Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 011555
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
855 AM MST Thu Dec 1 2016

.SYNOPSIS...After a cold start to the morning, temperatures will
remain below normal through the week. Another storm system will
result in a chance of valley rain and mountain snow Friday night
into Saturday. Dry conditions return Sunday and Monday followed by a
chance of valley rain and mountain snow along with gusty winds on
Tuesday.

&&

.DISCUSSION...The 15Z IR Satellite imagery shows thick cirrus clouds
across the northern two-thirds of the forecast area attm. These
clouds are in response to a disturbance centered off the southern
California coast diving south through the back side of the trough.
This disturbance will move southeast to near Yuma this evening and
then consolidate with another impulse diving southward through the
Great Basin on Friday. Overall forecast package/trends look good
today, as the thick batch of cirrus clouds begins to lift N/NE of
the forecast area as the disturbance moves southeast and the flow
becomes more southwesterly. Still expecting cirrus clouds today, but
more of the thin/wispy variety. Will update the sky grids on the
morning update and also let the Hard Freeze/Freeze Warnings expire.
For more information on the latter periods of the forecast, please
refer to the PREV DISCUSSION section below.

&&

.AVIATION...Valid through 02/18Z.
SCT-BKN cirrus clouds above 20k ft AGL and surface wind less than 12
kts thru the forecast period. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Another low pressure system will move into the
region Friday night and Saturday, resulting in a 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. Another system may impact the region Tuesday and
Wednesday of next week.

&&

.PREV DISCUSSION...A few wisps of cirrus, otherwise another dry and
cold night. Most locations are running 1 to 4 degrees above
yesterday, but still well within range of freeze and hard freeze
values.

Warmer today, then another system digs into the region from the
northwest tonight into Friday morning. This will keep overnight lows
from dropping as far as recent mornings.

We`re able to separate this next system into two phases now with
initial energy coming in from the west tonight, and then a
reinforcing impulse coming down from the north as the pattern re-
amplifies with high pressure building upstream and downstream.
Our chance of precip will come as this part of the system sags into
southern Arizona and northern Sonora Friday night into Saturday
morning. It`s also a hint that our moisture field may end up being a
little more robust than we were originally planning with this
system, so we have bumped our chances of valley rain and mountain
snow up a bit, near low-end chance ranges in valleys to high end
chance ranges in the mountains. Limited QPF with a few hundredths
possible where it manages to rain in the valleys and 1 to 2 inches
of snow above 5000 feet. Our best dynamics, moisture and cool air is
shaping up for our southern mountain ranges with the Chiricahuas and
Huachucas probably having a better chance of reaching 3 inches.

Shortwave ridging Sunday with another stronger looking system lining
up for our area Tuesdayish. Winds are looking strong and gusty under
this feature.

&&

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

&&

$$

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