Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 190437

Area Forecast Discussion
National Weather Service Tucson AZ
937 PM MST Sun Feb 18 2018

.SYNOPSIS...Winter like conditions returns to southeast Arizona
this week as a couple of weather systems will bring gusty winds,
valley rain and mountain snow late tonight into Tuesday. Freezing
temperatures return to the lower elevations Tuesday night into
Wednesday morning from mainly Tucson east and south. Temperatures
will remain below normal through the end the week.


.DISCUSSION...The increasing southwesterly flow ahead of the main
trough currently digging through western states is on schedule
this evening accompanied by a moisture increase. The 00Z KTWC
sounding precipitable water was up to 3/4 of an inch with surface
dew points in the 40s. A weak inflection in the flow through
northwest Mexico and the Baja Peninsula assisted upslope effects
with enhanced training shower activity late in the afternoon and
early evening. Several training showers near far east Tucson into
the Rincon mountains generated 1/2 to 3/4 of an inch of rainfall,
but that was by far the heaviest area in the CWA. A few other
locations were in the 1/10 to 1/4 of an inch range, with main
emphasis on southwesterly facing slopes in mountain ranges. Snow
levels started out well above most of the terrain, around 9-10k
feet, and are still around 8-9k feet.

Minor updates earlier for latest analysis on 00Z model output for
first period and early second period. Please see the previous
discussion below for additional details.


.AVIATION...Valid thru 20/06Z.
BKN cloud layers with ceilings generally between 5-10k ft. Brief
MFR conditions possible with areas of valley -SHRA and mountain
SHSN. SFC wind W-SW 8-15 kts. SFC wind after 19/18z SW 15-30 kts
with ocnl gusts to 40 kts. Aviation discussion not updated for TAF


.FIRE WEATHER...There will be a chance of valley rain and
mountain snow showers tonight into Tuesday morning as a couple of
weather systems track through the desert southwest. The
associated strong trough will cause strong 20-foot winds Monday
out of the west blowing at 15-30 mph and gusts up to 40 mph,
mainly during the afternoon and into the evening in advance of a
strong cold front that will pass across the area later Monday
night. Dry and cooler conditions will follow the front Tuesday
through Thursday. Yet another weather system may bring a few
showers and breezy conditions on Friday.


.PREV DISCUSSION...As the upper level trough moves east tonight,
light shower activity will gradually increase in areal coverage.
The mountains will see increased shower activity over the next 12
hours as orographics take over as mid-level winds increase. The
cold front which extends from southern Nevada SW through the LA
Basin will move into western Pima county, be near Tucson by noon,
and then across Cochise county by late Monday afternoon. Showers
will continue across most of southeast Arizona on Monday with snow
level falling throughout the day. Will see a long period of light
to locally moderate snow starting later tonight and continuing
into late Monday night. Went ahead and issued a winter weather
advisory for elevations above 7500 feet for the Catalina, Rincon,
Pinaleno mountains for 4-8 inches and White Mountains for 6-12
inches. It will be rather gusty on Monday with the strongest winds
mainly east and south of Tucson where a wind advisory has been
posted. These gusty winds in the mountains will also produced
areas of blowing snow bringing about reduced visibilities.

Behind the system will be much colder air with highs on Tuesday
6-12 degrees colder than Monday. With a colder air mass in place,
overnight lows Wednesday morning will be quite cold with upper
10s and 20s in the colder eastern and southern valleys, and parts
of Tucson around freezing.

Remaining cool and dry Wednesday and Thursday as a pair of weak
upper level troughs pass thru the area. A deeper upper level trof
moves through the state on Friday. This system will bring a chance
of valley rain and mountain snow to the area.


Winter Weather Advisory until 5 AM MST Tuesday for AZZ510.

Wind Advisory from noon to 11 PM MST Monday for AZZ503>514.

Winter Weather Advisory until 11 PM MST Monday for AZZ511-514.




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