Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 280352

Area Forecast Discussion
National Weather Service Tucson AZ
852 PM MST Mon Feb 27 2017

SYNOPSIS...A Pacific weather system will bring a chance of valley
rain and mountain snow showers into Tuesday. Strong gusty winds
will continue into Tuesday. Dry conditions with a strong warming
trend will return Wednesday into next weekend.


.DISCUSSION...A large area of steady showers continues across
areas to our west and north with a passing band of very light
showers having moved northeast through the Tucson area over the
last hour or so. Very little of significance across the lower
elevations with more enhanced precipitation across the mountains
where fairly strong upslope flow is doing its best to enhance the
precipitation. This will likely be the case through much of the
night as our immediate neck of the woods will need to await the
secondary impulse that will drive the front across the area on
Tuesday. Even then, not holding out much hope for much
precipitation across the lower elevations and potentially none SE
half of Cochise county. For now I made a few minor tweaks to
several of the forecast elements for the tonight into Tuesday
morning timeframe and sent a quick update.


AVIATION...Valid through 28/23Z.
Isolated to scattered valley -SHRA and mountain SHSN through the
first half of the night then becoming more numerous late tonight
and Tuesday. The heaviest precipitation should occur north of
KTUS. Cloud decks SCT-BKN 5k-8k ft AGL and BKN-OVC 10k-15k ft
AGL. Expect possible MVFR conditions late tonight and early
Tuesday. Surface wind sly/swly at 12-20 kts with gusts up to 28
kts thru 28/14Z. The strongest speeds will be east of KTUS in the
vicinity of KDUG, KALK and KSAD. Surface wind will increase after
28/14Z, with swly/wly surface wind at 16-26 kts and gusts to 35-40
kts, with the strongest speeds in the vicinity of KDUG, KALK and
KSAD. Aviation discussion not updated for TAF amendments.


FIRE WEATHER...A fast moving Pacific weather system will bring a
chance of valley rain and mountain snow showers late tonight and
Tuesday. The least favored area for significant precipitation is
southeast of Tucson. Dry conditions will prevail Tuesday night
into early next week. Expect gusty south to southwest 20-foot
winds through early Tuesday morning and strong and gusty southwest
to west winds from late Tuesday morning through the early evening
hours Tuesday. Thereafter, a generally light easterly wind regime
will prevail Wednesday through Friday followed by normal diurnal
wind trends next weekend.

At this time, critical fire weather thresholds are not expected to
be met on Tuesday. Although wind speeds will easily meet criteria,
increasing moisture will result in minimum relative humidity values
of only 20-25 percent over portions of Cochise and Graham counties
and higher values elsewhere.


.PREV DISCUSSION... /issued 254 PM MST Mon Feb 27 2017/

Our main weather story will be a trough of low pressure currently
consolidating immediately upstream through Pacific states. The
remains of the low previously off the California coast has been
co-opted into the base of the trough and is currently shearing
through Yuma county with showers increasing from the southwest
there. This area will spread east and north over the next 12
hours, and will be more of an impact for areas north of Tucson
tonight. Most shower activity south of Casa Grande will be light
to moderate this evening.

The front associated with the main part of the system will push
through from the west Tuesday, with shower activity increasing in
our area ahead of the front in the morning hours, before
diminishing behind the front Tuesday afternoon. Storm total valley
rainfall between .1 and .5 inches, with lighter amounts near
international border areas. Snow levels around 7k feet tonight,
then between 6k and 7k feet Tuesday. 5 to 10 inches above 6500
feet around the Mt Lemmon and Mt Graham areas, with 10 to 16
inches in the mountains of northern Graham and Greenlee counties
(southern portions of the White Mountains).

Clearing from the west late Tuesday. At that point we shift into a
pattern with much less potential for lower latitude energy.
Instead of trough/ridge/trough/ridge, we`ll be
ridge/flat/ridge/flat with dry conditions and above average
temperatures from Thursday through at least the first half of
next week.


Winter Weather Advisory until 5 PM MST Tuesday for AZZ511-514.

Winter Storm Warning until 5 PM MST Tuesday for AZZ510.




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