Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 271642

Area Forecast Discussion
National Weather Service Tucson AZ
942 AM MST Mon Feb 27 2017

.SYNOPSIS...A Pacific weather system will bring a few showers
west of Tucson this afternoon, then an increasing chance of
valley rain and mountain snow showers this evening into Tuesday.
Strong gusty winds will also develop today and Tuesday. Dry
conditions with a strong warming trend will return Wednesday into
next weekend.


.DISCUSSION...Increasing southwesterly flow this morning, just
ahead of a trough developing through Pacific states. An initial
impulse moving in from the west later today and tonight appears to
be slightly further north on current analysis, and latest model
output is starting to shear it a little further north than
previously expected. We updated the current forecast to diminish
precip chances this evening from Tucson southward. With the cooler
mid level air starting to move in, we also added a mention of
thunder to the weather grids west of Tucson and Sells (mainly
western Pima county). Finally, with winds increasing again this
afternoon, we added blowing dust to the forecast for problem areas
of northeast Cochise county, including I-10 east of Willcox.

Please see the previous discussion below for additional details
beyond today and tonight.


.AVIATION...Valid through 28/18Z.
Isolated -SHRA developing west of KTUS this afternoon followed
increasing valley -SHRA and mountain SHSN this evening into
Tuesday. The heaviest precipitation should occur north of KTUS.
Remaining mostly VFR, with occasional MVFR conditions possible
overnight into Tuesday morning. Surface wind becoming swly/wly
12-18 kts with gusts to 25 kts this afternoon into Tuesday
morning, increasing Tuesday afternoon. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...A fast moving Pacific weather system will bring a
slight chance of showers west of Tucson this afternoon. There is a
better chance of valley rain and mountain snow showers tonight
into Tuesday. The least favored area for significant precipitation
is southeast of Tucson. Dry conditions will prevail Tuesday night
into early next week. Expect gusty southwest to northwest winds
this afternoon into Tuesday. Thereafter, a generally light
easterly wind regime will prevail Wednesday through Friday
followed by normal diurnal wind trends next weekend.


.PREV DISCUSSION...The models continue to suggest that two main
periods for any valley rain/mountain snowfall of significance may
occur this evening and again Tuesday. The bulk of the heavier
valley rain/mountain snow totals should also occur north of
Tucson, while locales southeast of Tucson will be the least prone
areas for measurable precipitation.

As was the case 24 hours ago, snow levels by Tuesday afternoon are
forecast to range from 6000-6500 feet across the White Mountains to
near 7500 feet southeast of Tucson. Storm total valley liquid
amounts are projected to generally range from 0.10"-0.50", with
water equivalent in the mountains mainly from 0.40"-1.20". Expect
new snow accumulations of 6-10 inches above 6500 feet across the
Catalina/Rincon Mountains, Mt. Graham and the White Mountains.
Very minimal snow accumulations should occur elsewhere.

Another concern with this system will be gusty west to southwest
winds especially east of Tucson this afternoon and continuing into
Tuesday. These gusty winds may be produce localized blowing dust
restricting visibilities to less than one mile, as was case Sunday
afternoon along Interstate 10 near San Simon in northern Cochise
County. Travelers should remain alert to potentially rapidly
changing visibilities in this area.

Any precipitation is expected to end by Tuesday evening followed by
rapidly clearing skies from west to east. Thereafter, dry conditions
will prevail Wednesday into early next week. The 27/00Z deterministic
GFS/ECMWF were similar to previous solutions in depicting a weak
upper trough to develop well south of the area by this weekend.
However, progged moisture fields remain very dry through at least
Friday translating into clear skies or perhaps just a few clouds at
times Wednesday into Friday. Thereafter, periods of mostly cirriform
clouds should prevail this weekend.

High temps this afternoon will be a few degrees warmer versus Sunday
followed by about 2-8 degrees of cooling Tuesday. A strong warming
trend will occur Wednesday into the upcoming weekend, with high
temps Saturday and Sunday forecast to average mainly 10 degrees
above normal.


Winter Weather Advisory from 6 PM this evening to 5 PM MST
Tuesday for AZZ510-511-514.




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