Emily's Moisture Arrives in Phoenix

Deborah writes:

a weird wind has begun--clouds are all over the s/e--wind picking up now.......

Yay! Emily moisture is arriving!

I'm a bit befuddled why the Phoenix dewpoint isn't rising, though. Instead, it seems to be dropping. It's like a patch of dry air is lingering along the surface of the Valley of the Sun. Maybe the dewpoint will start going up shortly, but if it doesn't rise by much, there's a risk of a dust storm later today, as maturing thunderstorms get going (downbursts get caused when the raindrops in a downdraft evaporate into drier air - like a swamp cooler, the drier the air into which the downbursts sink, the more effective the cooling, and the more powerful the downburst gets, in a runaway, violent process).

It's interesting looking at this morning's Chihuahua sounding: the air is holding so much moisture there, they couldn't get a downburst even if they tried. Tucson is drier, though, so, like Phoenix, they may get a dust storm too. Friday should be the day most at risk of downbursts, before the moisture fully infiltrates everywhere.

Right now, there is a set of thunderstorms along the Yucatan east coast, which will drift NW over time, and should give a real punch to AZ rainfall by the middle of next week.