Complicated Setting Today

The surface front that I've been writing about the last few days appears to be coming into play here a bit sooner than I'd anticipated. This will make the evolution of the day quite dependent upon the timing and the strength of the downslope flow between here and the Continental Divide.

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The Tucson morning sounding (top graphic) continues to have a pathetic vertical wind profile, and this morning's NAM progs don't improve it much during the coming 18 hours. It also appears that CAPE has diminshed considerably, because of the somewhat dry layer from 850 to 700 mb - and this before we'd try to figure out what part of the sounding is too moist (comparision between GPS and sounding PW shows the sounding more than 3 mm too wet).

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Middle data plot is surface chart for 1400z this morning. A large area of 24-hour pressure rises of more than 15 mb was present from north-central Nebraska southwestward across eastern Colorado, with max rises right at 20 mb around Pueblo. It appears that the front may have just passed Demning, New Mexico, at the time of the plot, meaning that it is about to come over the Divide. There is a large cloud mass covering almost all of New Mexico this morning, and extending into southeast Arizona.

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The bottom chart is the NAM 850 mb forecast for midnight tonight. The forecast indicates that by that time the front has pushed westward across almost all of southern Arizona. With strong downslope winds occurring across southeast Arizona. The NAM forecasts strongest winds in the troposphere to be the near-surface, post-frontal winds - not at all a good shear setting for organized storms.

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Thus, my first look at the morning data leads me to conclude that things will not quite manage to come together to produce a big storm day locally. However, the positives I do see are that there does appear to be a weak piece of the shortwave trough moving westward across southern Arizona and that the steering winds do become northeasterly, albeit very light. the timing of the front is of course very critical and probably the factor that will dominate today's weather outcomes.