Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 160407
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
907 PM MST Fri Dec 15 2017

.SYNOPSIS...Dry conditions will prevail across southeast Arizona
through Saturday. A quick moving weather system will bring colder
temperatures, valley rain and mountain snow showers Saturday night
and Sunday. Slightly warmer temperatures and dry weather will
return early next week before another system moves into our area
late next week.

&&

.DISCUSSION...The sky was clear across southeast Arizona this
evening with leading edge of high clouds, associated with our
weekend storm system, extending from Salt Lake City to Los
Angeles. Water vapor imagery showed an upper level trof extending
from Washington southwest to off the central California coast. Its
the southern portion of this trof that our upcoming winter storm
will be developing and driven south on the strength of 100+ knot
300 mb jet.

Now to our south there is an upper level low over the southern
Gulf of California with plenty of low-mid level cloud cover over
the southern half of Chihuahua Mexico. The srn GLFCA upper low
will not be player in our next of the cacti, but the moisture
will.

As the upper level trof continues to move east into the
intermountain west on Saturday, high clouds will be overspreading
the area. Later in the afternoon an upper level low will start to
form over southern California as the upper jet continues to dive
south along the California coast. The moisture over northern
Mexico will also start to advect north toward SE Arizona.

With the lower levels still on the dry side, will spend the later
part of Saturday afternoon into the early evening hours moistening
up from top down. Then the upper dynamics increases as the upper
low moves closer to the area with scattered showers developing.
Snow levels will be around 8000 ft early Saturday evening then
fall to around 5500 ft by Sunday morning then around 4500 ft
Sunday afternoon/evening. Convective nature of showers may briefly
lower snow levels down to around 4000 ft Sunday evening. No
change this evening on forecast snow snow amounts, which will vary
across the mountain ranges, with a locations above 8k feet
getting up to 6 to 8 inches, with 3 to 5 inches between 6k and 8k
feet, maybe 1 inch at 5k feet. Later shifts may hoist up a low end
snow advisory for Sunday. Valley QPF totals mostly in the tenth
to quarter inch range with locally higher amounts, especially near
the higher terrain. Also can`t rule out a few lightning strikes
with this system. Oh and lets not forget its going to be cooler
with highs on Sunday about 5-7 degrees below normal.

&&

.AVIATION...Valid thru 17/00Z.
Clear thru 17/12z then increasing high clouds from west to east
thru end of pd. Sfc wind ely at mainly less than 12 kts overnight
into Saturday morning. Sfc wind bcmg s-sw 8-15 kts Saturday aftn
with lclzd hier gusts to 25 kts. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Easterly 20 foot winds with speeds of 10 to 15
mph and gusts to 25 mph at times. Otherwise, mild and dry weather
will prevail into Saturday. A stronger weather system will bring
cooler temperatures, valley rain and mountain snow to the area
Sunday. Drier air and warmer temperatures will then return next
week.

&&

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

&&

$$

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