Area Forecast Discussion
Issued by NWS Tucson, AZ

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158
FXUS65 KTWC 112136
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
236 PM MST Wed Jan 11 2017

.SYNOPSIS...Expect dry conditions with mild daytime temperatures
through Thursday. A few sprinkles possible Friday, then a low
pressure system will then bring a chance of valley rain and
mountain snow over the weekend along with cooler temperatures. Dry
conditions with warmer temperatures will return early next week.
Another storm system may impact the area later next week.

&&

.DISCUSSION...Our zonal flow will slowly start to buckle as
energy carves down the west coast over the next 48 hours. Our 12z
sounding showed layers of moisture above 700mb but not much below
that, with a total PW around .4 inches. Patches of mid and high
cloud at times with temperatures a few degrees above average.

We start to pick up a solid southwesterly flow Friday morning with
moisture increasing from the southwest. Initially this will be
additional mid level moisture and we could have some virga or
terrain induced light showers in a few spots as early as Friday
afternoon.

The trend on this system has been a deeper and slower trajectory
with a bit less higher latitude support after the initial split.
A stubborn ridge over southeastern states will keep the low from
digging too far south (unless it decides to completely cut off),
so it is still expected to be a weather maker for southern Arizona
and northern Sonora. Initial light shower activity in warm sector
upslope early Saturday. Best moisture and dynamics come together
between Saturday afternoon and Sunday morning. Some wrap-around
will keep some showers around Sunday afternoon and Sunday evening.

Snow levels will start around 8k feet late Friday, falling to 7.5k
feet Saturday, then as low as 5.5k - 6k feet Sunday. A few spots
could briefly drop as low as 5k feet with weak convection. Total valley
precip in the .1 to .6 inch range, and snow amounts around 5 to 10
inches above 7k feet, maybe 1 to 4 inches between 6k and 7k feet
as snow levels fall Sunday. We may end up needing a snow advisory
for sky islands.

Dry and warmer early next week with another system lining up for
our area late next week. Some early signs that it may be stronger
and colder than the one approaching the area now, with a pattern
change that would establish an overall mean trough position
through the entire (western) region.

&&

.AVIATION...Valid through 13/00Z.
FEW-SCT clouds at 11-14k ft AGL and BKN clouds AOA 20k ft AGL
thru the forecast period. Surface wind generally less than 12 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions with mild daytime temperatures
through Thursday. A low pressure system will then move into the
region late in the week, resulting in a chance of valley rain and
mountain snow over the weekend. Dry conditions are expected to
return Monday through Wednesday of next week. 20-foot winds
through much of the forecast period will be terrain driven and
less than 15 mph.

&&

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

&&

$$

Meyer

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