Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 131613

Area Forecast Discussion
National Weather Service Tucson AZ
915 AM MST Sun Aug 13 2017

.SYNOPSIS...A good chance of showers and thunderstorms continues
into this evening. Some storms will generate heavy rain and strong
winds. A drying trend will begin Monday and continue during the
upcoming week, with only isolated thunderstorms mainly east to south
of Tucson by mid week.


.DISCUSSION...A rather busy night last night with significant rains
thanks to plenty of slow moving thunderstorm activity. Plenty of 1+
inch reports with a fairly large number of 2+ inch rain amounts.
Since then skies cleared nicely with warming getting underway
although it is starting from a fairly low bar.  We were unable to
launch a 12Z sounding due to convection overhead, but we are hoping
to launch one for 18Z to see how much potential remains in the
atmosphere today for afternoon and evening convection.  GPS and
GOES16 PW indicates about 1.6" across much of the area and to the
west with a dry hole to the south over Nogales with 1.1".

Some of the CAM guidance suggests redevelopment rather early today
with plenty of convection with others holding it off and
significantly less coverage.  Any larger scale forcing that I can
find appears to be over or a bit east of Tucson at the moment
leaving us to deal with solar initiation from roughly here westward.
Also there is a fairly significant moisture gradient in the water
vapor imagery bisecting the area from NW-SE which is also a favored
area to initiate convection and that will be over eastern areas.
this afternoon.  The upshot to all of that is that we stand a decent
chance of storms from just west of Tucson east to the border with
the best bet east of Tucson this afternoon where forcing will be an

Thereafter, models continued to show a deepening westerly flow
around Tuesday through next weekend. This will result in a drier and
less favorable pattern for daily thunderstorms, with daytime
readings remaining at or slightly above normal.


.AVIATION...Valid thru 14/18Z.
Redevelopment of isolated to Scattered -TSRA/-SHRA late this morning
and continuing through into the evening with SCT-BKN layers 6-10k ft
with a few layers above after 13/20Z. Brief wind gusts to around 40
kts and small hail with the stronger thunderstorms. Otherwise,
surface wind variable in direction mainly less than 12 kts. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...A good chance of thunderstorms today, followed by a
decrease in thunderstorms from west-to-east Monday into next Friday.
Isolated afternoon and evening thunderstorms will likely be limited
to locales east-to-south of Tucson most of the upcoming next week.
20-foot winds will generally be terrain driven less than 15 mph
apart from gusty thunderstorms outflows.





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