Monday, July 14, 2014

July 12th VS July 13th

The mess that I found confusing yesterday morning sorted itself out by late afternoon and much of Arizona experienced a widespread storm event. My long-term experience has been that downslope situations, as per yesterday morning to mid-day, usually lead to big storms west and northwest of Tucson, with Phoenix often experiencing severe thunderstorms in these settings. Once-in-awhile, however, things come together late in the afternoon in the Tucson area (perhaps about 1 in 6 times? - which is just a guess) and produce severe thunderstorms locally. This is what happened yesterday, with one of those unusual events that also had the storm focus at low elevations rather than high. Rainfall coverage was essentially 100% across the low elevations of the Tucson metro area and considerably less up in the mountains. So, a very unusual day and I'm going to compare a few charts and graphics. First - the Tucson 00 UTC soundings, as per:

Sounding above is that from 5 pm MST on 12 July, while that below is from 5 pm on the 13th. Winds were east-southeasterly yesterday but northeasterly the day before.  PW was very similar both days but the BL was hotter yesterday and CAPE, while not at all impressive, was greater yesterday afternoon. Probably of most importance was that by release time yesterday the downslope winds had become very light. Convective cloud bases very very high both days at around 650 mb - certainly not a pure mT airmass. The differences between the soundings are fairly subtle, which is the signature aspect of summer weather out here - subtle differences in the setting can lead to big differences in the convective regime.

The CG flash plots ending at 12 UTC on Sunday morning (above) and this morning (below, Monday, July 14th) demonstrate the big increase in storm activity yesterday - which is why I wish that someone had a quantitative count product for CGs. Note the high CG flash density over the metro Tucson area yesterday.

Finally, I show some comparisons between the west and east metro sectors of the ALERT network. Above is the west sector. Top above shows 4 day rainfall totals from noon on the 9th through noon on the 13th, yesterday. Directly above is same, but for past 24-hours ending at 7 am MST this morning - wow! Bottom two are same plots for the east metro sector. 

So, quite some event yesterday, especially in the context of the past 5 days.

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