Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 122245

Area Forecast Discussion
National Weather Service Tucson AZ
345 PM MST Sun Feb 12 2017

.SYNOPSIS...A low pressure system will bring a chance of valley
rain, mountain snow and cooler temperatures into Monday. A slight
chance of showers continues Tuesday mainly from Tucson eastward,
then dry dry conditions with warmer temperatures Wednesday through
Friday. A chance of valley rain and mountain snow returns next


.DISCUSSION...Low pressure aloft was centered over northern Baja
California this afternoon. Meanwhile, a cold front had moved from
southwest New Mexico westward into far southeast Arizona. The
combination of strongly diffluent flow aloft, low level convergence,
and a marginally unstable environment has produced scattered
thunderstorms mostly east of a Safford to Bisbee line since around
noon. A few lightning strikes had also been detected since around 3
PM MST in the vicinity of the Tucson metro area, or particularly
near the Rincon Mountains and the Catalina Foothills.

The upper low is progged to turn northeastward and move into
southwest New Mexico Monday afternoon. 12/12Z NAM/GFS/ECMWF and
several high resolution models suggest that the greatest coverage of
valley rain/higher elevation snow showers will occur mostly from the
Tucson metro area eastward to the New Mexico border through Monday.
The models suggest that the best chance of measurable rainfall for
the Tucson metro area would occur early this evening, then again
Monday morning. A tightening mid-level gradient will also produce
gusty east to southeast winds into tonight. At this time, appears
that wind speeds will mostly remain below advisory criteria, but a
few locales may briefly experience wind advisory criteria.

Meanwhile, snow levels will remain fairly high as the upper low
moves just southeast of the area. Forecast snow amounts across the
White Mountains merited the issuance of a Winter Weather Advisory by
the midnight shift. Thus, the Winter Weather Advisory for snow
remains in effect for AZZ510 (White Mountains of Graham and Greenlee
Counties) from 8 PM this evening to 8 PM MST Monday above 8000 feet.

Precipitation is expected to decrease in coverage from west-to-east
Monday afternoon into Monday night as the upper low continues
eastward into West Texas. However, the 12Z NAM/GFS/ECMWF continue
with solutions similar to their respective solutions from 12 hours
ago regarding precip potential for Tuesday. A vort lobe behind the
departing upper low is progged to move southward across the area

This feature in combination with remnant moisture supports the
scenario of at least a slight chance of valley rain/mountain snow
showers mostly from Tucson eastward to the New Mexico border into
Tuesday evening. A few lingering valley rain/mountain snow showers
may continue late Tuesday night across far eastern sections. Dry
conditions will then prevail Wednesday into Friday.

Thereafter, the deterministic 12/12Z GFS/ECMWF were quite similar
with depicting a deepening upper trough/closed low near the
California Coast Friday night. The negatively-tilted upper trough is
progged to move eastward into western Arizona Saturday, then
continue eastward into the southern Rockies next Sunday. These
solutions as well as the recently received 12/18Z GFS suggest a wet
period in the offing next weekend. Thus, there is at least a slight
chance of showers area-wide Friday night, with chance-category PoPs
west of Tucson. A chance of valley rain/mountain snow showers exists
Saturday into next Sunday.

The cooling trend that started today will continue into Monday.
Expect no significant change in daytime temps Tuesday, then a daily
warming trend will prevail Wednesday into Thursday. Expect cooler
temperatures next weekend associated with the aforementioned upper


.AVIATION...Valid through 14/00Z.
SCT to NMRS -SHRA and higher terrain -SHSN will continue into Monday
afternoon. The greatest coverage should generally be from KTUS east
to the NM border. ISOLD -TSRA will also occur into this evening.
Otherwise, expect cloud decks around 7k-11k ft AGL into Monday.
ELY/SELY SFC wind into tonight at 10-20 kts with gusts of 20-35 kts.
The strongest speeds should occur near KDUG. Wind speeds will lessen
after 12Z Monday. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Expect scattered to numerous valley rain and
mountain snow showers tonight. A few thunderstorms may also occur
through this evening. Showers will gradually decrease from west-to-
east Monday, but scattered showers especially from Tucson eastward
will return Tuesday. Dry conditions will prevail Wednesday into
Friday followed by another shot at valley rain/mountain snow next
weekend. Gusty E or SE winds will occur this evening into Monday
morning and again Wednesday afternoon. Look for elevated SW winds on
Friday and Saturday. Otherwise, 20-foot winds will generally be less
than 15 mph.


   Winter Weather Advisory from 8 PM this evening to 8 PM MST
     Monday for AZZ510 above 8000 feet.




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