Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 182121
Area Forecast Discussion
National Weather Service Tucson AZ
221 PM MST Sat Feb 18 2017
.SYNOPSIS...A slow moving storm will continue to spread valley
showers and mountain snow across southern Arizona through Sunday
evening with blustery conditions into this evening. Dry and
quickly warming weather will return Monday through Wednesday
before a system passing to the north cools temperatures again
late in the week.
.DISCUSSION...The bulk of the precipitation thus far has occurred
well west of our area with over 2/3rds of an inch in Yuma through
noon. Elsewhere, scattered light showers with snow observed at
the highest peaks including Mt Lemmon where some light snow
appeared on web cams last hour. The area of precipitation over
Pima, Santa Cruz and western Cochise counties is expected to fill
in over the next few hours where low level convergence and upper
level divergence have come together as the system approaches. This
trend should continue into the evening hours. In the meantime it
has been rather breezy today with plenty of gusts well into the
30s and a few 40+ mph. That will also continue for a few more
hours before easing back.
By Sunday morning model consensus has the upper low near Casa
Grande and slowly shifting to the east as it opens up. This will
leave our area in a slightly unstable regime with breaks of
sunshine and scattered showers, more numerous over the mountains
and with lower snow levels should see snow showers down to around
6,000 ft with accumulations mostly limited to above 7,000 ft.
Current forecast of 10-16 inches for storm totals today though
Sunday evening above 7,500 ft may be a touch on the high side but
in the ballpark so won`t tweak significantly at this time.
If current timing holds the trough axis will be moving east of
the New Mexico border Sunday afternoon so would expect a general
decrease in the showers in the afternoon from west to east with a
rapid decrease after sunset with the loss of heating and a short
wave ridge quickly building in from the west. With some clouds,
scattered showers and cool air mass in place high temperatures
should peak a few degrees cooler than average for February 19th.
As mentioned, drying will kick in Sunday night with dry weather
expected through the coming week with the possible exception of a
stray shower northern areas as a system passes by to the north
Wednesday night. It will warm quickly Monday through Wednesday
with high temps around or a bit above 80 from Tucson westward
Tuesday and Wednesday. Temps will be forced back down to more
normal levels Thursday and Friday thanks to the previously
mentioned system passing by Wednesday night. There is some
suggestion of another system passing by or through the area late
next weekend. Time will tell how that plays out.
.AVIATION...Valid through 20/00Z.
SCT-NUMEROUS valley SHRA and higher terrain SHSN into Sunday. ISOLD
TSRA are possible for the remainder of this afternoon and early
evening, mainly from KTUS south and west. MVFR and occasional IFR
conditions possible in and near heavier pcpn. Cloud decks mainly
between 4-8k ft AGL. Gusty SLY/SELY SFC wind 15-25 kts with gusts of
35-40 kts possibly into early this evening. Speeds will lessen to
less than 15 kts late this evening into Sunday morning. SFC wind
Sunday generally SWLY at 8-12 kts with pcpn decreasing from west to
east throughout the day. Aviation discussion not updated for TAF
.FIRE WEATHER...Widespread valley rain and mountain snow will
continue into Sunday in association with a strong Pacific storm
system. Gusty south to southeast 20-foot winds will continue into
this evening, with speeds diminishing tonight. Expect some southwest
breeziness on Sunday as precip ends from west to east. Dry
conditions, a warming trend and normal diurnal wind patterns will
then occur Monday through the middle of next week.
Winter Storm Warning until 5 PM MST Sunday for AZZ510-511-514.
Wind Advisory until 4 PM MST this afternoon for AZZ502>504-507-
Winter Weather Advisory until 5 PM MST Sunday for AZZ512.
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