Heavy Clouds At Sunrise

Yesterday storms occurred to south and southeast and also briefly on the Catalina and Rincon Mountains. A large MCS developed (see 03Z IR image above) with most of the active cells staying south along the borderlands (Nogales had thunder, rain, and gusts to 46 mph), but outflows spread north through most of southeast Arizona bumping the dewpoints back up. Heavy clouds covered the sky this morning – remnants from last night’s MCS. Measurable rain occurred in the past 24-hours at 6 of the 93 Pima County ALERT gauges, with Manning Camp high in the Rincons measuring 0.67”.

The most interesting changes overnight occurred across south-central and southwestern Arizona where a surge of low-level moisture from the Gulf of California occurred, bringing some dramatic 24-hour increases at 6 am. As per:

Needles CA +33F; Yuma AZ +24F; Phoenix AZ +21F; Casa Grande +18F

So two issues for today will be: 1) how quickly will the cloud cover break up to allow heating? 2) will low-level moisture continue to slowly increase? Note that with precipitable water up to around 40mm in the PHX and TWC soundings we have had a nice increase, but the really moist subtropical air has not quite moved into Arizona. The soundings indicate that we will probably still have quite limited CAPE at low elevations this afternoon. South winds at Guaymas extend up to 700 mb, so there are good signs that things will continue to improve today and tomorrow.

The western circulation center of the massive, mid-level anticyclone that covers the southern half of US and much of the subtropics has consolidated along the New Mexico/Arizona border. This provides a nice wind profile for moving mountain storms toward the deserts. The NAM forecasts that the subtropical moisture will push north and interact with a weak N-S trough embedded within the anticyclone – the result is that the model forecasts the most active days to occur on Thursday and Friday. Since the model is often slow, tomorrow might be the day that we see much increased activity, after another uptick today.