Saturday, July 28, 2012
Strong Outflows But Light Rains
Yesterday played out about as expected. Afternoon and evening storms made it west to the Rincons and then decayed. A large MCS in northeastern Sonora was the dominant feature during the night (04 UTC IR on 28th above). A strong outflow blew through the Tucson metro area from the decaying storms at around 8:30 pm MST. I estimated gusts here were 50+ mph. Light showers from the storm debris at house around midnight amounted to 0.04". Across the ALERT network about 45% of the stations recorded rain in past 24-hours. Amounts were generally ligh, with most rain up on the Rincons - no stations reported more than 0.39". So more wind than rain last night. The time series of T and Td from Atmo's roof (below) shows the dramatic first outflow and then indicates several additional small outflows during the night - each of these continued to increase Td.
The GPS vs RAOB PW time series (above) shows two distinct jumps during the night, kicking PW up to about 1.75" this morning. So, with outflows and recycling, the Tucson area is now very moist. The far southwest part of Arizona has experienced sharp Td increases as convection affected the middle GoC, but PW remains low out there. This morning's Tucson sounding (below) indicates moderate CAPE. Winds aloft are still not great, but models forecast stronger, somewhat uni-directional winds this afternoon. Weak inverted trough continues moving westward across Sonora and the Borderlands. The near-surface cooling was not great during the night and sunshine should break through in places and get storms going earlier today.
Finally, large amounts of debris cloud reach from northwestern Mexico northward and northeastward across much of Arizona and Colorado. Thickest cloud cover appears to be across south-central Arizona. Both the WRF-GFS and NAM forecast numerous storms during the morning hours today and seem once again out sync with the timing of events. Threat of local heavy rains and microbursts is significant today.
Posted by Bob Maddox at 8:02 AM