The 02Z IR image above shows that MCSs in Mexico yesterday evening developed far south of the border. There were some storms later in southwestern New Mexico, where there is a bit more precipitable water. Conditions were very suppressed in Arizona yesterday with record level heat.
This morning (28 August 2009) the 500 mb anticyclone is centered over Laughlin NV with very warm temperatures west and north of the center. Cooler, but very dry air continues advecting around the east and south quadrants of the high. It appears that this anticyclone is now acting as a lobe of the Pacific subtropical high, thus the very dry fetch. The high is forecast to sink a bit south and elongate west-to-east during the next 36 hours, keeping Arizona mostly under upper-level subsidence - more dry heat.
There is a distinct disturbance at the southern end of the Gulf of California, but in the short-term this feature moves off to the west and is replaced by what will perhaps be a stronger invert trough. There is also an upper-level trough moving southwestward across southern New Mexico and this feature will have little impact, except perhaps to enhance MCS development in Mexico tonight.
In the longer-term, the next couple of inverted troughs are forecast to move more to the north and west and, inconcert with troughing in the Pacific and much lower pressures in the Great Basin, will likely bring a surge of low-level GoC moisture back into Arizona by Sunday am. The deeper subtropical moisture may also shift north Sunday afternoon and Monday as the 500 mb anticyclone is pushed to the east. There may be a Tropical Storm thrown into the mix by Sunday. So, there's still hope that we will see some more storms as August closes out.
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