Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 170345

Area Forecast Discussion
National Weather Service Tucson AZ
845 PM MST Sat Sep 16 2017

.SYNOPSIS...Isolated afternoon and evening thunderstorms mainly east
to south of Tucson during the upcoming week. Expect near normal high
temperatures through midweek followed by a cooling trend with breezy
to windy conditions especially Friday into next Saturday.


.DISCUSSION...Isolated showers and thunderstorms occurred this
afternoon and early this evening generally in an area bounded from
near Sasabe northeastward to the Rincon Mountains east of Tucson,
then southward to west of Sierra Vista. This area was characterized
with MLCAPEs around 500-700 J/kg as per SPC Mesoscale Analysis, and
the 17/00Z KTWC sounding MLCAPE of 492 J/kg and LI of minus 3. These
showers/tstms produced very little rainfall - mostly trace amounts -
and dissipated by 7:30 pm MST. Clear skies prevail at this time west
of Tucson with mostly clear skies from Tucson eastward to the New
Mexico border.

IR satellite imagery trends suggest that clouds will continue to
gradually dissipate across eastern sections during the next several
hours. Thus, expect clear skies to mostly clear skies the rest of
tonight with surface winds mainly less than 10 mph. Low temperatures
early Sunday morning will be quite close to seasonal normals, or a
few degrees above normal, depending upon location.

Please refer to the additional sections for further detail.


.AVIATION...Valid thru 18/06Z.
Isolated -TSRA/-SHRA east of KTUS Sunday afternoon and evening.
Otherwise, clear skies west of KTUS with a few to scattered clouds
around 8k-12k ft AGL east and south of KTUS. Surface wind variable
in direction mainly less than 12 kts into Sunday morning. Surface
wind Sunday afternoon and evening swly to nwly 10-18 kts with gusts
to 25 kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Expect isolated afternoon and evening thunderstorms
mainly east to south of Tucson during the upcoming week. 20-foot
winds will generally be terrain driven at less than 15 mph through
midweek. Thereafter, a cooling trend with breezy to windy conditions
should occur late next week as low pressure deepens north of the


.PREV DISCUSSION /205 PM MST/...A broad but fairly flat trough over
the western CONUS for much of the upcoming week will keep westerly
flow aloft across the area. We`ve been watching Hurricane Norma
situated to the south of the Baja peninsula which is expected to
weaken later this upcoming week off the western coast of the
southern Baja peninsula. It will be close enough to influence our
moisture, especially south and east of Tucson but the broader
westerly flow aloft this far north will keep the bulk of the
moisture to our south across Sonora. As moisture seeps northward
from time to time, there will be a slight chance of a shower or
thunderstorm especially for Cochise County with areas north and west
of Tucson expected to remain dry this upcoming week. As the
troughiness is fairly flat through midweek, heights will be a bit
higher than previously expected, so have bumped up temps upward a
few degrees Tuesday and Wednesday.

Medium range guidance is indicating a more amplified trough by
Friday and Saturday moving into the Desert Southwest which would
enhance the afternoon breezes and subsequently bring in more fall
like temperatures. As the trough moves in, there are some
differences on just how much moisture will lurk just to our south by
Friday and Saturday that can be advected north/northeast into areas
mainly from Tucson eastward. Played a middle of the road approach at
this time with slight chance PoPs east and south of Tucson.






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