Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211135
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
435 AM MST Sat Jan 21 2017

.SYNOPSIS...Precipitation will decrease into this evening but gusty
winds will continue. Dry conditions will then prevail late tonight
into Sunday. A storm system moving north of the area will bring a
few showers Sunday night followed by more widespread valley rain and
mountain snow showers Monday and Monday night. Precipitation will
decrease Tuesday with dry conditions prevailing Wednesday into next
weekend.

&&

.DISCUSSION...Scattered valley rain and mountain snow showers were
ongoing generally from Tucson eastward to the New Mexico border at
this time. Otherwise, mostly cloudy to cloudy skies prevailed early
this morning along with gusty west winds. However, wind speeds as of
4 am MST were below wind advisory criteria.

Meanwhile, a deep upper low pressure system was centered just west
of the Pacific Northwest coast, and a trough axis extended
southeastward across the Great Basin and into southeastern Arizona.
The 21/00Z GFS/ECMWF were very similar with with shunting the deeper
moisture well eastward later today into the central/southern CONUS.
However, enough moisture should exist to support additional
accumulating snowfall across the mountains above 5000 feet east-to-
south of Tucson this morning. Otherwise, scattered to numerous
valley rain/mountain snow showers this morning will decrease in
coverage by this evening followed by dry conditions late tonight
into Sunday morning.

Thus, a Winter Storm Warning remains in effect until Noon MST today.
A tight mid-level gradient will also maintain gusty mainly west
winds today. Wind Advisories remain in effect until 5 pm MST this
afternoon for most locales east-to-south of Tucson. Please refer to
AWIPS products PHXWSWTWC /WMO Header WWUS45 KTWC/ and PHXNPWTWC /WMO
Header WWUS75 KTWC/ for additional information.

Moisture is expected to increase from northwest-to-southeast Sunday
afternoon into Monday as the aforementioned upper low pressure
system moves southeastward toward northern California. There is a
slight chance of showers Sunday afternoon west-to-north of Tucson,
then perhaps as far southeast as Tucson Sunday night. A chance of
valley rain and mountain snow exists Monday and especially Monday
night. A slight chance of valley rain/mountain snow continues
mainly from Tucson eastward Tuesday and Tuesday night.

A few snow showers may occur mainly across the White Mountains
Wednesday. Otherwise, a drying trend will commence by next
Wednesday, and markedly drier conditions will then prevail Thursday
into next Friday as high pressure aloft amplifies along the West
Coast.

High temps today will remain quite cool, and will average nearly 8-
15 degs or so below normal. A warming trend is on tap Sunday into
Monday, then much cooler temps will prevail Tuesday. Expect no
significant change in daytime temps Wednesday followed by high temps
returning closer to seasonal normals by next Friday.

&&

.AVIATION...Valid through 22/12Z.
Scattered to numerous -SHRA and higher terrain -SHSN today, then
isolated -SHRA and mountain -SHSN east of KTUS this evening. Dry
conditions area-wide late tonight into Sunday morning. Expect MVFR
conditions and occasional IFR conditions into this evening due to
precipitation. Otherwise, cloud decks mainly 3k-7k ft AGL today
followed by decreasing clouds tonight. Surface wind today mainly wly
12-25 kts with gusts of 25-40 kts. Surface wind diminishing to
mostly less than 12 kts most sections around 22/03Z and continuing
into Sunday morning. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Expect valley rain and mountain snow to decrease in
coverage into this evening followed by dry conditions late tonight
into Sunday morning. A slight chance of showers exists west-to-north
of Tucson Sunday afternoon and Sunday night, then scattered to
numerous valley rain and mountain snow showers will return Monday
and Monday night. Precipitation chances decrease again Tuesday with
dry conditions prevailing late Wednesday into next weekend. Gusty
west winds will occur today and again Monday afternoon. Otherwise,
20-foot winds will mainly be terrain driven less than 15 mph.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    Winter Storm Warning until noon MST today for AZZ510>515.

    Wind Advisory until noon MST today for AZZ503.

    Wind Advisory from noon today to 5 PM MST this afternoon for
      AZZ511>513.

    Wind Advisory until 5 PM MST this afternoon for AZZ507>509.

&&

$$

Francis

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