Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 200414

Area Forecast Discussion
National Weather Service Tucson AZ
914 PM MST Mon Feb 19 2018

.SYNOPSIS...Winter returns to southeast Arizona this week as a
couple of weather systems will bring gusty winds, valley rain and
mountain snow 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 with another chance of showers Friday.


.DISCUSSION...The cold front associated with the winter storm
pushing through the region is making it`s way through Tucson at 9
PM, with shower activity enhancing immediately ahead of and with
it. Snow levels are falling rapidly behind the front. We`ve been
around 9k feet in the warm sector ahead of the storm, now falling
quickly to 7k feet with the front and plunging as low as 3500 to
4k feet within a few hours after frontal passage. We`re still
expecting 2 or 3 inches in the mountains with isolated higher
amounts possible above 8k feet. The most vigorous shower activity
will shift quickly east of the area over the next couple of hours,
but spotty weak low topped showers will continue behind the front
until the drier air pushes in from the northwest in the morning
hours. It will take a few hours to get here, but notice the
surface moisture gradient as per this hour`s dew points: Tucson
42, Casa Grande 26, Phoenix 2. The strongest winds just ahead of
and with the front are working out well, with our Wind Advisory
still in effect until 11 PM MST for areas primarily east of
Tucson. We made some timing and precip adjustments based on latest
analysis and model output to reflect these issues, but the
previous forecast already had things pretty well handled. Please
see the previous discussion below for additional details.


.AVIATION...Valid thru 21/06Z. SCT-BKN cloud layers with ceilings
generally between 4-8k ft. Isolated to scattered valley -SHRA and
MTN -SHSN mainly to the south and east of KTUS as a cold front
passes through this evening. Brief MVFR conditions possible
in/near -SHRA/-SHSN. SFC wind southwesterly/westerly at 18-28 kts
with gusts between 30-40 kts until around midnight. The strongest
speeds are expected at the KFHU/KDUG terminals. After midnight
winds will start to gradually decrease with speeds between 8-12
kts at KTUS and KOLS. KDUG will remain slightly elevated with
southwest winds at 12-17 kts and gusts between 25-30 kts after
midnight into Tuesday afternoon. Aviation discussion not updated
for TAF amendments.


.FIRE WEATHER...Isolated to scattered valley rain and mountain snow
showers will continue into Tuesday morning as a couple of weather
systems track through the southwest. Dry conditions and well below
normal temperatures will then occur Tuesday into Sunday morning,
with a few showers possible Friday afternoon. 20-ft southwest winds
will be gusty this afternoon, generally 20-30 mph with gusts up to
40 mph. Wind speeds will generally remain less than 15 mph Tuesday
and Wednesday. Slightly elevated west or southwest winds may then
occur late in the work week.


.PREV DISCUSSION...A much colder airmass across the area on
Tuesday with highs running 14 to 18 degrees below normal. Then
much colder overnight lows Tuesday night into Wednesday morning
with freezing temperatures likely from Tucson east and south. A
weak upper level trof moving across the area may bring enough
clouds to keep temperatures from realizing full cold potential. As
the above mentioned trof moves east across the area on Wednesday
it may have enough dynamics to work on residual moisture that will
be near the Arizona/New Mexico border to generate isolated light
valley showers and mountain snow showers. Increased PoPs a bit for
the Whites Wednesday afternoon and evening. Little snow
accumulation expected up there.

Another weak upper level trof moves across the area on Thursday in
advance of a deep upper level trof that will move across the state
on Friday. This deeper/colder upper level trof is being handled
differently by the models with the GFS deeper/colder than the more
progressive and not a deep ECMWF. For now went with a blend
between the models with gusty southwest winds a given. Could see a
scenario and showers will be associated with the cold front moving
across the area. Confidence low at this time.

Dry next weekend with a warming trend to near normal. Temperatures
for the remainder of the week into next weekend will be pleasantly
below normal. Love it.


Winter Weather Advisory until 5 AM MST Tuesday for AZZ510.

Wind Advisory until 11 PM MST this evening for AZZ503>514.

Winter Weather Advisory until 11 PM MST this evening for AZZ511.




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