Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 242026

Area Forecast Discussion
National Weather Service Tucson AZ
127 PM MST Tue Jan 24 2017

.SYNOPSIS...Aside from some some isolated showers in the favored
upslope areas east of Tucson, dry air has moved into the area, and
will remain in place through the end of the week. This will result
in chilly nights tonight and again Wednesday night, followed by a
gradual warming trend into the weekend.


Longwave troughing remains the dominant weather feature on water
vapor imagery this afternoon, although a series of shortwave troughs
can be seen across California and Nevada. Across SE Arizona, skies
remain mostly clear across western Pima Co but are rather congested
to the east thanks to early morning sunshine, steep mid level lapse
rates, and lingering mid level moisture. Precipitation thus far
since daybreak has been minimal but still enough to warrant low end
PoPs through the end of the day east of Tucson.

Primary short-term forecast concern is on overnight temperatures
tonight into Wednesday morning. All deterministic guidance as well
as locally error corrected ensemble guidance suggests a good chance
of lows dropping to, or slightly below freezing tonight. As this is
the first noteworthy cold event across the deserts in over a month,
a Freeze Warning is warranted and will remain in place unchanged.
Temperatures will be similar Wednesday night into Thursday as well,
although it doesn`t appear temps will fall sufficiently to warrant
any sort of Hard Freeze Warning.

Dry weather with below normal temperatures will continue through
Thursday and into Friday, although some of the far eastern locations
along the AZ/NM border could see some increasing clouds courtesy of
a fast moving trough moving through the Four Corners. Latest output
from the NAEFS suggests PoPs in these area should remain below 10
percent thanks to over-land trajectory of the trough and dry air
that will already be in place. Exactly what happens to this trough
after it moves through the area is still up for debate. Some of the
deterministic models are trying to indicate it will close off and
possibly retrograde back into southern Arizona next week while
others maintain a progressive flow with ridging taking shape. I
maintained a dry forecast with slowly moderating temperatures per
GEFS mean and latest available NBM guidance which seems the most
plausible solution at this point.


.AVIATION...Valid through 26/00Z.
Congested cu along with some occasional breeziness is expected
through late afternoon at all TAF sites, although skies will quickly
clear after sunset and winds will become light/vrb. Mostly clear
skies and light winds are anticipated through the day Wednesday.

Aviation discussion not updated for TAF amendments.


Isolated mountain showers will quickly dissipate this evening with
dry weather forecast for the remainder of the week. There is a
chance of increasing clouds and occasional breeziness on Friday as a
fast moving trough moves through the Four Corners into AZ/NM
although critical thresholds are not forecast to be realized at any
time with this trough. Aside from this trough, winds will follow
typical upslope and downvalley patterns through early next week.  A
gradual warming/drying trend is anticipated this weekend into next
week with precip-free conditions.


    Freeze Warning from midnight tonight to 9 AM MST Wednesday
      for AZZ502-504>506.




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