Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 131015

Area Forecast Discussion
National Weather Service Tucson AZ
315 AM MST Thu Dec 13 2018

.SYNOPSIS...Expect dry weather to last through Saturday with plenty
of clear nights. Conditions then begin to shift Sunday into the
start of next week, with a slight chance of valley rain and
mountain snow showers. Cooler today then temperatures remain
within a few degrees of normal for this time of year throughout
the remainder of the forecast.


.DISCUSSION...Patches of high clouds were passing through SE AZ
this morning under dry NW flow aloft. Gusty NW winds continue east
of Tucson on back side of upper low that was moving thru SE NM.
Colder morning across most of the area with afternoon highs a few
degrees below normal for mid-December. The upper ridge that is
building west of the state today will move across Arizona on
Friday resulting in highs, for most areas, being 4-7 degrees
warmer than today. High clouds will be on the increase Friday with
mostly cloudy conditions prevailing Friday night into Saturday.
Highs this weekend will be similar to Friday.

An upper level low that develops off the Baja coast on Saturday
will move toward the area on Sunday. Still some model differences
on track and amount of precipitable water that will be over the
area. GFS/NAM are wetter with further west track versus
drier/further east track of the ECMWF. Maintained slight chance of
valley rain/high elevation snow showers for Sunday through early
Monday morning.

Confidence on the low side with respects to weather system moving
across the state on Tuesday. Large spread in the ensembles with
the ECMWF showing a more progressive open wave while GFS is
slower/colder with a closed low over the state. At this time went
with a slight chance of valley rain/mountain snow showers.


.AVIATION...Valid through 14/12Z.
Clear skies to SCT clouds AOA 20k ft AGL thru 14/03Z, then
increasing high clouds and BKN-OVC clouds AOA 20k ft AGL expected by
the end of the forecast period. Except for some gusty NWLY surface
winds in the upper Gila River Valley near KSAD thru 13/16Z, surface
winds will generally be less than 12 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Dry conditions will persist into the upcoming
weekend, with a slight chance of showers late in the weekend and
during the first half of next week. 20-foot winds will be less than
15 mph into early next week across much of southeast Arizona. Expect
east/southeast flow Friday and Saturday, with the strongest winds
generally in and around Tucson.





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