Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
954 AM MST Mon Aug 24 2020

.SYNOPSIS...High pressure will build overhead and bring hotter
temperatures most of this week. Near record heat today and
Tuesday, and maybe late in the week as well. We'll keep enough
moisture for a chance of thunderstorms, but most days will be
below average for late August, with day to day variations in
coverage and intensity.

&&

.DISCUSSION...Another smokey start to the morning across
Arizona as fires continue burn across the southwest. Looking at
another hot day across the lower deserts, with many locations taking
a run at record heat. Hi-res guidance shows thunderstorm activity
across two favored areas. One is the typical higher terrain of the
White Mountians. The other is across central to western Pima County,
where dew points are in the 60s and the best CAPE values this
afternoon. DCAPEs are also quite significant under this intensive
heat regime and organized outflows are possible with the potential
for blowing dust. Thus, a Blowing Dust Advisory was issued with the
morning update to account for this hazard. Please see the discussion
below for more details on what's to come.

&&

.AVIATION...Valid through 25/18Z.
FEW-SCT clouds 10k-14k ft MSL this morning with a few hours of SKC
around midday today. ISOLD-SCT TSRA/SHRA this afternoon through this
evening, particularly west of KTUS and across the White Mountains NE
of KSAD. Some +TSRA will be possible with reductions in CIGS/VIS,
MTN obscurations and wind gusts over 40 kts. Otherwise, SFC winds
generally less than 10 kts this morning becoming WLY/SWLY 8-12 kts.
Winds decrease overnight into Tuesday morning. Aviation discussion
not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered showers and thunderstorms this
afternoon through this evening, with a focus across the White
Mountains and west of Tucson. Drier conditions and hotter
temperatures this week slightly reduces shower/thunderstorm
coverage. Today and Tuesday should be the hottest days while precip
coverage looks to be the most limited on Thursday and Friday.
Minimum humidities 10-20 percent across the valleys and 20-30
percent in the mountains today through Thursday with good overnight
recoveries. A little more moisture arrives Friday into the weekend.
20-foot winds generally remain less than 15 mph outside of any
thunderstorm gusts which could reach 40+ mph.

&&

.PREV DISCUSSION...Our weather continues to be dominated by strong
high pressure from the desert southwest through the front range of
the Rockies. Heights and thicknesses once again support record
afternoon highs to start the week, as per an Excessive Heat Warning
today and Tuesday.

We've seen a little drying push in from the east, but we maintain
enough moisture for thunderstorms with precipitable water values
ranging from about 1.15 east to 1.55 west. With the strong high, mid
levels will be a tad warm and tend to tamp down on valley
thunderstorm chances. Two main areas have the best chance of storms
over the next couple of days. The first is the Mogollon Rim with
initial buildups over the mountains, with both the orientation of
the mountains and flow around the high favoring outflows pushing
southwest and west. The second area will be areas southwest of
Tucson (from about Nogales to about Sells) where an area of upper
level diffluence at the inflection point of the upper level portion
of the high will combine with better convective potential values for
a good chance of storm development today and Tuesday. Best guess is
one of these two days Metro Tucson will get involved, either on the
fringe of the favorable area to the west and southwest, or from a
strong organized outflow from the rim.

We'll maintain enough moisture for a daily chance of thunderstorms
Wednesday into Friday, but coverage should be below average for late
August (nothing new there). As the high center sags slowly southward
we'll gain a southerly component to our flow. This will help, and we
ought to manage a thunderstorm upswing over the weekend, but
initially it could push temperatures back up to excessive heat
levels toward the end of the week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 10 AM this morning to 8 PM MST
Tuesday for AZZ501-502-504>506-509.

Blowing Dust Advisory from 2 PM this afternoon to 9 PM MST this
evening for AZZ501-502-505.

&&

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Special Weather Statement
National Weather Service Tucson AZ
Issued by National Weather Service Phoenix AZ
121 PM MST Mon Aug 24 2020

AZZ501-502-242100-
Western Pima County Including Ajo/Organ Pipe Cactus National
Monument-Tohono O'odham Nation including Sells-
121 PM MST Mon Aug 24 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN PIMA COUNTY UNTIL
200 PM MST...

At 121 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from 7 miles east of Ajo to 6 miles north of Organ
Pipe Cactus National Monument. Movement was west at 10 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Ajo, Organ Pipe Cactus National Monument, Why, Gunsight and Kuakatch.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy rainfall is also occurring with these storms, and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

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

&&

LAT...LON 3250 11299 3251 11277 3247 11261 3193 11267
      3193 11299 3196 11308
TIME...MOT...LOC 2021Z 096DEG 8KT 3238 11274 3205 11277

Feldkircher