Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 172102

Area Forecast Discussion
National Weather Service Tucson AZ
202 PM MST Tue Jan 17 2017

.SYNOPSIS...Isolated showers over eastern areas will end this
evening leaving dry and seasonal weather through early Thursday. Then
a series of storms will spread valley rain, mountain snow and gusty
winds over Arizona Thursday night into Saturday. Snow levels will
lower through that time potentially reaching the valley floors east
of Tucson by Saturday. After a break in the weather another storm
system is likely early next week.


.DISCUSSION...A few very light showers were noted over eastern areas
but doubtful much is making it to the ground. These will end this
evening with skies gradually clearing. After a second day of drying
would not expect as much fog as this morning so have left it out of
the forecast.

Wednesday into early Thursday will be a dry period as a short wave
ridge builds across the area. winds will be light with plenty of sun
Wednesday and temperatures only a couple of degrees cooler than

The "fun stuff" begins Thursday night and continues into Saturday as
a two part weather punch affects the region with significant
precipitation expected. The first system will spread precipitation
across southern AZ mainly Thursday night into early Friday morning.
There has been a bit of back and forth on the start time but at this
time I feel it will be the evening hours generally. Models were
running reasonably moist with this system until yesterday when they
dried it out but they have now returned to their previous thought.
Snow levels with this first system will start out near 6500 feet and
drop to around 5500 feet and after doing a QPF blend of models and
WPC forecast then trimming a bit still ended up with advisory snow
amounts over our mountains from the Catalinas north. Will also be
looking at rather breezy conditions mainly across the mountains as
this passes.

The precipitation will taper off the middle part of Friday then
begin to pick back up again later in the day with the bulk of the
precipitation occurring Friday night into early Saturday morning with
this second system. This will be the heavier precipitation producer
with snow levels Friday evening around 6000 feet lowering through
the night, potentially to 4500 Saturday morning. The bulk of the snow
is expected above 5500 feet where warning amounts are possible Friday
night into Saturday. Again it will likely be windy mainly across the
mountains especially the southern ones where 25-35 mph winds and
higher gusts are expected.

So, with a middle of the road QPF forecast, valley rainfall amounts
of 0.50 - 1.20 inches is likely with locally higher amounts. For
snow, across the southern mountains (border area) we could end up
with 2-4 inches of snow for Thursday night and 5-12 inches Friday
night. For the Catalinas northward could end up with 5-8 inches
Thursday night and 8-14 inches Friday night. At this time for
simplicity and coordinating with neighbors went with a Winter Storm
Watch above 5500 feet for the entire period which will likely be
broken up into advisories and/or warnings and adjusted in the future
as details become clearer.

This system moves east leaving behind a dry Sunday with another
system passing through the region early next week. While this
continues to modeled as a rather vigorous and cool system it dosn`t
look as wet as this weekend system.


.AVIATION...Valid through 19/00Z.
Isolated -SHRA/-SHSN far eastern areas will dissipate this evening.
SCT locally BKN clouds around 5k-9k ft AGL and SCT-BKN clouds above
20k ft AGL diminishing overnight with mostly clear skies after 18/10z.
Surface wind will be variable in direction mostly less than 10 kts
then becoming westerly 6-12 kts Wednesday afternoon. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...The few showers across zone 152 will end this evening
leaving dry weather into early Thursday with generally light winds
and elevated humidity levels. Then a series of storms will spread
a good amount of precipitation across the area late Thursday into
Saturday with snow levels near 6000 feet Thursday night and Friday
dropping near or a bit below 5000 ft Saturday. Gusty west to
southwest winds are expected at times through this period especially
across the mountains. Dry weather returns Sunday into Monday before
another storm affects the area early next week.


Winter Storm Watch from Thursday evening through Saturday
morning for AZZ510-511-514.

Winter Storm Watch from Friday afternoon through Saturday
morning for AZZ512-513.



FIRE WEATHER...Cerniglia/Glueck

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