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fxus65 ktwc 172215 

Area forecast discussion
National Weather Service Tucson Arizona
315 PM MST Tue Sep 17 2019

Synopsis...isolated afternoon thunderstorms mainly near the
mountains east of Tucson through Thursday. Dry conditions this
weekend with the prospects of tropical moisture returning to the
area early next week. Seasonably warm daytime temperatures this


Discussion...a westerly flow under a regional trough is eating
away at our moisture with precipitable water values down to around
1 inch this afternoon. Surface dew points are mixing into the
40s, down 6 to 12 degrees compared to yesterday. Just some cu
fields so far, but a couple of quick storms still possible over
southeast mountains. As another trough sharpens and drops into
northern portions of the state we could see a little more dynamics
to work on the meager moisture for a few mountain thunderstorms
the next couple of days. More significant drying behind the
Thursday/Friday trough for a complete thunderstorm shut-down into
the weekend.

As we watch a transition season pattern set in right on schedule
with slowly deepening trough trajectories, the tropics are heating
up right on schedule too. Three named storms in the eastern North
Pacific with Kiko well out to sea and newly named Lorena and mario
just southwest of Mexico. A 4th area of interest just off the
coast of Central America. We need the trough trajectories to dig
far enough south to draw these storms further north and into play
for US. Otherwise a blocking ridge across northern Mexico will
tend to guide them further west before any turn to the north. Next
week could end up being very active as per gefs ensembles and an
increasing number of atcf members (18z run). The latest storm
track from the NHC takes Lorena toward southern baja Friday and
Saturday, in prime position to push deeper moisture our direction
late in the weekend and early next week. Lots of scenarios, but an
increasing number of them are leading to a strong moisture
increase with increasing storm chances in the late Sunday through
Wednesday time period.


Aviation...valid through 19/00z.
Slight chance of -tsra/-shra thru 18/04z and then again aft 18/18z
mainly east of a kols to ksad line. Otherwise, few-scattered clouds
(locally bkn) at 8k-12k ft mean sea level. Surface wind less than 12 kts and
variable in direction. Wind gusts near thunderstorms and rain to 35 knots. Aviation
discussion not updated for taf amendments.


Fire weather...there will be a slight chance of afternoon/early
evening showers and thunderstorms through Thursday mainly east and
south of Tucson. Dry conditions are expected Friday through the
upcoming weekend. A chance of showers and thunderstorms then returns
early next week. Seasonably warm daytime temperatures will occur
through this weekend. Aside from any thunderstorm wind gusts, 20-
foot winds will be terrain driven and less than 15 mph.


Twc watches/warnings/advisories...

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