Unusual Event During The Night

Late in the afternoon yesterday thunderstorms had developed off in the highlands southwest of Tucson (see 5:30 pm MST visible satellite image above). The anvil cloud from these storms spread overhead, as well as a line of building TCU, at dusk. David Monthan AFB had thunder and rain before midnight; however, the surface winds remained strong from the east. The same occurred at the airport in the early morning hours. The lack of wind shifts seems to indicate that these very slow moving storms were rooted in unstable air aloft above the easterly flow associated with the strong backdoor front that had moved through the metro area sometime Tuesday afternoon. Indeed, this morning's sounding seems to show that the storms are being fed from the 800 to 700 mb layer - the more usual scenario for nighttime storms would be that they were associated with various outflow boundaries sloshing around the region. Note that the models were all consistent in forecasting this strong frontal passage 4 to 6 days in advance, and even indicating that it would push westward to the California deserts with moisture and storms (which it did!).

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Rainfall reports this morning - 0.07" here at house; TUS 0.29"; DM 0,23"; and Nogales 0.01". In the ALERT network 31 of 93 gauges had rainfall during the night with the highest amount being 0.55" at a aguage near Green Valley; and two RAWS gauges to the south of Tucson had rainfall.

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The middle IR image, from this morning, shows TS Frank, a morning MCS at the mouth of the GoC, and deeper cloud pushed up to the middle GoC. The models have been very consistent this week in indicating that the tropical disturbance off Baja would be associated with a nothward push of deep moisture and this appears to be well underway.

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There was a nice morning rainbow (at least half of one) visible from the house this morning at a bit before 7 am MST. I took the bottom photo looking west at the rainbow from the backyard here.

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Final comment: I've been very puzzled as to why there was almost no mention in the Tucson NWS FDs of the strong cold front coming down the Plains - it was finally mentioned in two discussions but essentially after it had arrived. Similarly, TS Frank has yet to be directly mentioned in any FDs from Tucson.