Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
858 AM MST Sat Aug 12 2017

.SYNOPSIS...Scattered to numerous thunderstorms will return this
weekend with heavy rain at times. 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...An area of upper level diffluence on the
northeast flank of the weak upper low just south of Organ Pipe
continues to fire morning convection through eastern Pinal and
western Graham county. This will cycle down over the next hour or
two as diurnal influences take over. The 12Z KTWC sounding was up
to 1.76 inches precipitable water. There's a subsidence inversion
around 400hPa that will work it's way down toward H5 during the
day, but we should easily reach a convective temperature to
overcome it. Plenty of instability and SB/MU convective potential.
Our shear is not the best so storm structure will struggle a
little. Also, as the weak low lifts into southwest and south
central Arizona, we will see a dry slot from the west wrap in
under it with some mid level drying in western areas. That will
be countered a little by a nice surge ongoing from the Gulf of
California into the lower deserts, last showing up as about 6k
feet deep on the KYUX VAD wind profile.

So what's the forecast? We're standing pat with an active 36 hour
period as another low approaches SE AZ from southern Sonora. We
may struggle out west though, and it will be tough to time in
decreasing storm trends from the west vis-a-vis Tucson Metro.

After a complicated weekend, the downward trend gets obvious next
week with the sustained westerly flow increasing as a trough digs
in north of the area.

&&

.AVIATION...Valid thru 13/18Z.
SCT-BKN clouds at 7k-11k ft AGL. Isolated to scattered -TSRA/-SHRA
mainly north to northeast of KTUS thru 12/17Z. Aft 12/17Z,
TSRA/SHRA becoming more numerous and widespread through the rest
of the morning and into the afternoon hours, slowly diminishing
aft 13/04Z. MVFR ceilings and visibilities near the stronger TSRA.
Strong and gusty outflow winds to 45 knots with the TSRA,
otherwise SFC winds generally less than 12 kts. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Scattered to numerous thunderstorms this weekend
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
next week. 20-foot winds will generally be terrain driven less
than 15 mph apart from gusty thunderstorms outflows.

&&

.PREV DISCUSSION...A weak upper low was positioned over the
northern Gulf of California and appeared to be helping showers
develop south of Lukeville in Sonora, Mexico and farther north
around Gila Bend. This feature should help focus showers and
thunderstorms across southeast Arizona today as it weakens and
tracks eastward over the area. Otherwise, elevated moisture will
support daily shower and thunderstorm activity again Sunday and
Monday. 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. That
said, will keep the downturn in thunderstorm activity in the
forecast with daytime readings remaining at or slightly above
normal.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

Meyer

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Special Weather Statement
National Weather Service Tucson AZ
103 PM MST SAT AUG 12 2017

AZZ507-513-122045-
Upper San Pedro River Valley including Sierra
Vista/Benson-Dragoon/Mule/Huachuca and Santa Rita Mountains including
Bisbee/Canelo Hills/Madera Canyon-
103 PM MST SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN COCHISE COUNTY UNTIL
145 PM MST...

At 102 PM MST, Doppler radar was tracking a strong thunderstorm near
southeastern Sierra Vista, moving east at 5 mph.

Half inch hail and winds in excess of 45 mph will be possible with
this storm, along with heavy rain.

Locations impacted include...
Sierra Vista, Hereford, Nicksville and Ramsey Canyon Preserve.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy rainfall is also occurring with this storm, and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3137 11036 3155 11042 3161 11024 3144 11013
TIME...MOT...LOC 2002Z 252DEG 5KT 3149 11031

Meyer