That's a downburst; normal monsoon weather. One smashed up Sky Harbor
airport in Phoenix, and took the asphalt tiles off roofs in our neighborhood
a few weeks ago; they're still cleaning up. It's a lump of cold dense air
that may have been rain at some point, thousands of meters up there in the
clouds, but "evaporated" on the way down and fell on you! (Ours was full of
dust, too!)
----- Original Message -----
From: "Bill N" <freeholder@STARBAND.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, August 12, 2002 12:44 PM
Subject: Trip got interesting

We were camping on Mt. Graham in SE Arizona this weekend when a very unusual
event occured.  There were 9 of us sitting around the campfire around 4 in
the afternoon on Saturday.  It was partly cloudy and calm.  Within a 30
second period it went from calm to winds I would estimate at 70+ MPH, and
there was no warning.  We ran for our '81 Westy, and others ran for their
vehicles.  We heard trees cracking all around us.

Five minutes later, it was back to partly cloudy and calm.  There was no
rain associated with this, and the whole thing lasted a very short time.  We
hiked around taking stock and found that seven large ponderosa pines (2' or
larger trunk) had blown down within 100' or our campfire, taking several
smaller trees with them.

Although the poptop was up, and the sliding door was open the whole time,
the van had no problems.  The wind direction was from the rear, which I'm
sure helped.

Any weather experts out there have any idea what causes this sort of thing?
I am told by neighbors that a similar wall of wind blew through my home area
(about 40 miles away) that same afternoon.

Bill in the Southwest