Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 170425

Area Forecast Discussion
National Weather Service Tucson AZ
925 PM MST Mon Jan 16 2017

.SYNOPSIS...Expect a few showers mainly near mountains into Tuesday
evening. Otherwise, dry conditions will prevail through Wednesday
night. A series of storm systems will then bring periods of valley
rain, mountain snow and gusty winds Thursday into early next week.
Some snow may occur to the valley floors east of Tucson by Saturday.


.DISCUSSION...IR satellite imagery depicted mostly clear skies
across western/central Pima County and south-central Pinal County
west-to-northwest of Tucson. Partly cloudy to mostly cloudy skies
prevailed east-to-south of Tucson, with the bulk of clouds near
mountains. 17/00Z KTWC sounding total precip water value of 0.54
inch was down nearly one-tenth of an inch versus 24 hours ago.
17/00Z upper air plots depicted a broad positive-tilted trough that
extended from the Upper Midwest CONUS southwestward into northern/
central Baja California. KTWC sounding measured winds in the surface-
300 mb layer were variable in direction mostly less than 15 kts.

17/00Z NAM/GFS and several HRRR solutions were very similar with
suggesting that precip-free conditions will occur across much of
southeast Arizona the rest of tonight and into about mid-morning
Tuesday. The GFS depicted that measurable rain Tuesday afternoon
would be mainly limited to near the New Mexico border. However, the
wetter NAM depicted that measurable rain or mountain snow Tuesday
afternoon would be markedly further west; or, as far as the Tucson
metro area as well as west of Nogales.

Based on these solutions, the official forecast of a slight chance
of mainly mountain snow showers into Tuesday morning followed by a
slight chance of valley rain/mountain snow as far west as Tucson
Tuesday afternoon appears very reasonable. The bulk of rain amounts
or snow accumulations will be quite light. High temps Tuesday are
forecast to be a few degs warmer versus this afternoon.

Please refer to the additional sections for further detail.


.AVIATION...Valid through 18/06Z.
Isolated -SHRA/-SHSN mainly near mountains into Tuesday evening.
Otherwise, west of KTUS expect FEW-SCT clouds around 5k-9k ft AGL
and SCT-BKN clouds above 20k ft AGL. KTUS vicinity eastward expect
SCT-OVC clouds around 4k-8k ft AGL and BKN-OVC clouds above 20k ft
AGL. Surface wind will be variable in direction mostly less than
10 kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Expect a few showers producing very light rain or
snow amounts mainly near mountains east and south of Tucson into
Tuesday evening. Otherwise, dry conditions will prevail into
Wednesday night. A series of Pacific storm systems will then bring
periods of valley rain, mountain snow and gusty winds Thursday into
early next week.


.PREV DISCUSSION...For Tuesday the weak upper level low will linger
near the NM border through the day and the associated weak
instability and low level moisture will maintain a small threat of a
few showers east of Tucson, primarily over higher terrain. With a bit
more sunshine the afternoon temperatures will end up 3-6 degrees
warmer than today. The pesky upper low will finally move off to the
east Wednesday but only because an approaching system will give it a
nudge. So we should have a mostly sunny and seasonably mild

The system responsible for the nudge will move into NW AZ later
Thursday and with the somewhat northern trajectory across the state
we will be on the drier side so not expecting a lot in the way of
precipitation late Thursday and Thursday night. Good for low chance
pops south and slightly higher White mountains.

However this system is the door opener for a stronger and wetter
system Friday through Saturday. This looks like it has the potential
for a decent shot of precipitation with fairly low snow levels Friday
night into Saturday, potentially affecting the higher valleys east of
Tucson by Saturday morning. This should be a vigorous system and it
will be interesting to see how it plays out. Back to colder than
normal Friday into Sunday with the colder air moving into the region.

This will be followed by a dry Sunday and possibly Monday, but
Monday is a bit up in the air at this point. Longer range models
continue to suggest another system impacting the area early to the
middle part of next week in some form or fashion. Overall, an active
week+ expected.





Previous Discussion...Cerniglia

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