Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 160340
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
840 PM MST Sun Jan 15 2017

.SYNOPSIS...Lingering moisture will provide isolated to scattered
valley rain and mountain snow showers into Monday evening. Expect
mainly dry conditions with a warming trend Tuesday into Thursday. A
couple of storm systems will then bring more valley rain, mountain
snow and much cooler temperatures Thursday night into next weekend.
Some snow may occur to valley floors east of Tucson by Saturday.

&&

.DISCUSSION...Isolated valley rain and mountain snow showers
continued across southeast Arizona this evening. The bulk of rainfall
amounts or snow accumulations during the past few hours has been
quite light, and only light amounts/accumulations are expected the
rest of tonight. Snow levels were generally in the 6500-7000 feet
range as of 830 PM MST.

Meanwhile, surface observations depicted low clouds covering much of
southeast Arizona, and IR satellite imagery depicted colder-topped
clouds indicative of mostly cirrus spreading eastward into western
and southern sections from northwest Sonora Mexico. Given some small
temp/dewpoint depressions, particularly south-to-southeast of Tucson,
am somewhat concerned about fog formation later tonight.

However, the extensive cloudiness, particularly with cirriform clouds
spreading across portions of the area, will likely hinder fog
development. At any rate, will opt to insert patchy fog for
elevations below 5000 feet south-to-southeast of Tucson the rest of
tonight and into mid-morning Monday. Otherwise, the official forecast
of mostly cloudy to cloudy skies and a slight chance of valley
rain/mountain snow showers into Monday morning appears reasonable.

Please refer to the additional sections for further detail.

&&

.AVIATION...Valid through 17/06Z.
Isolated to scattered -SHRA and mountain -SHSN especially KTUS
vicinity eastward to the New Mexico border into Monday evening. This
precip will result in occasional MVFR conditions and perhaps brief
IFR conditions, and higher terrain will be obscured. Surface wind
will generally be variable in direction less than 12 kts. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...A gradual drying trend will occur early this week,
but lingering moisture will provide a slight chance of valley rain
and mountain snow into Monday evening. Precipitation amounts will be
quite light. Dry conditions will then prevail across much of the
area Tuesday into Thursday. Thereafter, a couple of storm systems
will have the potential to bring more significant valley rain and
mountain snow Thursday night into next weekend. 20-foot winds will
be terrain driven and generally less than 15 mph through midweek
followed by some gusty southwest winds with the storm systems.

&&

.PREV DISCUSSION /218 PM MST/...Scattered light showers continue
across parts of the area as plenty of moisture is left behind as the
storm that brought it now pummels Texas with significant
thunderstorms. The showers will diminish after sunset but
with the upper level trough remaining over the region there will
remain a threat of a shower or two through the night. The next weak
system drops into the bottom of the trough tonight into Monday
leaving the axis right over the central part of our area. While the
position of this feature leaves us out of forcing of any significance
it does up the odds a bit for afternoon convection developing.
Convective allowing models pointing toward that thought with
convection developing over the higher terrain during the afternoon.
Thus maintaining chance pops over the high terrain. Will remain on
the cool side Monday.

The upper trough very slowly eases off to the east Tuesday into
Wednesday allowing for some drying and afternoon temperatures slowly
climbing back up to mid-January norms. The trough is close enough and
there remains enough moisture that a shower is still possible
mountains near the New Mexico border on Tuesday.

Then attention turns to late next week where the long range models
have been nicely consistent indicating a couple of significant
systems moving across the area. If all holds, the first will approach
western areas late Thursday with the primary impact being Thursday
night into early Friday with some valley rain, mountain snow and
cooler temperatures, similar to what just went through. However this
one basically sets us up for the stronger system right on its heels
which at this time is modeled to be wetter and colder and hit the
area later Friday through Saturday. This system has the potential for
snow further down the mountains and into some of the high valleys. We
will be watching this system closely over the next few days so stay
tuned.

Then after a couple of dry days there is potential for yet another
system early the following week. This is what last winter (the super
El Nino) should have looked like.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Francis
PREV DISCUSSION...Cerniglia

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