Saturday, June 2, 2012

The Inverted-V Sounding

After several days of blue skies, some weird white stuff spread over northern Utah last night.  The clouds can be seen in this morning's infrared satellite image.

Hoping for rain?  It's unlikely.  The problem is that it is bone dry in the low levels.  This morning's upper-air sounding from the Salt Lake City International Airport shows what meteorologists call an inverted-V in which the temperature (red line) and dewpoint (green line) traces form an upside down V.

Such a sounding indicates well-mixed, but dry conditions in the low levels.  In this case, the inverted-V is quite deep, which means any precipitation falling from the high-based clouds will need to fall through over 3000 meters of increasingly dry air before reaching the valley floor.  If a strong convective cell pops up today, perhaps it could generate measurable precipitation on the valley floor, but in all likelihood virga (snow and rain that evaporate before reaching the ground) will dominate.

Inverted-V soundings are also favorable for strong downdrafts and gusty winds that are generated as precipitation falling into the dry low levels evaporates and cools, creating locally dense, negatively buoyant air that quickly crashes to the ground.  The resulting winds, however, can be locally strong.

Finally, any thunderstorms that form under these conditions are potentially life threatening.  People have a habit of not seeking shelter during so-called "dry thunderstorms."  As the saying goes, when thunder roars, head indoors, even if it is not raining.  Now is a good time to review our past post on lightning safety.

1 comment:

  1. Am using this info and sounding for my aviation talk at the Spanish Fork Airport next week, thanks Jim!