Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
250 PM MST Mon Sep 23 2019

.SYNOPSIS...Showers and scattered thunderstorms will develop across
the area overnight and continue through much of Tuesday with local
severe storms possible through the evening. Local areas of heavy
rain is expected late tonight through Tuesday morning with local
flooding possible. After a break in the rain late Tuesday into early
Wednesday another round of potentially heavy rain is possible late
Wednesday into Wednesday night. Drier weather is then forecast this
weekend.

&&

.DISCUSSION...We currently have an air mass over the forecast that is
primed and ready for convection with abundant, high levels of
moisture, instability and wind shear. Despite this, the convection
across our area is rather lazy at the moment. Current mesoanalysis
shows the upper level forcing that is needed to make use of this
energy remains to our north leaving our area in area of unfavorable
vertical motion. However, that area of lift is expected to sag to the
south through the evening hours bringing about the threat for
thunderstorm development this evening. Will also be watching outflow
boundaries moving south from the strong/severe thunderstorms to our
north. If we can get the convective initiation going, storm
development will be rapid with a potential for storms to quickly
evolve into rotating storms due to the shear aloft. That convection
would be isolated to scattered through at least midnight with
isolated flooding possible until then.

Then eyes turn toward late tonight through early to mid afternoon
Tuesday. As the upper low continues to sag to the south tonight our
area comes into favorable dynamics with plenty of moisture available.
All convective allowing models and most larger scale models are
pointing to more widespread heavier rains developing after midnight
tonight across large parts of southeast Arizona, basically the area
covered by our Flash Flood Watch. What it is looking like is
repetitive bands of moderate to heavy showers with embedded
thunderstorms through this period of time. Confidence is increasing
for this to occur for areas east of Sells including the Tucson metro
area. There is potential for flash flood warnings to be issued before
dawn with impacts during the morning commute and continuing through
the remainder of the morning if this potentially significant scenario
develops as it looks like it could. An upper low pressure center this
deep, at this time of year, with access to tropical moisture is a
rare event and will need to be watched carefully as things can
develop quickly as was witnessed early this morning east of Phoenix.

The showers and thunderstorms will diminish Tuesday evening with a
relatively quiet/dry period Tuesday night into Wednesday morning. By
Wednesday morning the upper low should have settled down over
northern Baja (pretty amazing for September) with southerly flow
across southern Arizona and a deep tap into tropical moisture, and
our area should be in the favored NE quadrant of the upper low.
Wednesday afternoon well into Wednesday night a north-south oriented
rain band should develop in this scenario which will set up over a
location and linger, which is a set up for a relatively narrow band
(less than 100 miles) of heavy rain over an 8-12 hour period. The
problem is where will that sets up as under the band flooding is a
threat while outside of that band just scattered showers or storms.
Models have varied that band from the central portion of the forecast
area (eastern Pima/Santa Cruz) to the western portion
(western/central Pima county). It all depends on the final position
of the upper low so stay tuned to forecast updates over the next day
or two. At this time the best bet is for the central part of the
forecast area west to central Pima county.

The upper low will be slow to leave Thursday into Friday but at that
point the convection should be more scattered and less of a threat.
It will remain cool through this entire week into the early part of
the weekend. For the weekend we should be dry, however we will remain
in a "troughy" pattern keeping us a bit on the cooler side.

&&

.AVIATION...Valid through 25/00Z.
Isolated to scattered TSRA/SHRA becoming more widespread through the
evening/overnight hours and continuing thru Tuesday. Some storms
could be strong to severe with hail and strong wind gusts. Ceilings
will generally be SCT-BKN 4k-8k ft MSL with MVFR and even occasional
IFR ceilings in and around thunderstorms. SFC wind generally less
than 12 kts, favoring a SWLY/WLY direction thru 24/03Z and variable
in direction at other times. Wind gusts to 40+ kts near TSRA and with
any thunderstorm outflow boundaries. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered showers and thunderstorms
becoming widespread tonight into Tuesday ahead of a low pressure
system. Locally heavy rainfall and strong thunderstorm outflows will
be possible. Scattered showers and thunderstorms will then continue
Wednesday into Thursday as the upper low moves east. Dry conditions
are then expected Friday through the coming weekend. 20-foot winds
will be terrain driven and less than 15 mph, except in the vicinity
of thunderstorms where strong, gusty and erratic winds will be
possible.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 6 PM MST this evening through Tuesday
evening for Azz501-504-507>509-511>515.

Flash Flood Watch through Tuesday evening for Azz501-505-506.

&&

PUBLIC...Cerniglia
AVIATION....Zell
FIRE WEATHER...Zell

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TUCSON AZ
1127 PM MST MON SEP 23 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0925 PM     TSTM WND DMG     1 NNW WILLCOX           32.26N 109.84W
09/23/2019                   COCHISE            AZ   LAW ENFORCEMENT

            *** 2 INJ ***
            CORRECTS PREVIOUS TSTM WND DMG REPORT FROM 1
            NNW WILLCOX. POSSIBLE TORNADO WITH 3
            RESIDENCES (MOBILE HOMES) FLIPPED ON N.
            HAMILTON ROAD JUST NW OF WILLCOX. ADDITIONAL
            TREES AND POWER LINES DOWN ALONG FORT GRANT
            AND TAYLOR RD.

