Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 302116

Area Forecast Discussion
National Weather Service Tucson AZ
215 PM MST Wed Nov 30 2016

.SYNOPSIS...Another widespread freeze or hard freeze is in store for
Southeast Arizona tonight. Temperatures will remain below average
through the week, and another storm system may bring a chance of
valley rain and mountain snow Friday into Saturday.


.DISCUSSION...Water vapor imagery and 30/12Z upper-air plots show a
large area of low pressure centered over the Upper Midwest/Great
Lakes region with the associated trough axis extending southwest
into the central and southern plains. Meanwhile, closer to home a
dry northwest flow aloft continues across the Desert Southwest, with
a weak disturbance currently moving southeast across northern Baja.

The 30/12Z KTWC sounding revealed a very dry airmass in place with a
precipitable water value of 0.18 inches, which is 0.28 inches drier
than 24 hours ago.

IR satellite imagery shows clear skies across much of the
southwestern states. With clear skies expected to continue
overnight, and with light to near calm winds, expect another night
with freezing and subfreezing temperatures for early Thursday
morning. That said, freeze and hard freeze warnings continue late
tonight and into early Thursday morning for parts of my forecast

Another system will affect our forecast area late this week and
early this weekend, resulting in a slight chance of valley rain and
mountain snow. Yet another system is progged by the GFS to affect us
early next week. However, models are at odds with regard to the
potential for showers, with the GFS much more aggressive than the
drier ECMWF. That said, for now I used a blend between the two
models and for now I have slight chances for mountain showers
starting Monday night and continuing through Tuesday night. Due to
the continued uncertainty, the POP forecast that I have decided to
utilize may change significantly between now and early next week,
depending on how subsequent model runs handle this approaching


.AVIATION...Valid through 02/00Z.
SKC conditions/clear skies thru 01/09Z. Aft 01/09Z, increasing
high cirrus clouds above 20k ft AGL. Surface wind less than
12 kts thru the forecast period. Aviation discussion not updated for
TAF amendments.


.FIRE WEATHER...Dry conditions will occur through Thursday. A low
pressure system will then move into the region Friday and Saturday,
resulting in a slight chance of valley rain and mountain snow. This
system may also produce some gusty east winds. Dry conditions are
expected behind the system Sunday and Monday. A slight chance of
showers returns Tuesday and Wednesday of next week.



Hard Freeze Warning from midnight tonight to 9 AM MST Thursday
for AZZ503.

Freeze Warning from midnight tonight to 9 AM MST Thursday for




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