Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion...UPDATED
National Weather Service Tucson AZ
1007 AM MST Sun Sep 5 2021

.SYNOPSIS...Expect an increase in thunderstorm coverage today and
Monday compared to the past couple of days, with temperatures a
couple degrees below normal. After Labor Day, storms are mainly
confined to the International border and central/western Pima County.

&&

.DISCUSSION...Upper air plots this morning place high pressure over
the southern Great Basin with easterly/northeasterly flow over
southeast Arizona. Scattered to locally broken skies were indicated
by satellite imagery, mainly from Tucson eastward, with a few
showers already developing over the higher terrain of Cochise
County. A shortwave will round the ridge into this afternoon,
bringing upper level support for showers and thunderstorms into an
already primed environment. The 12Z KTWC RAOB measured 1.6" of PWAT
with plenty of CAPE but a stout cap, but the combination of daytime
heating and the shortwave should be able to erode that CIN with
little issue. Look for the potential for heavy rainers, and with
DCAPE of almost 1400 J/kg, strong to severe winds will also be a
threat. HREF members are in good agreement regarding storms
developing across the higher terrain and sustaining into the
valleys, generally moving from NE to SW. In this rim shot scenario,
strong gusts in the Safford area are almost a sure bet, and we
increase the potential for some blowing dusts across Pinal and
northeast Pima Counties. Tucson is also in the conversation for some
potentially strong to severe storms, particularly between 22Z and
02Z this evening. After that, CAM solutions trend downward pretty
quickly with the loss of daytime heating, with most of our
convection ending by 03Z to 05Z tonight.

High pressure continues to push east to northeast on Labor Day for
less convective coverage in our area. High temperatures within a few
degrees of normal through about midweek. No near-term updates needed
this morning. Additional details available with the afternoon
package. Please see the remaining sections until then.

&&

.AVIATION...Valid through 06/18Z.
ISOLD-SCT TSRA/SHRA this afternoon and evening with SCT-BKN clouds
10k-15kft MSL, generally clearing overnight into Monday morning.
MVFR CIGS/VSBYS may accompany a few of the stronger storms, along
with BLDU and wind gusts in excess of 40 kts. SFC wind outside
convection generally less than 12 kts. Aviation not updated for TAF
amendments.

&&

.FIRE WEATHER...Expect scattered showers and thunderstorms this
afternoon and evening. By Monday, storms should concentrate over our
western zones and along the International border through the middle
of the week. 20-foot winds will generally be less than 15 mph when
not influenced by thunderstorm gusts. Minimum RH values will remain
well above critical thresholds this week.

&&

PREV DISCUSSION...Satellite shows mostly cloudy skies across the
majority of the CWA. This will likely keep low temperatures elevated
again this morning. Hi-res guidance is hinting that today will
likely have greater storm coverage than yesterday. Expect scattered
showers and thunderstorms from central Pima County eastward during
the afternoon and evening. Storms will first form over the higher
terrain then propagate west/southwest into the lower elevations
where there should be sufficient CAPE to keep them alive. A weak
upper level disturbance will also be moving through lending some
dynamical support to storms. The HRRR and U of A models show fairly
strong outflows from storms in Pima and Pinal Counties, which could
create some blowing dust issues in the evening. Strong wind gusts
from downdrafts will be possible with DCAPE values around 1000 J/kg.
Brief and localized heavy rainfall will also be a threat.

Monday the area of high pressure remains over Nevada with SE Arizona
under east/northeast flow aloft. The best moisture/instability looks
to be along the international border and western Pima County. Expect
isolated to scattered storm activity in this area along with the
White Mountains. Under the influence of the northeast flow storms
will try and move off the White Mountains into the lower elevations,
but the environment does not look favorable and storms will likely
not survive long off the higher terrain.

During the middle of the week the ridge will slowly drift east as a
trough moves towards the west coast. As this happens moisture will
mainly be confined to the western part of the CWA and along the
international border. Tuesday into Thursday expect isolated to
scattered showers and thunderstorms mainly along the international
border and central/western Pima County. Tuesday there could be a
some isolated storms in the White Mountains. Tucson will be on the
northern periphery of the storm activity.

By Friday most of Cochise, Graham, and Greenlee Counties look to be
dry with isolated storms possible from Tucson westward. Next weekend
there is still considerable uncertainty with how far south the
trough will move, which will determine if we will lose more of our
monsoonal moisture.

&&

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

&&

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Special Weather Statement
National Weather Service Tucson AZ
1152 AM MST Sun Sep 5 2021

AZZ503-513-051915-
Dragoon/Mule/Huachuca and Santa Rita Mountains including
Bisbee/Canelo Hills/Madera Canyon-Upper Santa Cruz River and Altar
Valleys including Nogales-
1152 AM MST Sun Sep 5 2021

...A strong thunderstorm will impact portions of southwestern Cochise
and southeastern Santa Cruz Counties through 1215 PM MST...

At 1152 AM MST, Doppler radar was tracking a strong thunderstorm near
Parker Canyon Lake, or 18 miles southwest of Sierra Vista, moving
west at 10 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Parker Canyon Lake and Lochiel.

This includes Route 83 between mile markers 3 and 10.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3149 11076 3151 11041 3133 11036 3133 11073
TIME...MOT...LOC 1852Z 081DEG 8KT 3139 11051

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

RH