Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 231019

Area Forecast Discussion
National Weather Service Tucson AZ
319 AM MST Fri Feb 23 2018

.SYNOPSIS...A passing system will bring gusty winds this
afternoon and evening with a few showers near the mountains
tonight. A brief warming trend early next week will be followed
by another stronger winter storm system around the middle of the
week, with a decent chance of valley rain and mountain snow late
Tuesday into Wednesday.


.DISCUSSION...A storm system digging through the Great Basin into
the central Rockies over the next 24 hours will bring gusty winds
to our area this afternoon, but the enhanced surface gradient is
not expected to be strong enough for advisory levels even in more
wind prone eastern areas. Most of the dynamics and moisture will
remain north of our area, with a few mountain snow showers
possible for SE AZ. Best chances will be in the mountains of
northern Graham and Greenlee county (NE of Tucson).

The pattern will remain favorable for winter weather activity into
next week, with a mean trough position across the region
sandwiched between persistent ridges north of Hawaii upstream and
near southeastern states downstream. Another weaker system will
brush by north of our area Saturday night with a brief localized
shortwave ridge embedded in the larger pattern bringing warmer
temperatures Monday.

Our next big weather maker is shaping up for Tuesday or Wednesday
next week. The western Bering Sea system we were watching last
night is pushing toward southern Alaska as an unseasonable ridge
shifts from the Aleutian Islands into the Gulf of Alaska over the
next 24 hours. At that point it will be free to make a strong move
southward on the back side of the mean trough position, then take
a deeper trajectory and back a little further west as it dives
southeast of a positively tilted ridge through the eastern Pacific
and redefines the western extent of the trough. Operational,
ensemble and model blends are in good agreement for this general
scenario with only modest differences in timing. We`ll continue to
ramp up precip chances in the forecast for late Tuesday into
Wednesday for our area. Based on current analysis, identification
and progression of the large scale pattern and model agreement,
our confidence is increasing even at 120 hours.


.AVIATION...Valid thru 24/12Z.
SKC conditions this morning becoming FEW-SCT 6-10k ft AGL this
afternoon, especially from KTUS north and east. Isolated -SHRA and
higher terrain -SHSN mainly KSAD vicinity and NE into the White Mtns
this evening and overnight. Light SFC wind this morning increasing
out of the NW to SW this afternoon at 12-20 kts with gusts to near
30 kts. The strongest winds are expected east of KTUS. Speeds will
decrease to 8-14 kts overnight into Saturday morning. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...A fast moving system north of the area will bring
a slight chance of showers mainly across the White Mountains tonight
into Saturday morning. Dry conditions will then prevail Saturday
afternoon into Tuesday morning. Thereafter, a stronger storm system
will bring scattered valley rain and mountain snow showers Tuesday
and Wednesday. Dry conditions should return by the end of next week.

Expect gusty southwest to northwest 20-ft winds this afternoon and
again next Tuesday at 15 to 20 mph. A few spots may briefly hit red
flag criteria across extreme southeastern fire zone 152 this
afternoon. 20-ft winds will generally be terrain driven at 15 mph or
less at other times over the next week.






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