Scientific Forecaster Discussion
fxus65 ktwc 180435
Area forecast discussion
National Weather Service Tucson Arizona
935 PM MST sun Dec 17 2017
Synopsis...valley rain and mountain snow showers associated with
slow moving low pressure south of Arizona will gradually dissipate
overnight as the low moves east. Wraparound moisture will allow
for some lingering mountain snow showers east of Tucson on Monday,
but drier air will move into the area through mid week. A trough
will sweep through The Four Corners late in the week bringing
increased cloud cover and cooler temperatures, but at this time it
doesn't look to bring much in the way of precipitation. Cooler
temperatures will linger through next weekend.
Discussion...water vapor imagery this evening showed the upper
low which bought valley rain and mountain snow to the area today
was located over far northwest Sonora Mexico or south of central Pima
County. Areal coverage of showers has decreased over the last
several hours with the exception along the international border,
or across Santa Cruz and southern Cochise counties. As the upper
low continues to slowly move east tonight, the last good slug of
moisture over eastern Sonora Mexico will move into Cochise County
with the Chiricahua Mountains seeing accumulating snows into early
Monday morning. Thus have extended the Winter Weather Advisory
for the Chiricahua Mountains until 2 am. The Winter Weather Advisory
for the rest of the mountain ranges was cancelled although will
still see isolated showers and mountain snow showers continue
through the overnight hours into Monday morning.
Aviation...valid thru 19/00z.
An upper level low pressure system over northwest Sonora Mexico
will continue to move east across the area thru the valid period.
Expect isolated to scattered valley rain and mountain snow
showers to continue into Monday. MVFR cigs/vsbys will
occasionally accompany the rain showers especially near terrain and east
of Tucson. Winds mainly southeasterly at around 8 to 12 kts.
Aviation discussion not updated for taf amendments.
Fire weather...low pressure will bring much higher relative
humidity and scattered precipitation to the area through Monday.
East to southeast winds this afternoon will give way to relatively
light/diurnally driven winds during through midweek. Once the
current weather system moves to the east, expect dry weather the
remainder of the week. As a weather system approaches Thursday,
expect some increased breezes. The bulk of this system will pass to
our north, thus dry and cool weather to end the work week and into
Winter Weather Advisory until 2 am MST Monday for azz512.