Sunrise Showers - Again

Thunderstorms yesterday stayed mostly on and near the mountains and rain amounts were not as heavy as during past two days. 54 of the 92 ALERT sites measured rainfall during the 24-hours ending at 5:00 am MST (~60% coverage). Only 5 sites had rain of half an inch or more, with one of those reporting just over an inch. Here at house we sprinkles late in day - Trace.

The MCS activity over northern Mexico weakened along the border with strongest thunderstorm activity making only limited progress on this side of the border. The CG flashes plot (above, from Vaisala and Atmo through 11 :00 pm MST last night) illustrates this, with yet another donut hole area over the metro region.

The 00 UTC sounding plot for TWC (below, from SPC) indicates a nice potential for evening and nighttime storms, given some organized forcing for upward motion. This did not happen, and there have been mostly debris cloud showers moving northwestward across southeastern Arizona. The troposphere below 400 mb had very light and variable winds, which was a serious problem.

There is an area of light showers moving across the metro area at sunrise - making today yet another challenge for forecasting. Seems like we've had this situation fairly often so far this summer. Have not found a morning sounding from TWC, but that probably doesn't matter, since it would have been contaminated by the local shower activity. Heavy cloud cover will reduce heating during the day and the high levels of PW (GPS indicates about 1.80 inches overhead this morning) may not lead to much storm activity, unless clear skies develop by early afternoon over some areas - most likely over Cochise County. At bottom is visible image from 6:10 am, showing the widespread cloudiness. Various high resolution forecast models have differing answers for this afternoon, but 06 UTC WRF-NAM and latest NWS HRRR forecast little activity for eastern Pima County this afternoon.

The morning sounding plot for TWC has just appeared and is below. Of note is the elevated CAPE indicated around 700 mb, which is apparently supporting the sunrise activity. Winds, while remaining mostly light, have become easterly from about 700 to 400 mb - the 15 to 20 kt winds near 700 mb may be response to the showers - basically the sounding fits with the bulk of discussion above.