244
FXUS65 KTWC 081459
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
759 AM MST Wed Jan 8 2025

.UPDATE...Just ran a quick update to add areas of blowing dust into
the forecast through 03Z this evening which is the period of
strongest winds. We`re seeing areas of blowing dust with reduced
visibility in spots of 2 to 6 miles. This blowing dust is certainly
exacerbated by the antecedent dry conditions.

Previous Update 426 AM MST...Quick update to cancel the Cold Weather
Advisory early. Increased winds and cloud cover are both working to
keep temperatures from dropping enough to pose cold or wind chill
threats this morning.

&&

.SYNOPSIS...

A low pressure system over the desert southwest will result in
colder temperatures, breezy to windy conditions, and chances for
precipitation today. Although precipitation amounts are expected
to be light, the valley floors east of Tucson may be impacted with
light snowfall accumulations. After this system departs,
widespread sub-freezing temperatures are expected across Southeast
Arizona Thursday and Friday mornings.

&&

.PREV DISCUSSION... /issued 312 AM MST Wed Jan 8 2025/

Early this morning, a closed upper low was centered over the far
northern edge of the Gulf of California, while a 100 knot jet
streak was over the southwest quadrant and slowly rounding the
base of the low. As the low becomes stacked this morning, the
pressure gradient will tighten through the surface, with the
surface low centered over northwest Sonora and the northern gulf.
Water vapor and GOES precipitable water imagery indicates the
presence of mid-level dry air still over far southern Arizona.
While there have been an increase in modest radar returns aloft
early this morning, the jet streak aloft yet to arrive and the
antecedent dry air will likely delay more widespread precipitation
until around mid- morning. This has been supported by recent
high- resolution models, which begin to introduce rain/snow
showers by 9 AM.

In the meantime, east to southeast winds will increase this
morning with the tightening pressure gradient. Areas open to
southeasterly flow should reach sustained levels exceeding 30 mph
at times, keeping the current Wind Advisory in good standing.
Additionally this morning a Cold Weather Advisory is in effect
for wind chills into the teens in valleys of Graham and Cochise
counties. Winds and cloud cover may be able to keep temperatures
in these areas from completely tanking, so the headline may need
looking at again as we approach sunrise.

Chances for precipitation increase as the upper level jet streak
rotates around the low today. Atmospheric moisture content
continues to look fairly unimpressive, with forecast liquid
precipitation totals through Thursday in the few hundredths to
two tenths of an inch range. A very isolated quarter inch can`t be
ruled out in far southeastern corners of the state or eastern
slopes exposed to upslope flow. With snow levels dipping below
3000 feet, areas near and east of Tucson may see light snow mixed
with rain, with light accumulating snow possible above 4000 feet
today. It`s questionable whether or not the Tucson area will see
the moisture arrive in time this morning before the wet bulb
temperature warms too high for snowflakes, but there may be a
brief window of opportunity.

Overall highest precipitation and accumulation chances gravitate
towards the favorable divergent area of the upper level jet streak,
in this case Graham, Greenlee, and Cochise counties. Chances
linger here through Thursday, however with very light
precipitation potential after this evening.

Cold temperatures settling in behind the then exiting upper low
should produce well below freezing morning lows in eastern
valleys, and near to just below freezing temperatures in the
Tucson metro. These cold lows should stick around into the weekend
as a dry troughing pattern persists. How cold Tucson becomes
Thursday morning may depend on how low level moisture lingers, but
there is enough support that at least low lying areas should drop
below freezing that the Freeze Watch was upgraded to warning.

&&

.AVIATION...Valid through 09/12Z.

Increasing coverage of cigs at 3k-5k feet this morning with
isolated to scattered -SHRA/-SHSN, with more coverage in southern
areas near KOLS-KDUG. Brief MVFR possible with any -SHSN. East to
southeast winds increase and become 15-25 kts with gusts to 45
kts. Periods of LLWS this morning as 1500-2000 ft winds of 45-50
kts. Winds gradually diminish after 09/00Z. Aviation discussion
not updated for TAF amendments.

&&

.FIRE WEATHER...

A low pressure system moving into the desert
southwest will result in much colder temperatures, breezy to
windy conditions, and chances for precipitation today. Although
precipitation amounts are expected to be light, isolated to
scattered rain and snow showers are possible with this low
pressure system lingering into Thursday, with some light snow
accumulations possible in valleys east of Tucson. After this
system departs, widespread sub-freezing temperatures are expected
across Southeast Arizona Thursday and Friday mornings. East to
southeast winds 20 to 30 mph with gusts 40-50 mph expected into
this evening. The colder temperatures will bring minimum relative
humidities into the 25 to 35 percent range today and Thursday,
then becoming drier again by this weekend.

&&

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 10 PM MST this evening for AZZ502>509-
511>515.

Freeze Warning from 10 PM this evening to 10 AM MST Thursday for
AZZ501>509.

Freeze Warning from 10 PM Thursday to 10 AM MST Friday for
AZZ501>509.

&&

$$

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