Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 260416
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
916 PM MST Sat Feb 25 2017

.SYNOPSIS...Dry conditions through tonight followed by a few
showers mainly north of Tucson Sunday. A Pacific weather system
will then bring a good chance of valley rain and mountain snow
showers by Tuesday. Below average daytime temperatures will
continue into Tuesday before dry conditions and a strong warming
trend kick in late next week.

&&

.DISCUSSION...Moderately strong westerly flow aloft as noted in the
evening sounding with the dry air firmly entrenched over the region
below 500 mbs (~18,000 ft MSL). Above that, high level moisture is
beginning to move in from the west in advance of a slowly approaching
system that is currently off the central California coast. This
moisture, readily apparent in the approaching cloud cover, will
increase and lower through the night into Sunday resulting in plenty
of cloud cover and just maybe a few showers well to the north over
the higher terrain. All these trends covered well in the current
forecast and other than tweaking temps and dewpoints a bit to account
for current trends left the current forecast as it was.

&&

AVIATION...Valid through 26/23Z.
Increasing high clouds above 15k ft AGL thru Sunday morning. Aft
26/15Z, FEW-SCT clouds at 7-11k ft AGL and SCT-BKN clouds at 11-15k
ft AGL. Surface wind less than 12 kts until 26/16Z then increasing
to swly/wly at 14-24 kts and gusts to 22-32 kts by 26/18Z. The
strongest wind will be in the vicinity of KDUG, KSAD and KALK.
Aviation discussion not updated for TAF amendments.

&&

FIRE WEATHER...Expect dry conditions through tonight, followed by
isolated to scattered showers northeast of Tucson Sunday. Dry
conditions will prevail in most sections Sunday night into Monday
morning. A Pacific weather system will then bring a slight chance of
showers Monday afternoon, with a good chance of valley rain and
mountain snow showers Monday night into Tuesday. Dry conditions will
prevail Wednesday into next Friday. The most significant winds will
occur Sunday and Tuesday, with the strongest winds expected southeast
of Tucson. Markedly less wind is on tap Wednesday, before some gusty
east winds occur Thursday and next Friday.

Critical fire weather thresholds may be met in a few isolated
locations for an hour or two Sunday afternoon across the southern
half of Cochise county. Although winds speeds will easily exceed
criteria, minimum relative humidity values will remain elevated,
bottoming out in the upper teens. Fire danger is also marginal, with
most locations still in the moderate rating.

&&

.PREV DISCUSSION... /issued 246 PM MST Sat Feb 25 2017/

DISCUSSION...Mostly clear skies across Southeast Arizona, with a
dry zonal flow in between systems. Precipitable water under 1/5 of
an inch on the 12z KTWC sounding, and surface dew points have
cratered into the single digits (or lower) across most of the area
this afternoon. The below average temperatures left behind by the
last system will moderate a bit over the next 48 hours.

A weak impulse passing just north of our area will keep
temperatures below average on Sunday, but most precip will remain
north of us. The biggest impact for our area will be the resulting
windy conditions. It may approach advisory levels in portions of
mainly Cochise County.

A bigger weather maker will visit the Desert Southwest early in
the new work week. A system currently well off the northern
California coast will phase with a stronger system currently near
the Pacific Northwest to create a new mean trough position through
western states Monday. It will have access to a fairly long fetch
of moisture from the Central Pacific to work with as it pushes
through our area Monday night and Tuesday. Best combination of
dynamics and moisture will be just ahead of and associated with
the frontal passage Tuesday. Not a terribly efficient or overly wet
system, with a 24 to 36 hour total of 1/4 to 1/3 of an inch in
valleys and 1/3 to 3/4 of an inch precip equivalent in mountains.
Maybe 4 to 8 inches of snow above 7000 feet, so we may need an
advisory. Gusty winds again an issue Monday afternoon into
Tuesday.

Height and thickness increases in the wake of the system with a
large scale ridge building through western states (even if there
may be a modest weakness in the flow near our latitude off the
eastern Pacific), will bring a strong warming trend the rest of
next week. Temperatures well above climate normals by Friday and
Saturday.

&&

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

$$

PUBLIC...Cerniglia/Meyer
AVIATION....Zell
FIRE WEATHER...Zell

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