Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 111619
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
919 AM MST Wed Jan 11 2017

.SYNOPSIS...Expect dry conditions with mild daytime temperatures
through Thursday. A low pressure system will then bring a chance
of valley rain and mountain snow over the weekend along with
cooler temperatures. Dry conditions with warmer temperatures will
return early next week. Another storm system may impact the area
later next week.

&&

.DISCUSSION...Our zonal flow is slowly starting to buckle as
energy carves down the west coast over the next 36-48 hours. Our
12z sounding showed layers of moisture above 700mb but not much
below that, with a total PW around .4 inches. Patches of mid and
high cloud at times with temperatures a few degrees above average.
We`ll continue to monitor trajectories with more ensemble members
taking the system a little further south into northern Sonora. Our
current forecast message looks solid for the upcoming system with
biggest impacts on Saturday and Sunday.

Please see the previous discussion below for additional details.

&&

.AVIATION...Valid through 12/12Z.
FEW-SCT clouds at 11-14k ft AGL and BKN-OVC clouds AOA 20k ft AGL
thru the forecast period. Surface wind generally less than 12 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions with a gradual daily cooling trend
expected through Thursday. A low pressure system will then move into
the region late in the week, resulting in a chance of valley rain
and mountain snow starting Friday and continuing through Sunday. Dry
conditions are expected to return Monday through Wednesday of next
week. 20-foot winds through much of the forecast period will be
terrain driven and less than 15 mph.

&&

.PREV DISCUSSION...The next weather maker, currently off the
Pacific NW coast, will be over central California Thursday
afternoon, off the southern California coast Friday morning and
then over northern Baja California late Friday afternoon.
Operational models and ensembles are in pretty good agreement with
this scenario. As moisture values start to increase could see a
few light showers develop in the far west late Thursday night into
early Friday morning with areal coverage of showers increasing
west and north of Tucson through Friday afternoon. As the upper
low moves east into NW Sonora MX on Saturday, showers will be
increasing in areal coverage across most of the forecast area.
Snow levels will be lowering into the 5500 to 6500 level late
Saturday afternoon. Models lift upper low NE into NM on Sunday
with potential for secondary system on back side of low keeping
scattered valley rain and mountain snow showers around most of the
day.

Current thinking for storm total snowfall amounts has 3-10 inches
above 7000 feet with valley QPF values ranging from 0.10" to 0.80".
Plenty uncertainty exists on amounts with GEFS ensemble members
showing wide range of amounts. Still plenty of time to massage these
numbers as the event draws closer.

Below normal highs for the weekend and Monday with cold overnight
lows Monday and Tuesday morning in wake of system.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Meyer

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