Monday, June 29, 2009

Important Changes Noted This Morning

The 500 mb anticyclone still has three lobes this morning: one over southern Utah, one over far west Texas, and one over Texas/Louisiana border. The two eastern lobes are quite weak and the western lobe is predicted to dominate and to continue building toward the Four Corners. Middle-level temperatures are quite cool within the main anticyclone (-7 to -10C) and will help increase CAPE over much of the Southwest.

An inverted trough lies across New Mexico from the boot heel to the northeast corner and will probably brush across extreme southern Arizona and the borderlands this afternoon and evening. The vertical shear profile, both in this morning’s TWC sounding and in the NAM forecasts, is quite favorable for storms to propagate from the mountains into lower elevations.

The amount of low-level moisture has continued to slowly increase and the TWC sounding has 1.6 inches of precipitable water this morning. The southeast winds at low-levels may act to increase this some during the day. This morning’s sounding indicates that there will be decent CAPE this afternoon at low elevations with parcels at top of the boundary layer having theta-w values of about 23C or perhaps a bit higher.

All of this seems to come together for an active storm day in south central Arizona, after several days with the storms limited to the far southeast. My guess for this afternoon and evening is that it’s a 50/50 toss up for storms and rain here at the house. Given the shear profile there’s also a good likelihood that some storms may reach severe levels. So, it appears that a more interesting day is on tap.

Other things of note this morning – storms decayed over the GoC as they moved southeast from Sonora (see WV image on blog); large upper cyclone or inverted trough moving across north-central Mexico; another push of low-level moisture noted at Yuma as Td increased 10F from midnight to 1 am and there are widespread clouds across the lower Colorado Basin this morning; the past 24 hours saw no measurable rain over the Pima County ALERT gauge network.

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