Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 241631
Area Forecast Discussion
National Weather Service Tucson AZ
930 AM MST Fri Feb 24 2017
.SYNOPSIS...Dry conditions will prevail through Saturday along with
cooler temperatures. A brief warmup on Saturday before a fast moving
system pushes across the area on Sunday. A stronger Pacific storm
will bring a chance of valley rain and mountain snow to the area on
Monday and Tuesday along with below normal temperatures. Dry and
warmer weather returns starting Wednesday.
.DISCUSSION...A chilly low morning will lead to a cool late February
afternoon across southeast Arizona under lots of sunshine. 12z
Tucson sounding showed considerable cooling below 700 mb versus 24
hours ago with 9 am temperatures running 5-12 degrees cooler. Latest
high resolution hourly temperatures are running a few degrees cooler
than what the official forecast has. At this time will not make any
changes to the forecast. Another chilly night with slightly warmer
highs on Saturday under zonal flow aloft.
.AVIATION...Valid through 25/12Z.
Clear skies to scattered clouds above 20k ft AGL into Saturday
morning. Surface wind this afternoon and early this evening nwly 8-
18 kts. Gusts of 20-30 kts should occur east of KTUS and especially
in the vicinity of KDUG and KSAD. Otherwise, surface wind will be
variable in direction less than 12 kts. Aviation discussion not
updated for TAF amendments.
.FIRE WEATHER...Dry conditions will prevail across much of the area
through Sunday night. The exception will be a chance of snow showers
mainly across the White Mountains Sunday. A Pacific system will then
bring a chance of valley rain and mountain snow showers, especially
Monday night into Tuesday. Dry conditions will return next Wednesday
and Thursday. Expect occasionally gusty west to northwest winds
during the afternoon hours primarily east of Tucson through Tuesday.
20-foot winds will be light and terrain driven next Wednesday, then
east winds mainly less than 15 mph next Thursday.
.PREV DISCUSSION...The next weather maker will be a weak shortwave
trough that will pass to our north on Sunday. The bulk of the
moisture and lift will remain to the north of this forecast area,
but we can`t rule out a slight chance of a rain or mountain snow
shower mainly northeast of Tucson. Elsewhere, some sprinkles are
possible but it will be a struggle to have much more than that with
a dry sub-cloud layer below 700 mb. Otherwise, this system will drop
high temperatures about 5 degrees on Sunday compared to Saturday.
A brief break Sunday night before the next trough moves into the
region Monday into Tuesday. The 00Z deterministic GFS/ECMWF/CMC have
backed off somewhat on the amplitude of the trough as it moves
through. However, there will still be considerable moisture with it,
which will result in a chance of valley rain and mountain snow
showers as early as Monday, but more likely Monday night into
Tuesday. QPF values aren`t looking too impressive at this time with
valley locations at less than 0.25" with perhaps 0.25"-0.50" in the
mountains, especially from Tucson north and eastward. This would
translate into the potential for about 3-6" of snow for the
mountains with snow levels averaging about 6000-7000 feet.
Meanwhile, this system will keep temperatures below normal as well
Monday and Tuesday. Drier weather is expected to return starting on
Wednesday with moderating temperatures.
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