Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 272033
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
133 PM MST Sun Nov 27 2016

.SYNOPSIS...A fast moving storm system will bring a good chance of
valley rain and mountain snow mainly tonight, especially from Tucson
north and eastward with continued cool temperatures Monday. Another
disturbance will once again bring a chance of a few rain and snow
showers Monday night into Tuesday. Expect the coldest overnight lows
of the season so far Tuesday night and Wednesday night. Temperatures
will remain below average through the week, with another storm
system bringing a chance of valley rain and mountain snow Friday
into next weekend.

&&

.DISCUSSION...As the longwave trough has established itself across
the western CONUS, temperatures are below normal this afternoon
under partly to mostly sunny skies. The strongest shortwave
disturbance with this trough, now located near the southern Sierra
Nevada Mountains will rapidly swing southeast into Arizona this
evening and move through the area overnight. The best moisture and
dynamics will line up from Tucson north and eastward with a quick 3
to 6 hour period with a burst of precipitation possible. The
trajectory for this system is rather moisture starved, with about
.05" to .30" of QPF for valley locations from Tucson north and
eastward with even less SW of Tucson. However, favorable upslope
flow will enhance QPF in the mountains. Winds will also be gusty as
the system moves through tonight, especially in the higher terrain.
Snow levels will start at about 6,000 feet early this evening and
rapidly lower to 4,000 to 5,000 feet as the precipitation band moves
through the region. Any accumulating snow should remain above 5,000
feet with 3 to 6 inches possible above 7,000 feet from Tucson north
and eastward with perhaps a few higher amounts in the White
Mountains. The Winter Weather Advisory in effect starting at 6 PM
for the White Mountains which lines up with WFO Flagstaff nicely
looks good.

Most of the remaining precipitation should be east of our area by
sunrise Monday with the exception of perhaps a few upslope snow
showers in the White Mountains. Otherwise, dry and continued cool
conditions on Monday under northwesterly flow aloft. Another
slightly weaker disturbance will move through on the backside of the
trough Monday night into Tuesday. This system will also be moisture
starved but have increased PoPs this forecast cycle with a few rain
and higher elevation snow showers Monday night into Tuesday. Snow
levels will be down as low as 4000 feet in Graham/Greenlee Counties
and about 5000 feet in Cochise County. QPF looks meager with the
mountains perhaps seeing an inch or so of snow. Regardless, the
increased cloud cover will keep temperatures from crashing on Monday
night.

Conditions will improve as the day progresses on Tuesday for the
majority of the area with any leftover showers moving southeast out
of Cochise County during the afternoon. This will set the stage for
the coldest night of the season Tuesday night/Wednesday morning with
lows around freezing in the Tucson metro and a hard freeze for
locations south and east of Tucson. Brief flat ridging aloft will
move in Wednesday and linger into Thursday with dry conditions and
slightly warmer daytime temperatures. However, Thursday morning will
remain quite cold, though perhaps slightly warmer than Wednesday
morning.

Thereafter, continued cool with more active weather for Friday into
next weekend as an upper low gets cut-off from the main flow and
drops southward through the Great basin, into Arizona and then
possibly as far south as the Central Baja peninsula next weekend
before pushing eastward. There is still quite a bit of uncertainty
in both the deterministic and ensemble guidance this far out on the
amplitude and progressiveness of the system. Will continue to carry
slight chance to low end chance PoPs Friday through next weekend.

&&

.AVIATION...Valid through 29/00Z.
FEW-SCT clouds at 8-12k ft agl with SCT-BKN clouds at 15-20k ft agl
this afternoon, then becoming SCT-BKN 5-9k ft agl after 28/00Z thru
about 28/12Z then decreasing thereafter. ISOLD-SCT valley -
SHRA/mountain -SHSN developing this evening, becoming SCT-NUM after
28/04Z...then tapering off for eastern areas by 28/12Z. WLY/SWLY sfc
wind at 12-16 kts with occasional gusts to 25 kts. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Considerably cooler temperatures will prevail this
week. A weather system will result in widespread valley rain and
mountain snow tonight into early Monday morning. Generally dry
Monday with the exception of a few snow showers in the White
Mountains, then another chance of a few rain and snow showers Monday
night into Tuesday. Expect breezy west to southwest winds around 15
to 20 mph with higher gusts to continue into this evening. Some
residual westerly or northwesterly gustiness is possible mainly
across eastern zones Monday and Tuesday. A strong low pressure
system will bring another round of wintry weather and gusty east
winds to the region late in the work week into next weekend.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 6 AM MST
Monday for AZZ510.

&&

$$

GL

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