Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 192138

Area Forecast Discussion
National Weather Service Tucson AZ
235 PM MST Sun Feb 19 2017

.SYNOPSIS...A chance of valley rain and mountain snow will continue
into this evening. Dry conditions will occur Monday into next
Saturday except for a few snow showers across the White Mountains
Wednesday night and Thursday. Expect a sharp warming trend into
Wednesday with cooler temperatures late in the upcoming week.


.DISCUSSION...Partly sunny to mostly cloudy conditions this
afternoon across the CWA with scattered valley rain and mountain
snow showers. Cool surface temperatures as of 19/21z with values
around 7 to 10 degs below normal. WSW products continue to be in
effect until 20/00z this evening for elevations above 7500 ft as
some of the remaining precip could produce an additional couple
inches of snowfall this afternoon. Additional liquid amounts will
generally remain less than 0.15".

This storm system will continue to lift off to the northeast
overnight into Monday. We will see precip dwindle this evening and
end from southwest to northeast, with dry conditions occurring
tomorrow. Strong ridging setting up behind the low will cue a sharp
warming trend into Tuesday and Wednesday, when daytime high temps
will reach 7 to 10 degs above normal. Thereafter, models continue to
show varying forms of a shortwave trough digging south out of the
Pac NW and through the Great Basin. The latest operational solutions
indicate just a glancing blow for southeast AZ, as the trough axis
passes through the northern half of the state Wednesday night into
Thursday. With a tight pressure gradient aloft, expect to have some
gusty west winds Thursday afternoon, especially near the AZ/NM
border. Have also opted to continue with a slight chance for a rain
or snow shower across the White Mountains Wednesday night and

That system is a quick one, and will be out of here Thursday night.
Zonal flow sets up Friday into Saturday with daytime temps hovering
within a couple degrees of normal. In the extended, there are early
indications of another disturbance pushing through the region Sunday
and Monday. However, significant differences remain in timing and
intensity between the GFS/ECMWF, with the GFS stronger/wetter and
the ECMWF almost totally dry. Another situation where we will have
to wait and see what subsequent model runs have to say, but for now
have included at least a slight chance of precip for most areas
Sunday and Sunday night.


.AVIATION...Valid through 21/00Z.
Scattered valley -SHRA and mountain SHSN will diminish this evening
and end overnight with slowly clearing skies from the west. Cloud
decks will generally be 4k-8k ft AGL, but occasional MVFR
ceilings/visibilities will accompany showers thru 20/05Z. There is a
chance for some late night and early morning patchy valley fog
mainly south of Tucson, otherwise mostly clear skies expected
Monday. Surface wind will be sly/swly at 8-13 kts with gusts to 20
kts thru 20/02Z, then surface wind will generally be variable less
than 10 kts thru 20/19z then becoming NW 6-12 kts. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Scattered showers will come to an end tonight with
dry and warmer weather returning Monday through Wednesday. Then a
storm system passing across northern Arizona will bring breezy
conditions late Wednesday through Thursday with cooler temperatures
Thursday onward. There is a slight chance of a shower or two across
the northern mountains as this system passes. Then quiet, seasonal
conditions return Friday and Saturday. There is a chance for another
weather system to affect the area late next weekend.


    Winter Storm Warning until 5 PM MST today for AZZ510-511-
      513-514 above 7500 feet.

    Winter Weather Advisory until 5 PM MST today for AZZ512
      above 7500 feet.




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