&&

JRM

Special Weather Statement
National Weather Service Tucson AZ
1206 AM MST Tue Sep 24 2019

AZZ504-507-513-240745-
Upper San Pedro River Valley including Sierra
Vista/Benson-Dragoon/Mule/Huachuca and Santa Rita Mountains including
Bisbee/Canelo Hills/Madera Canyon-Tucson Metro Area including
Tucson/Green Valley/Marana/Vail-
1206 AM MST Tue Sep 24 2019

...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL PIMA...WESTERN
COCHISE AND NORTHEASTERN SANTA CRUZ COUNTIES UNTIL 1245 AM MST...

At 1206 AM MST, Doppler radar was tracking a strong thunderstorm 8
miles south of Corona De Tucson, or 15 miles southeast of Sahuarita,
moving northeast at 25 mph.

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

Locations impacted include...
Vail, East Sahuarita and Corona De Tucson.

LAT...LON 3172 11072 3188 11095 3206 11063 3192 11045
TIME...MOT...LOC 0706Z 228DEG 20KT 3183 11073

AH

Special Weather Statement
National Weather Service Tucson AZ
127 AM MST Tue Sep 24 2019

AZZ501-502-240915-
Tohono O'odham Nation including Sells-Western Pima County Including
Ajo/Organ Pipe Cactus National Monument-
127 AM MST Tue Sep 24 2019

...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL PIMA COUNTY UNTIL
215 AM MST...

At 126 AM MST, Doppler radar was tracking a strong thunderstorm near
Organ Pipe Cactus National Monument, or 33 miles south of Ajo, moving
northeast at 25 mph.

Dime size hail and wind gusts up to 50 mph will be possible with this
storm.

Locations impacted include...
Gu Vo, Organ Pipe Cactus National Monument, Why, Gunsight, Lukeville
and Kuakatch.

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.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3227 11274 3213 11247 3185 11271 3196 11307
TIME...MOT...LOC 0826Z 212DEG 22KT 3190 11289

JRM

Special Weather Statement
National Weather Service Tucson AZ
220 AM MST Tue Sep 24 2019

AZZ502>504-515-241015-
Tohono O'odham Nation including Sells-Upper Santa Cruz River and
Altar Valleys including Nogales-Baboquivari Mountains including Kitt
Peak-Tucson Metro Area including Tucson/Green Valley/Marana/Vail-
220 AM MST Tue Sep 24 2019

...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL PIMA COUNTY UNTIL
315 AM MST...

At 219 AM MST, Doppler radar was tracking numerous strong
thunderstorms over the Tohono O'odham Nation with the strongest
storm over Topawa, or 8 miles south of Sells, moving northeast at 20
mph.

Half inch hail and wind gusts up to 50 mph will be possible with
these storms.

Locations impacted include...
Sells, Topawa, San Miguel, San Isidro, Kitt Peak, Ali Chukson, Gu
Oidak, Vamori, Cowlic, Fresnal, Choulic, Newfield, Coldfields,
No:ligk, Fresnal Canyon, Artesia, Hashan Chuchg, Kots Kug, Kupk and
Papago Farms.

LAT...LON 3175 11238 3209 11216 3194 11131 3150 11160
TIME...MOT...LOC 0919Z 248DEG 18KT 3180 11187

GL

Special Weather Statement
National Weather Service Tucson AZ
320 AM MST Tue Sep 24 2019

AZZ502>504-515-241115-
Tohono O'odham Nation including Sells-Upper Santa Cruz River and
Altar Valleys including Nogales-Baboquivari Mountains including Kitt
Peak-Tucson Metro Area including Tucson/Green Valley/Marana/Vail-
320 AM MST Tue Sep 24 2019

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL PIMA COUNTY UNTIL 415 AM
MST...

At 319 AM MST, Doppler radar was tracking a strong thunderstorm 7
miles east of Topawa, or 13 miles southeast of Sells, moving
northeast at 20 mph. Additional strong thunderstorms were located
near the International border southwest of Sells.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Sells, Topawa, San Miguel, San Isidro, Kitt Peak, Ali Chukson, Gu
Oidak, Vamori, Cowlic, Fresnal, San Pedro, Choulic, Newfield,
Coldfields, No:ligk, Cababi, Comobabi, South Comobabi, Santa Rosa
Ranch and Fresnal Canyon.

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.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3161 11195 3170 11223 3206 11214 3216 11140
      3151 11158
TIME...MOT...LOC 1019Z 237DEG 16KT 3179 11170

GL

Special Weather Statement
National Weather Service Tucson AZ
321 AM MST Tue Sep 24 2019

AZZ503-504-507-513-241100-
Upper San Pedro River Valley including Sierra
Vista/Benson-Dragoon/Mule/Huachuca and Santa Rita Mountains including
Bisbee/Canelo Hills/Madera Canyon-Upper Santa Cruz River and Altar
Valleys including Nogales-Tucson Metro Area including Tucson/Green
Valley/Marana/Vail-
321 AM MST Tue Sep 24 2019

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN PIMA...SOUTHWESTERN
COCHISE AND SANTA CRUZ COUNTIES UNTIL 400 AM MST...

At 320 AM MST, Doppler radar was tracking a strong thunderstorm near
Patagonia, or 14 miles northeast of Nogales, moving northeast at 40
mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
Nogales, Rio Rico, Whetstone, Patagonia, Sonoita, Elgin, Patagonia
Lake State Park, Nogales International Airport, Fort Huachuca, Kino
Springs, Canelo, Lochiel and Madera Canyon.

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.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3177 11086 3174 11036 3133 11052 3133 11106
TIME...MOT...LOC 1020Z 209DEG 33KT 3150 11074

Cerniglia