Wednesday, June 24, 2009


A number of unusual things have been going on during the past 24 hours.

First – minicane Andres appears to have totally dissipated during the night. The higher, cold cloud moved rapidly away to the west during late night/early morning and there appears not even to be a remnant low in the visible imagery. So, it appears that Andres might have helped move deeper moisture a bit north up the Gulf of California. But, if lower-level moisture increases dramatically tomorrow over south-central Arizona it will be due to the following factors.

Second – a pronounced upper-level cyclone is moving westward across central Mexico and will be a player in our weather as it appears that it will pass by at the 36-48 time frame, as it pulls northward ahead of the cutoff low that moves onshore during this period.

Third – the NWS models bring the Pacific, middle-latitude cutoff across the Great Basin, allowing the massive, middle-level anticyclone over the Plains to back westward over Arizona and new Mexico. However, the ECMWF continues to keep the anticyclone further east, allowing a moist flow to continue over the Southwest for a week or so.

Fourth – compare the TWC and ELP soundings this morning. The moist plume around the anticyclone has ELP in a deep, moist and unstable airmass. The light winds and CAPE in that sounding indicate a clear threat for flash floods. In contrast, TWC has a considerably less moist sounding with a deep residual boundary layer that extends almost to 500 mb. Moisture has been increasing slowly but the sounding still does not have CAPE. The Phoenix sounding is similar and its old boundary layer extends to just above 500 mb – the difference in old boundary layer heights at TWC and PHX lead to a deceptive difference of 4C in 500 mb temperature!

It appears that the evolution of all of the above may lead to a significant increase in moisture tonight and tomorrow over at least southeastern Arizona. So, the chance of storms will increase substantially tomorrow afternoon and evening. After that, it appears to be a watch and wait scenario.

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