May 17, 2009 - Monsoon-type pattern arrives early in SW U.S.

For a week now, I've been watching models and satellite pics show evidence of the North American Monsoon beginning to establish itself in central Mexico. Placement of highs, lows and upper jet patterns began depositing copius amounts of subtropical moisture in the central highlands of Mexico for the past 8 days ( a generally classic pre-monsoon setup). Models suggested that a classic Four-Corners high would anchor itself, along with a weak upper level low spinning northward off the Baja coast. Mosture in west Texas would be drawn westward across NM and into AZ, and eventually, SoCal.

Well, this has come to fruition and the next several days will likely see an increase in thunderstorm action in central AZ, peaking about Wed (May 20). SoCal will be on the western fringe of this moisture shield, and SPC has already included much of California in a general thunderstorm zone for tomorrow. Now, granted these will not be of the severe variety we have been seeing in the Plains, Mid-west, and South over the past 2 months, but because of the dry surface levels and enhanced dynamics provided by the spinning low moving in off the SoCal coast, microburst conditions could occur and the areas between Casa Grande and Phoenix may experience strong "haboob" dust storms as a result. Also, the wildfire danger will be elevated as the risk of dry lightning will be present in all areas, including SoCal.

What does this mean for the rest of the season? Well, it's anyone's guess, but the CPC thinks we are in for an earlier, stronger, wetter, and longer monsoon pattern. Let's see how this all plays out :-)