Cold in Arizona, January 7, 2020

Area Forecast Discussion
National Weather Service Tucson AZ
314 PM MST Mon Jan 6 2020

.SYNOPSIS...Dry conditions and above normal daytime temperatures
will give way to cooler temperatures by the second half of the work
week. A couple systems brush by mainly north of the area creating
occasional breeziness. A stronger system may then bring a chance of
rain and snow showers Thursday into Friday.

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.DISCUSSION...Satellite imagery shows mostly clear skies across much
of the desert southwest this afternoon. A trough was located across
the central CONUS with a ridge starting to build in over the west.

Flow aloft will become more westerly into Tuesday as the
aforementioned ridge moves further onshore and flattens out some. A
tightened surface pressure gradient Tuesday could induce some breezy
easterly winds, particularly near Tucson and through the Gila River
Valley. A weak trough on the backside of the ridge will move out of
the Pac NW and through the Great Basin Tuesday into Wednesday with
little impact on our sensible weather. As such, expect continued dry
conditions with periods of passing mainly high level clouds, and
daytime temperatures peaking a few degrees above normal through
midweek.

Dry conditions persist Thursday morning, but a stronger system will
move south out of the Pac NW, through California and toward the
desert SW. This will likely generate some breezy southwest winds on
Thursday. Improved model agreement today in terms of timing, with
the 06/12Z GFS ensemble mean better aligned with both the
operational GFS and the ECMWF. With these solutions leaning toward a
bit slower progression, decided to keep mentionable PoPs out of the
forecast through Thursday morning. PoPs were then weighed heavily
toward the NBM and blended with WPC Guidance. Right now, the best
chance for measurable precip appears to be Thursday evening/Thursday
night with shower coverage decreasing slightly by Friday morning.

In terms of rainfall, the GFS seems to be tapping into a bit more
moisture compared to previous solutions and the ECMWF remains
relatively more robust with projected QPFs across southeast Arizona.
Since this looks to be a progressive system that should be east of
the state by late Friday afternoon, have kept QPFs on the lower end.
This should generally equate to a few hundredths in the valleys to
perhaps up to 0.20 inches in the mountains. In terms of snowfall,
this system will be on the cooler side with snow levels falling to
between 3500 and 4000 ft Friday morning. This could equate to up to
a few inches of snowfall in the mountains with a dusting to half
inch of snowfall possible in the valleys east of Tucson by the time
all is said and done. Lower heights and thicknesses will also bring
high temperatures down to a few degrees below normal Thursday with
much of the area struggling to get out of the 50s on Friday.

Dry weather should return for the upcoming weekend with high
temperatures remaining a few degrees below normal. There remains an
outside chance of being brushed by to the north by another storm
system late next weekend, but confidence is too low to make any
mention of PoPs with this forecast package.

&&

.AVIATION...Valid through 08/00Z.
SKC conditions through early Tuesday morning with FEW-SCT clouds
expected AOA 20k ft MSL during the day Tuesday. Surface winds mainly
light and variable at 12 kts or less through 08/12Z. Thereafter,
ELY/SELY winds of around 15 kts with gusts 20-30 kts are expected
for KTUS Tuesday morning, tapering off during the afternoon.
Otherwise, winds generally 12 kts or less for most locales Tuesday.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry and mild daytime conditions are expected through
Wednesday. A weather system will move through the region Thursday
night into Friday producing rain and snow showers, with the best
chances of precipitation from Tucson north and eastward. Thereafter,
dry and cool conditions will persist through the weekend. Gusty east
to southeast 20-ft winds of around 15-20 mph are possible through
Tuesday across the mountains and in favorable areas such as the
Tucson Metro. Otherwise, winds will remain light and predominantly
terrain driven aside from Thursday afternoon when stronger westerly
flow develops.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

Carpenter/GL

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