Tuesday, July 07, 2009

Amazing Changes Overnight

Miscellaneous Ramblings

Sky at sunrise looked quite chaotic, much like it does on big storm days. Was a muggy 80F at 6am here at house. ACC all directions except northwest and even some low cloud based below the tops of the Catalinas and the Rincons. Amazing changes as the dry Pacific air aloft battles the influx of low-level moisture from the Gulf of California and from outflows from borderland storms.

Significant Gulf of California surge began yesterday morning between 7 and 8 am and has continued ever since. It’s remained fairly deep extending up to 4 to 5 thousand feet as per the radar VADs. Tucson’s morning sounding is quite impressive below 525 mb and indicates precipitable water of 42.57 mm – as said above a remarkable change overnight. The GPS data indicate that the sounding is a bit too wet – about 3 to 5 mm.

The WRF sounding Mike Leuthold sent out yesterday was very moist – BL mixing ratio of 12 g/kg and lifted parcel theta-w of 24C – both values are higher than has been observed yet this summer. The WRF certainly picked up on the changes, but still predicted only isolated convection mostly south and east.

Temperatures above 525 mb are very warm and will be increasing a bit during the day. Phoenix sounding much drier than down here and that superheated air will again be trying to advect this way. The 500 mb anticyclone begins its eastward position shifting during the day and much of southern Arizona should be under the influence of subsidence in the upper troposphere.
So the question is how this battle will play out during the day – will the nearby mountains trigger significant storms before the hot air aloft chokes everything down? Will the low desert BL air with no CAPE invade the local area? Tough questions – my guess would be that things get too hostile in the Tucson metro region and that storms will again be mostly east and south. I still would bet Mike Leuthold a beer that the WRF predicted afternoon sounding for Tucson will prove too moist and unstable when the afternoon sounding data come in. But would I bet a crisp Ben Franklin – no way!

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