upper
level low pressure system which is progged to close off while
digging southward down the California coast to a position near or
just west of Los Angeles by 12Z Friday. Short range models are in
good agreement through 12Z Friday handling this upper level low and
were accepted.



.LONG TERM...Friday through Monday...Model run consistency continues
to be problematic during this forecast period, though there is some
similarities in the GFS, ECMWF and NAM concerning placement of higher
QPF amounts. In collaboration with neighboring offices, have utilized
the GFS to assess QPF amounts but have taken note of a continued warm
bias in the overall forecasted temperatures in the lower boundary
layer. The latest forecast leans on the ECMWF and NAM to help
establish overall precipitation types for this upcoming winter storm.
The cold front mentioned in the prior section of the AFD is expected
to remain south and west of the forecast area until about Sunday
evening, when a cold core upper low is progged to pass over the
southern and eastern portions of the combined Panhandles. Moist
southwesterly flow aloft ahead of this upper low, combined with a
warm nose around 3000 to 7000 feet above the surface, will produce
the potential for light freezing rain and/or ice pellets starting
midday Friday. Surface temperatures should warm to around 35 to 40
degrees in the southwestern Panhandles Friday afternoon, before day
time heating is lost and the entire Panhandles fall below freezing.

As the upper low continues to approach the region, increasing
moisture advection into the area will bring freezing rain to the
entire region by Friday night to Saturday morning. Ice accumulations
could approach about a tenth of an inch during this period for the
entire region, with the exceptions being in the far western Oklahoma
Panhandle and extreme southwestern Texas Panhandle. During the day
Saturday, temperatures could recover for most of the region to above
freezing, though confidence in temperature profiles near the sfc
increasing to above freezing is low given ongoing cloud cover and
precipitation. Temperatures should fall below freezing once more for
the northern 2/3 of the combined Panhandles which, due to continued
overrunning of warm air aloft, will once again bring another round
of freezing rain. QPF amounts is expected to be higher during this
period due to favorable upper level diffluence with the ejecting
negatively tilting trough. This heavier QPF amount will result in
flowing streams and ponding, which will slow ice development. Have
opted to use a lower ice-to-liquid ratio of around 0.3 to 0.5:1 to
account for this possibility.

On Sunday, the upper low is progged to pass over the northwestern
combined Panhandles, with a reinforcing shot of cooler air coming in
behind its passage. Much cooler temperatures aloft will help
transition precipitation to snow in the northwestern portion of the
combined Panhandles, with a mix of snow and rain under regions of
the upper low`s passage Sunday morning. As the low lifts towards
Kansas, lower level flow will briefly switch towards the southeast
Sunday afternoon (bringing rain). Cold air will filter in behind the
exiting low Sunday night, switching nearly the entire region to snow
or rain-snow mix late Sunday into early Monday. Height rises, and
drier downsloping air from the northwest, should aid in decreasing
precip chances Monday afternoon with snow possible over the extreme
northwestern combined Panhandles.

With all of the above said, have retained the Winter Storm Watch and
extended the watch westward to include Texas and Hansford counties
due to higher forecasted ice accumulations. Confidence is not yet
high enough to extend the Winter Storm Watch into the western
Panhandles due to uncertainty of meeting warning criteria and run-to-
run inconsistencies.


...Monday Night through Thursday...For the period Monday night
through Thursday, have retained a dry forecast at this time along
with some moderation in temperatures. Medium range models are not in
very good agreement with the overall pattern during this time frame,
which is not unusual given the fast flow projected into the wrn
states and the various embedded upper level shortwave trofs within
this flow. Decided to trend towards a model consensus solution from
Monday night through Thursday pending better model agreement.



.AMA Watches/Warnings/Advisories...
TX...Winter Storm Watch from Friday morning through Sunday morning
     for the following zones: Hansford...Hemphill...Lipscomb...

OK...Winter Storm Watch from Friday morning through Sunday morning
     for the following zones: Beaver...Texas.



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