Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 201606

Area Forecast Discussion
National Weather Service Tucson AZ
900 AM MST Fri Jan 20 2017

.SYNOPSIS...A winter storm will spread valley rain, significant
mountain snow and gusty winds through Arizona today into Saturday.
Snow levels will lower through time, potentially reaching the valley
floors east of Tucson Saturday. After a break in the weather on
Sunday, another weaker storm system is likely on Monday and Tuesday.


.DISCUSSION...Precipitation was a little slow to get started last
night but has begun to move into the area. Currently the most
significant precipitation is mainly north of I-10 with lighter
showers to the south.  Of note is the current showers are very
shallow in nature and much of it is being overshot by the radar to
the south as precip is being recorded on some of the gauges to the
south with very limited radar returns.  Expect much of the same
through at least the first half of the day with showers increasing
in coverage and intensity late today into tonight where widespread
valley rains and significant mountain snows are expected. There is
potential for a lightning flash or two tonight as well and that
covered in the current forecast. It is interesting to see the snow
amount forecasts on the UA mesoscale models as they pound Mt Lemmon
and Mt Graham. Will have to see how that verifies.

The other issue to deal with is the wind which will pick up
significantly tonight, especially over the mountains where gusts to
70 mph is very possible. Currently have a wind advisory up for a
large part of the lower elevations and as noted earlier will need to
look at the potential for a high wind warning in the favored area
around Sierra Vista. The Winter Storm Warning is all encompassing so
the wind and snow is covered there for the mountains. I sent out a
quick update to tweak a few things in the first 24 hours but thats
it for now.

Reminder from the previous discussion...The storm will push off to
our east by late in the day Saturday with leftover precipitation
tapering off. Generally dry on Sunday with shortwave ridging aloft.
Thereafter, another system is progged to impact the desert southwest
Monday into Tuesday. However, this system will be considerably
weaker with lower QPF values. Snow levels will be down to as low as
4000 feet once again with this system.

Broad troughiness aloft is expected to remain over the region later
Tuesday into Wednesday, thus will continue with slight chance PoPs
during this time. If indeed enough moisture remains for precipitation
during Tuesday night into early Wednesday, snow levels will be even
lower, perhaps 3000 to 3500 feet. Thereafter, dry but cool conditions
are expected into late next week with a possible freeze in Tucson on
Thursday morning.


.AVIATION...Valid through 21/12Z.
Scattered -SHRA and mountain -SHSN this morning mainly north of I-10
followed by more numerous SHRA/mountain SHSN this afternoon into
Saturday morning areawide. ISOLD TSRA possible tonight. Expect
widespread MVFR conditions and occasional IFR conditions
particularly this afternoon into Saturday. Surface wind into this
afternoon will mainly be swly 8-18 kts with gusts to 25 kts. Surface
wind tonight will be swly/wly 15-35 kts with gusts of 30-50 kts.
Surface wind diminishing somewhat after 12Z Saturday but still gusty.
Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Expect numerous valley rain and mountain snow
showers this afternoon into Saturday. Dry conditions will occur
Sunday, then scattered to numerous valley rain and mountain snow
showers will return Monday into Tuesday. Dry conditions will then
prevail by next Thursday. Strong and gusty southwest to northwest
winds will also occur this afternoon into Saturday, then 20-foot
winds will generally be terrain driven less than 15 mph during much
of the upcoming week.


Winter Storm Warning until noon MST Saturday for AZZ510-511-514.

Wind Advisory from 8 PM this evening to 8 AM MST Saturday for

Winter Storm Warning from 5 PM this afternoon to noon MST Saturday
for AZZ512-513-515.



Aviation/Fire Weather...Cerniglia/Francis

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