Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 161022

Area Forecast Discussion
National Weather Service Tucson AZ
322 AM MST Sat Dec 16 2017

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


.DISCUSSION...The weak low meandering slowly across northwest
Mexico is now out of the picture as a shortwave ridge pushes into
our area from the west with the remains of the low now in southern
Chihuahua. One thing we might still be able to get out of it is
moisture if we can manage a southerly flow.

The trough currently digging through the Pacific Northwest will
ultimately be able to tap into some of that moisture. An upper
level jet splitting into and south of our area will help guide
this system quickly into southern California and northern Baja
over the next 24 hours. As this happens, our northeasterly and
easterly flow will become southerly late today. With a favorable
trajectory, it will also tap into some northern Gulf of California
moisture to moisten our atmosphere up fairly quickly later today
and tonight.

Good agreement among most operational and ensemble models with a
trajectory pushing the main low through our area Sunday, with an
associated cold front Sunday afternoon. Best dynamics and moisture
couplet will be Sunday morning into Sunday evening, with the main
event in our corner of the state for a change (southerly moisture
intrusion not expected to be much of a factor for central and
northern portions of the state). Storm total QPF values in the .1
to .3 inch range in valleys with .4 to 1 inch in mountains. Some
enhancement possible with convection Sunday afternoon and early
evening. Snow levels between 7k and 8k feet Saturday evening,
dropping to the 5500 to 6000 ft range Sunday morning. As low as
4500 feet possible with convection in the afternoon and the main
low Sunday evening. 1 to 3 inches between 5000 and 6500 ft, with 4
to 8 inches above 6500 ft. A few spots above 7500 or 8000 ft could
see 8 to 10 inches, but that should be fairly limited in coverage.
Right now we have more of a focus for Mt Graham, the Huachucas,
and the Chiricahuas, but we`ve also included the Catalina, Rincon
and Santa Rita mountains in a winter weather advisory.

Drying from the west Sunday night, but some lingering showers in
eastern areas Monday. Cooler temps and gusty winds at times, but
nothing out of the ordinary for December.

Weak ridging with a warming trend most of the rest of next week,
with another system digging toward our general direction late in
the week. GFS is slower and deeper, we`ll see how it turns out.


.AVIATION...Valid thru 17/12Z.
Clouds AOA 18k ft AGL increasing from west to east into this
afternoon. Lower cloud decks around 8-12k ft agl will develop this
evening with isolated to scattered valley SHRA and mountain SHSN
increasing into Sunday morning. MVFR cigs/vsbys esp near terrain
possible late in the period. Sfc wind ely/sely at mainly less than
12 kts through midday. Speeds increasing out of the south at 10 to
15 kts and a few gusts to around 25 kts. Speeds decrease to less
than 12 kts after sunset. Aviation discussion not updated for TAF


.FIRE WEATHER...Easterly 20 foot winds with speeds of 10 to 15
mph and gusts to 25 mph at times this weekend. Less wind will occur
for the first half of the new work week. Mild and dry weather today
will give way to a weather system bringing cooler temperatures,
valley rain and mountain snow to the area Sunday and Monday. Drier
air and warmer temperatures will then return Tuesday through
Thursday next week.


Winter Weather Advisory above 6500 ft from 6 AM to 11 PM MST
Sunday for AZZ511>514.




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