Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 240930

Area Forecast Discussion
National Weather Service Tucson AZ
230 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...Dry and cool weather has settled into southeast
Arizona under dry west to northwest flow aloft. Even with clear
skies and abundant sunshine today, temperatures will struggle and
top off about 5 degrees below normal for this time of year. Another
clear and cold night tonight, then some moderation in temperatures
Saturday with highs near normal under dry zonal flow aloft.

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.


.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.





Aviation/Fire Weather...Francis

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