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Area forecast discussion 
National Weather Service Tucson Arizona
845 PM MST sun Dec 21 2014

Synopsis...a dry northwest flow will result in patches of high
level clouds with temperatures near normal to start the week. A weak
cold front will move through Monday night bringing slightly cooler
temperatures especially east of Tucson Tuesday. A storm system will
stay mainly to our north for the end of the week with few snow
showers for the White Mountains.


Discussion...sheaves of mainly cirrus level moisture...dense at
times...streaming in from the north this evening. Flow amplifying
with strong ridge building just offshore in the eastern Pacific with
Southeast Arizona in between major features. The strong system
developing for the northern and Central Plains over the next 48
hours will just guide one piece of energy for a glancing blow
passing northeast of our area. Current forecast handles this well
with some cooling (especially for eastern areas) as a generally dry
cold front backs down the eastern portions of the state late Monday
into Monday night. Minor updates for first period trends. Please see
previous discussion for additional details.


Aviation...valid through 23/04z.
VFR conditions at all terminals with broken to overcast high clouds
generally above 20k feet. Some clearing from the north Monday. Surface
wind will be diurnal and generally less than 10 kts through 22/21z.
Breezy northwest winds developing thereafter...stronger winds south
and east of ktus. Aviation discussion not updated for taf amendments.


Fire weather...generally dry conditions through the period with
just a few snow showers possible late in the week in the east
central mountains (including northern Greenlee county). A system
passing to the north will bring breezy to locally windy conditions
Monday afternoon across eastern areas...especially Gila Valley.
Still breezy at times Tuesday and Wednesday. Dew points will drop
significantly following a frontal passage from the north late Monday
and Monday night...resulting in lower humidity levels even with
colder temperatures.


Previous discussion...lots of mainly high clouds over the area this
afternoon under north-northwest flow aloft. These clouds will be around...but
in a thinning fashion...tonight into Monday morning resulting in a
mix of partly to mostly cloudy conditions. Lows tonight...even with
the varied amounts of cloud cover...will be similar to what occurred
this morning.

Weak upper level trough moving down front side of upper high well to
our west will push through the 4 corners region Monday afternoon and
into New Mexico Monday night. A north breeze will kick up as
pressure gradient tightens. Might see a brief flurry or two in the
whites late Monday afternoon into Monday evening.

Upper trough deepens over New Mexico on Tuesday with cooler air
settling in the eastern zones along with gusty northwest winds. Interesting
to note that NAM/GFS MOS guidance is going much stronger with the
winds in the eastern zones versus what we are forecasting and what
some other model guidance is showing. Something to watch. Highs east
of Tucson on Tuesday will 3-6 degrees cooler than Monday.

North-northwesterly flow aloft for the rest of the week with a couple of weather
systems moving through the 4 corners with models at odds of depth of
these system. The whites could see a flurry or two from these


Twc watches/warnings/advisories...none.



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