Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
211 PM MST Sat Sep 18 2021

.SYNOPSIS...
Increased moisture this weekend will bring a threat of showers and
thunderstorms to parts of the area. A weather system passing to the
north will result in breezy winds Sunday and Monday and a return to
dry conditions.

&&

.DISCUSSION...Today through Friday.

This weekend's weather will be driven by a shortwave trough lifting
northeastward across the Desert Southwest today ahead of a longwave
trough pushing across the PacNW and Great Basin tonight through
early Monday. Ahead of the shortwave, showers and storms will
develop from Ajo eastward to central Graham and Cochise counties
through this evening. Better upper-level dynamics remain to the
north of our area but with instability and moisture in place (PWAT
values: 1"- 1.8"), we expect scattered coverage of storms with a
few strong storms possible. Strong winds and lightning remain
concerns today with numerous outdoor events around the area this
weekend. Southerly steering flow of 10-20 mph should keep storms
moving along but a quick 0.5"-1" of rainfall could pose some
nuisance flooding issues. Storm chances for the Tucson valley
remain between 30-40 percent with timing between 3PM-7PM today.
Overall coverage and intensity of convection will gradually
decrease after sunset with isolated lingering showers or storms
possible to the east of Tucson overnight.

On Sunday, the shortwave will be on its way out as the large scale
trough pushes across the Western U.S. Showers and storm chances
shift eastward with drier air beginning to filter in from west to
east. Graham, Greenlee, and Cochise counties will see best chances
Sunday afternoon but isolated activity will still be possible across
eastern Pima (including Tucson) and Santa Cruz counties with a focus
over the higher elevations. Continued drying of the atmosphere
will limit any precipitation for Monday and Tuesday as ridge
builds in behind the exiting system. An uptick in winds is
expected for Sunday and Monday with the trough passage. Widespread
10-15 mph winds with gusts to around 20 mph are forecast.

Ensemble model runs begin to diverge Wednesday onward in the
handling of another potential shot of precipitation across
southeast Arizona later next week. In general, a trough will push
into southern Canada/PacNW mid-week as a piece of energy breaks
away from the main flow and drifts off the California coast late
in the week with little agreement as to where the high
reconsolidates. EPS remains drier in comparison with the GEFS but
both are advertising at least a portion of the area seeing some
chance for precip. As a result, there is low confidence in the
forecast Wednesday onward. Monsoon is quickly coming to a close
at the end of this month so we only have a couple more weeks to
tack on some more precip to our seasonal total.

&&

.AVIATION...Valid through 20/00Z.
SCT -SHRA/-TSRA will continue through 19/04z with SCT-BKN clouds at
10k-13k ft MSL. ISOLD -SHRA/-TSRA psbl again Sunday aftn mainly E of
KTUS/KOLS. wind gusts greater than 35 kts psbl vcnty SHRA/TSRA,
otherwise SFC winds less than 12 kts. Aviation not updated for TAF
amendments.

&&

.FIRE WEATHER...
Chances for showers and storms remain across much of the area this
afternoon and evening. On Sunday, isolated storm chances shift
primarily Tucson eastward, focusing over the higher elevations.
Dry weather is expected for Monday and Tuesday. Surface winds will
increase to 10-15 mph Sunday and Monday afternoons with gusts
around 20 mph possible out of the southwest. Stronger winds are
possible in the vicinity of any thunderstorms. Drier air will move
in early next week dropping afternoon RH values to 15-25 percent
by Tuesday. Temperatures remain within a couple degrees of normal.

&&

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

Public...Guillet
Aviation...Drozd
Fire Weather....Guillet

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Special Weather Statement
National Weather Service Tucson AZ
222 PM MST Sat Sep 18 2021

AZZ503-504-507-513-182200-
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-
222 PM MST Sat Sep 18 2021

...A strong thunderstorm will impact portions of east central Pima,
west central Cochise and northeastern Santa Cruz Counties through 300
PM MST...

At 222 PM MST, Doppler radar was tracking a strong thunderstorm near
Sonoita, or 22 miles southwest of Benson, moving north at 15 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Sonoita and Elgin.

This includes the following highways...
 Route 82 between mile markers 30 and 42.
 Route 83 between mile markers 28 and 42, and between mile markers 46
and 54.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3166 11051 3166 11069 3195 11072 3193 11042
TIME...MOT...LOC 2122Z 183DEG 12KT 3174 11059

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

AH