Scientific Forecaster Discussion
fxus65 ktwc 271035
Area forecast discussion
National Weather Service Tucson Arizona
335 am MST Mon Feb 27 2017
Synopsis...a Pacific weather system will move rapidly eastward
across the area tonight and Tuesday. This system will bring a few
showers west of Tucson this afternoon, then a good chance of valley
rain and mountain snow showers this evening into Tuesday. Any
precipitation will end Tuesday evening followed by dry conditions
with a strong warming trend Wednesday into next weekend.
Discussion...upper level trough was deepening over the Pacific
northwest and Great Basin early this morning, with water vapor
satellite imagery depicting a darkening signature representing a
speed Max approaching the northern California coast. Based on the
27/00z NAM/GFS/ECMWF/CMC as well as the 27/00z univ of Arizona WRF-NAM
and WRF-GFS, there were only very minor changes made to the official
Thus, dry conditions to continue area-wide this morning but clouds
will increase quickly from west-to-east by midday. There is a chance
of showers west of Tucson this afternoon, then scattered to numerous
showers will occur this evening into Tuesday. 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/European model (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
Aviation...valid through 28/12z.
Isolated -shra developing west of ktus this afternoon followed by
scattered to numerous valley -shra and mountain shsn this evening
into Tuesday. The heaviest precipitation should occur north of ktus.
Expect MVFR conditions this evening into Tuesday morning. Otherwise,
mostly clear skies early this morning, then cloud decks lowering to
around 4k-8k ft above ground level this evening and continuing into Tuesday.
Surface wind mainly less than 10 kts this morning, then swly/wly 12-
18 kts with gusts to 25 kts this afternoon into Tuesday morning.
Expect precipitation to end with clearing skies after this forecast
period, or by Tuesday evening. Aviation discussion not updated for
Fire weather...a fast moving Pacific weather system will bring a
slight chance of showers west of Tucson this afternoon. There is a
good 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.
Winter Weather Advisory from 6 PM this evening to 5 PM MST
Tuesday for azz510-511-514 above 6500 feet.