Sunday, July 17, 2016
Chaotic Setting This Morning
Thunderstorm activity yesterday stayed off to our east to south to west - see 12-h plot of detected CGs above for 12-hours ending at 5:00 am this morning (from Atmo and Vaisala). Two sites in the far southern edge of the ALERT network recorded 0.04" of rainfall. The strong outflow forecast by yesterday's 06 UTC WRF-NAM did not materialize, and all-in-all it was another dismal day locally.
The situation this morning is chaotic as per the skies above when the sun rose behind Thimble Rock. Visible image below is from 6:45 am MST and shows the widespread cloudiness that is impacting much of southern Arizona. There appear to be at least a couple of residual MCVs nearby, but they are hard to locate precisely. There may be one just off to our west or southwest, while radar loops indicate another in Sonora south-southeast of Sierra Vista. Second below is an IR image from 6:00 am that shows an MCS over Sonora. This system is weakening; however, it may add more debris cloudiness to our local conditions later this morning - very messy situation.
The 06 UTC runs from the WRF both had problems. The NAM version forecast widespread early morning thunderstorms for eastern Pima County. The GFS version was not as bad, but appears to have also overdone the morning convection. So I have not looked at their forecasts in detail - we'll see what the 12 UTC versions forecast.
The morning sounding plot for TWC is shown below. The PW continues a bit over 1.25 inches with a deep, saturated layer in middle-levels. There is a mesoscale onion profile (probably from the MCV) from 600 down to 800 mb, with slightly cooled air below. Not much in the way of CAPE with this convectively-modified sounding. The wind profile is slightly better than yesterday, but in sum it is a pretty miserable sounding, and not one that leads me to anticipate much locally.
Currently the NWS forecast POPs (probability of measurable rainfall) for the airport are 20% today, 30% tomorrow, and 40% on Tuesday. Not sure what they are looking at for Tuesday. The 500 mb high shifts eastward but the models are not picking up any features moving around it that would help to increase moisture and/or storm activity - at least none that are obvious to me, but there may be something lurking in northeast Mexico that will be over our way by Tuesday. This time of year it is usually tough to figure out today and tomorrow - days 3 through 7 are often basically science fiction or fantasy.
Posted by Bob Maddox at 7:48 AM