Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
844 AM MST Sun Aug 29 2021

.SYNOPSIS...Scattered afternoon showers and thunderstorms continue,
increasing in activity this week as tropical moisture moves into
the area. Concerns for heavy rainfall leading to flash flooding
will also rise as a result.

&&

.DISCUSSION...The 12Z KTWC sounding still around 1.3 inches
precipitable water, but showing less shear and lower convective
potential compared to yesterday. SREF plumes are forecasting the
lower shear and CAPE environment to continue into max heating this
afternoon. Not as organized as yesterday but a scattered
thunderstorm forecast still looks good with a hint of merging
outflows in Pinal county late in the day as per latest HRRR and UA
WRF-RRGFS. Current forecast has good trends.

Hurricane Nora continues to struggle a bit as it takes a track too
near the west coast of Mexico for it's own health. Still pushing
a long fetch of deep moisture northward toward Arizona for a
sustained increase in storm chances this week.

&&

.AVIATION...Valid through 30/12Z.
FEW-SCT clouds at 8k-12k ft MSL through the forecast period. ISOLD-
SCT SHRA/TSRA after 30/19Z. MVFR conditions and mountain-top
obscurations near TSRA, along with wind gusts up to 45 kts.
Otherwise, SFC wind favoring an ELY/SELY direction and generally
less than 12 kts. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Isolated to scattered showers and thunderstorms are
expected for much of the forecast area through Monday. Deeper
moisture will then overspread the area Tuesday through Thursday as
moisture associated with the remnants of Nora shifts northward. This
will result in increasing precipitation chances mid to late next
week across southeast Arizona, with potentially heavy rainfall at
times. 20-foot winds will generally be less than 15 mph when not
influenced by thunderstorms gusts.

&&

.PREV DISCUSSION... /issued 323 AM MST Sun Aug 29 2021/
Radar echoes have diminished across the forecast area early this
morning, with a few remnant light showers lingering in northern
Sonora. IR satellite imagery shows cloud tops gradually warming
and diminishing from east to west. PWs range 1.6" in western Pima
County to around 1" east toward the NM border. The overall pattern
is defined by a weak upper ridge to our north, producing east to
southeast steering flow. Thunderstorms are expected to develop
again this afternoon, although MLCAPEs aren't forecast to be as
unstable as yesterday. This should inhibit the overall severity of
storms, but models still develop isolated to scattered
precipitation into the evening hours. HREF neighborhood
probabilities focus on two favored areas of development--one being
over the higher terrain of Graham/Greenlee Counties and the other
south to southwest of Tucson along the International Border.

Monday's activity looks to nudge up as moisture continues to
increase out ahead of the tropical system Nora. Currently Nora is a
category 1 hurricane, drifting up the Mexican coastline near
Mazatlan. The NHC forecast track brings Nora up the coast,
eventually eroding as it turns north on Tue/Wed moving across
northern Sonora. Regardless of the exact path of Nora, models still
anticipate a surge of moisture and widespread rainfall chances
Tuesday through Thursday. WPC has issued a slight risk of excessive
rainfall beginning Tuesday as PWs increase west to south of Tucson.
This area matches up with the GEFS mean QPF forecast values being in
the 90-95th percentiles. Heavy rainfall potential becomes more
expansive on Wednesday, which based on the ECMWF EFI and GEFS
forecasts should be the most active period. The precise area of
coverage remains in question, whether the north/south axis of heavy
rain sits across western or central Arizona. Thursday could
transition from heavy rain toward a more severe weather scenario as
20 kts of mid-level southerly/southwesterly flow sets up across the
region.

&&

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

Howlett/Dang/Meyer

Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson

Special Weather Statement
National Weather Service Tucson AZ
232 PM MST Sun Aug 29 2021

AZZ507-508-513-292215-
Upper San Pedro River Valley including Sierra
Vista/Benson-Dragoon/Mule/Huachuca and Santa Rita Mountains including
Bisbee/Canelo Hills/Madera Canyon-Eastern Cochise County Below 5000
Feet including Douglas/Willcox-
232 PM MST Sun Aug 29 2021

...A strong thunderstorm will impact portions of central Cochise
County through 315 PM MST...

At 231 PM MST, Doppler radar was tracking a strong thunderstorm 15
miles southeast of Pearce-Sunsites, or 28 miles northeast of Bisbee,
moving northwest at 5 to 10 mph.

HAZARD...Wind gusts up to 50 mph and half inch 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...
Pearce-Sunsites and Sunizona.

This includes the following highways...
 Route 181 between mile markers 39 and 42.
 Route 191 between mile markers 25 and 48.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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 3176 10957 3162 10981 3184 11006 3200 10969
TIME...MOT...LOC 2131Z 146DEG 6KT 3178 10971

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH

Meyer