Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
932 AM MST Fri Jul 20 2018

.SYNOPSIS...Isolated to scattered thunderstorms today into Saturday.
As high pressure strengthens over the desert southwest late this
weekend into early next week, the number of storms will decrease and
temperatures will climb to well above normal with near record heat
possible early next week.

&&

.DISCUSSION...Another day and another round of thunderstorms.
Moisture levels today on par with yesterday as far as PW values go
with only slightly lower dewpoints. This has resulted in lower CAPE
values than yesterday but still in excess of 2000 this morning which
is more than enough. We have a triggering feature moving NW out of
Mexico which should help support convection with a couple of storms
now moving into the Douglas area. Should be a good afternoon and
evening convection wise with the setup that we have. No changes
needed to the short-term forecast. The heat next week is well
addressed in the previous discussion below.

&&

.AVIATION...Valid through 21/12Z.
A few TSRA nr KDUG this morning otherwise ISOLD-SCT TSRA today after
20/19z with cloud bases 8-10k ft AGL. Outside of strong and erratic
TSRA outflows, surface winds remain below 12 kts through the period.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to occasionally scattered afternoon and
evening storms are forecast today and Saturday. Heat will build
Sunday into early next week with potential for record high
temperatures. Outside of thunderstorms, 20-ft winds remain below
15 mph, although the Upper Gila River Valley will experience
gustier northwesterly winds at times.

&&

.PREV DISCUSSION... /issued 322 AM MST Fri Jul 20 2018/
Clear to partly cloudy sky prevailed this morning across southeast
Arizona. A weak upper level disturbance moving across northern
Chihuahua has kicked off a few thunderstorms southeast of the New
Mexico boot. May see a few of these storms move into far southeast
Cochise county around sunrise. Otherwise the above mentioned feature
will be the driver in storms today as it moves W-NW northern Sonora
and southern Arizona. Outflow interactions will keep storms going
into the late evening hours west of Tucson. Locally heavy rainers
with PW values in the 1.3" to 1.6" range.

Plenty of debris cloudiness Saturday will delay thunderstorm
development. Areal coverage down a bit compared to today due to the
clouds and warming temperatures aloft. Highs at or slightly warmer
than today.

Strengthening high pressure aloft along with continued warm mid-
level temperatures will limit thunderstorm coverage on Sunday to
mainly the high terrain.

Main weather story early next week will be the late July heat
wave with most areas below 5000 feet meeting heat warning
criteria both Monday and Tuesday with record or near record highs.
Based on coordination between the SW offices, went ahead and
upgraded the Excessive Heat Watch to Warning. Later shifts may
need to add Wednesday to the Warning along with the possibility of
warmer highs as model thickness values are warmer than current
forecast. Both EC/Canadian hinting that Tucson could approach July
all-time high either Tuesday or Wednesday. Still holding on to
some moisture for slight chance of mainly mountain storms early
next week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 10 AM Monday to 8 PM MST Tuesday for
AZZ501>509.

&&

PUBLIC...Cerniglia
AVIATION....Rasmussen
FIRE WEATHER...Rasmussen

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Special Weather Statement
National Weather Service Tucson AZ
1232 PM MST FRI JUL 20 2018

AZZ503-513-202015-
Dragoon/Mule/Huachuca and Santa Rita Mountains including
Bisbee/Canelo Hills/Madera Canyon-Upper Santa Cruz River and Altar
Valleys including Nogales-
1232 PM MST FRI JUL 20 2018

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN SANTA CRUZ COUNTY UNTIL
115 PM MST...

At 1229 PM MST, Doppler radar was tracking a strong thunderstorm 5
miles east of Patagonia, or 18 miles west of Sierra Vista, moving
west at 10 mph.

Winds in excess of 40 mph and pea-size hail will be possible with
this storm.

Locations impacted include...
Patagonia and southern Sonoita.

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 3154 11052 3142 11049 3142 11076 3167 11078
      3162 11060
TIME...MOT...LOC 1929Z 100DEG 10KT 3148 11060

JKP