Blowing Dust Advisory 31, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
115 PM MST Thu Sep 7 2017

.SYNOPSIS...Scattered thunderstorms west of Tucson this afternoon,
with a few mountain storms elsewhere. Increasing moisture will bring
a good chance of storms Friday into Saturday. Thunderstorm chances
will decrease early in the new week as high pressure builds overhead
and we lose a little moisture.

&&

.DISCUSSION...We're still fighting dry air in eastern areas, but
starting to regain a southerly component to our flow as the regional
ridge shifts a little east of us. The 12Z KTWC sounding was showing
a little better storm support, with precipitable water up to .9
inches along with a little more convective potential. We still are
seeing better moisture and instability west of Tucson with a nice
moisture convergence field, dynamics associated with a weak remnant
circulation out of Sonora, and an upper level diffluent field
between the low near the west coast and the ridge. As mentioned this
morning, our main focus remains over the Tohono O'Odham nation,
western Pima and southwestern Pinal counties. Possible organized
outflow with dust concerns. With good agreement among University of
Arizona WRF model forecasts, we have issued a blowing dust advisory
for our previously discussed main areas of concern. Tucson might get
clipped as well, but most of the action should pass just west and
northwest of the city.

As the pattern phases a little further east, the favorable area for
enhanced thunderstorm development will shift east with it, including
more of our CWA Friday and Friday night into Saturday. Our main
concern with that scenario is debris and boundary layer cooling from
any activity we have later today and tonight. Best guess is that we
will recover enough for storms, but they may not have quite the
punch they might have had. Enough moisture for locally heavy rain as
well.

By later Sunday and Monday, the ridge is expected to build back
westward again in response to the low lifting northward from off the
southern California coast, and extensive modification of the pattern
downstream from tropical influences. That will inhibit thunderstorm
development once again as we do the typical September thing of more
frequent interruptions to the waning monsoon flow.

&&

.AVIATION...Valid thru 09/00Z.
Isolated to scattered -TSRA/-SHRA this afternoon and evening west of
KTUS, with isolated -TSRA near mountains east of KTUS. Coverage
increasing Friday. Surface wind ely to sly 5-15 kts with occasional
gusts near 20 kts, stronger winds near thunderstorm outflows.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...A chance of showers and thunderstorms this
afternoon, especially west of Tucson. Increasing storms Friday
into Saturday. A modest drying trend will see a lesser chance of
thunderstorms early in the new week. 20-foot winds will generally
be less than 15 mph into next week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Blowing Dust Advisory until 6 PM MST this evening for AZZ501-502-504-
505.

&&

Meyer

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