Tuesday, August 16, 2016

Thunderstorms Return To Southeast Arizona Today

Edited to add: Forgot to mention below - At 7:00 am MST this morning the observed dewpoint temperature in Yuma was 72F, but north up the river in Las Vegas dewpoint was 17F. A slight difference of only 55F.

Thunderstorm activity continued to be very suppressed over southeast Arizona yesterday - above shows detected CGs through 24-hours ending 5:00  am MST this morning (from Vaisala and Atmo). Northern Mexico was also suppressed to what seems an amazing extent. Below shows CGs for 12-hours ending at midnight last night emphasizing the near total lack of thunderstorm activity across all of northern Mexico.

The time-series of GPS PW at the university for past seven days (above) indicates steadily decreasing amounts from the 12th through the 14th, but with a slow and slight increasing trend now apparent. Values however continue around 30 mm, which is more representative of pre-monsoon conditions.

The morning sounding from TWC on campus (above skewT plot from SPC) shows several aspects of interest. The troposphere continues to be essentially a two-layer atmosphere above and below 500 mb. Temperatures at top of the lower layer have decreased considerably as moisture has slowly increased and the boundary layer has become very deep. However, there is a very nasty inversion centered at 500 mb, and this feature will be the important player today, as it limits available CAPE considerably and caps convection rooted at lower elevations. This inversion is, however, maximized around Tucson, when other soundings are considered across the region. So its evolution during the day will be important.

The 06 UTC run of the WRF-NAM at Atmo forecasts some storms in Pima County at 7:00 pm (above), and more so in Pinal County. The sounding forecast for TWC at 6:00 pm (below), however, has almost no inversion present and what there is has been lifted up to around 400 mb - quite a difference from the morning observation. There's no real way to know how the inversion might be changing today, other than to keep an eye on the character of any convection that occurs - development of Cbs to the north would indicate that the model was on track.Any storms that might develop would have the potential to produce strong, local downbursts due to the very deep boundary layer.

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