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Area forecast discussion 
National Weather Service Tucson Arizona
305 PM MST sun Jan 25 2015

Synopsis...seasonal daytime temperatures and easterly breezes will
prevail the remainder of the weekend. Increasing moisture from
the south will bring thickening clouds and showers to southern
Arizona Monday into early Tuesday.

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Discussion...not much has changed from this mornings discussion.
High cloud cover should persist through the night. Lower level
clouds should develop later this evening as middle level moisture
advects into southern Arizona from the Pacific. This will set the stage
for our approaching precipitation event. Models are a bit mixed on
the start time for precipitation...but generally agree that precipitation will
begin along the border Monday morning...with the most widespread
precipitation during the evening Monday into Tuesday morning. Current
satellite imagery hints that the upper low is moving slightly
further west than originally anticipated...so that favors the
heaviest precipitation chances generally across Pima and Pinal counties.

As for snow chances...the snow levels will be fairly high in this
event...upwards of 9000 feet. That limits the snow mainly to the
White Mountains. Again...with the further west push of the upper
low...snow totals should be held in the 1 to maybe 5 inch range.

Once this system exits the area Tuesday...the upper ridge over the
western US reamplifies and yet another cut off low develops first
over Nevada...and then settles near Southern California or the Baja California
peninsula Saturday. This system appears to be much wetter than our
Monday system. Models show similar moisture metrics...like precipitation
water or layer relative humidity...but next weekends system has the
potential to bring precipitation for a longer period of time. The
European model (ecmwf)...for example...produces precipitation for well over 24 hours across
Southeast Arizona. The GFS is slightly less optimistic...but given the
trends have been fairly consistent for the last few days...I decided
to increase precipitation chances for the end of the week.

Snow levels will still be high next weekend...but may come in 1000
feet or so lower than Monday. Best estimate right now is that snow
levels will to sit around 8000 feet.

The main concern with next weeks system...in addition to the rain
and snow...will be travel impacts for those heading north for a
highly attended sporting event. Slick roads will be common Friday
and saturady...so drivers should be prepared.

Jjb

&&

Aviation...valid through 26/23z.
High clouds...mainly above 20k feet above ground level...will continue through
26/15z. After 26/15z...lowering clouds are expected through the rest of
the day...with scattered-broken clouds at 5-9k feet above ground level and broken-overcast clouds at
10-15k feet above ground level. Chance of showers after 26/18z. Ely/southeasterly surface wind
at 10-15 kts. Aviation discussion not updated for taf amendments.

&&

Fire weather...east to southeast winds will occur across much of
the area over the next couple of days. Wind speed will be in the
10-15 miles per hour range...with a few higher gusts. There will be a chance of
showers Monday into Tuesday. The best chance for showers will be
Monday afternoon and Monday night. Dry weather will return Tuesday
afternoon through Thursday before another disturbance brings a good
chance of showers late next week and into next weekend.

&&

Twc watches/warnings/advisories...none.

&&

$$

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