Dust Storm in Arizona, February 26 to 28, 2017

Area Forecast Discussion
National Weather Service Tucson AZ
956 AM MST Sun Feb 26 2017

.SYNOPSIS...A weak disturbance will bring a chance of showers
northeast of Tucson today. A stronger weather system will then bring
a good chance of valley rain and mountain snow showers Monday night
into Tuesday. Below average daytime temperatures will continue into
Tuesday, then dry conditions with a strong warming trend Wednesday
into next Saturday.

&&

.DISCUSSION...A weak shortwave is creating variable cloudiness
along with a few sprinkles in valleys and snow showers in the
mountains northeast of Tucson. Might see a quick inch or so in
northern Graham and Greenlee counties above 6000 feet. Gusty winds
this afternoon but generally below advisory levels.

We're still on track for a stronger and wetter system late Monday
into Tuesday. A quick look at 12z analysis and latest model runs
show consistency with expected valley rain and mountain snow
locations as well as timing when compared to the forecast. We may
bring up precip amounts a little more. This is also still
consistent with advisory level snow amounts above 6500 feet, so we
went ahead and put that out for mountain ranges near Tucson
northward (Mt Lemmon area, Mt Graham area, and southern portions
of the White Mountains in northern Graham and Greenlee counties).

Please see the previous discussion below for additional details.

&&

.AVIATION...Valid through 27/18Z.
Isolated valley -SHRA and mountain -SHSN northeast of KTUS today.
Otherwise, cloud decks generally 8k-12k ft AGL today, then FEW-
SCT clouds around 10k-15k ft AGL this evening into Monday morning.
Surface wind this afternoon wly/nwly 10-20 kts with gusts up to
35 kts. The strongest speeds in vicinity of KDUG, and sustained
speeds around 25 kts may briefly occur. Surface wind variable in
direction less than 12 kts at other times. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered valley rain and mountain snow
showers northeast of Tucson today. Critical fire weather thresholds
may also briefly occur this afternoon near Douglas to the New Mexico
border. Dry conditions with less wind will then occur this evening
into Monday morning. A Pacific weather system will then bring a
slight chance of showers Monday afternoon followed by a good chance
of valley rain and mountain snow showers Monday night into Tuesday.
Dry conditions will return Tuesday night and continue into next
Saturday. Gusty winds will accompany the precipitation Tuesday
before less wind occurs Wednesday. Expect occasionally gusty east
winds Thursday and Friday.

&&

.PREV DISCUSSION...The broad scale upper trough continues to be
progged to deepen over the Great Basin and California Monday.
There is a slight chance of showers Monday afternoon well west of
Tucson. Precipitation will increase significantly starting Monday
evening and continuing into Tuesday as the upper trough moves
eastward across Arizona.

Have noted that the deterministic GFS/ECMWF were fairly similar with
attempting to depict two somewhat distinct periods for valley rain/
mountain snow to occur. The first period appears to be Monday
evening before a potential break in widespread precip occurs late
Monday night into early Tuesday morning. The second period of
heavier precip is then progged to prevail late Tuesday morning into
Tuesday afternoon. At least, from a numerical weather prediction
model perspective...

At any rate, there is a chance of valley rain/mountain snow showers
across much of the area Monday evening. There is only a slight
chance of showers southeast of Tucson Monday evening. Precip chances
increase markedly by Tuesday, and have attempted to depict the
highest precip chances generally from Tucson northeastward into the
White Mountains. Any measurable precip should end by Tuesday evening
followed by rapid clearing late Tuesday night.

Snow levels by Tuesday afternoon are now projected to range from
6000-6500 feet across the White Mountains to near 7000 feet
southeast of Tucson. Storm total liquid amounts now generally range
from 0.10"-0.50" in the valleys - perhaps just a few hundredths of
inch well southeast of Tucson. New snow accumulations of 5-9 inches
above 7000 feet are forecast to occur across the Catalina/Rincon
Mountains, Mt. Graham and the White Mountains. Subsequent forecasts
with at least these totals may prompt a Winter Weather Advisory for
snow issuance. Very minimal snow accumulations should occur
elsewhere.

Thereafter, dry conditions with a strong warming trend is on tap
Wednesday into next Saturday. The GFS/ECMWF continue with the
scenario of developing a weak upper trough well south of the area
next Friday-Saturday, but the progged moisture fields remain very
dry across this forecast area.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM Monday to 5 PM MST Tuesday for
AZZ510-511-514.

&&

Meyer/Francis

Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson