Friday, July 09, 2010

Weather Discussion for 9 July 2010 - Southeastern Arizona

Brief summary of yesterday – bit more measured rainfall at high elevations yesterday from the mostly warm-top convection. The Pima County ALERT network had rainfall measured at 8 of 93 stations with 2 stations reporting slightly more than a 1/10th of an inch. Three of the RAWS stations had rainfall, with Columbine on Mt. Graham reporting 0.17”. Of interest was the occurrence of deep, cold-top convection further north in Mexico, with convective remnants dissipating over the far southern GoC during the night.

This morning – considerable cloudiness extends far to the west and into southern California. Easterly low-level winds continue, but there is a nice layer of south-southeasterly winds above 800 mb (see TWC sounding plot – note sounding is a bit dry [2.5 mm] wrt the GPS data) and these have acted to increase moisture substantially from 800 to 500 mb – quite an interesting change since yesterday morning. Dewpoints have increased 3 to 5 degrees F at the mountain top RAWS stations during this period, which is quite important. GPS data indicates that PW has reached values above 30 mm (see lower image) across southeastern Arizona this morning – which is also a positive factor. The westerly Pacific jet in upper-troposphere has shifted northward, leaving winds in southeastern Arizona L/V above 600 mb. It appears that convection will have some westerly component to its steering flow, at least through much of day (the morning NAM tries to bring this around to easterly by midnight). On the downside is the fact that the warm inversion aloft has strengthened some this morning – it is quite formidable in the sounding plot!

This afternoon and evening – looks like a definite continued upturn in convection today. The big question is whether we’ll see the development of deep, cold-top storms. This looks tough for the low elevations, unless some very strong outflows develop. However, conditions over the mountains are much improved today. I can come up with lifted parcel theta-w of 24C and possibly greater for the higher mountains, meaning there’s an excellent chance for much stronger, cold-top, storms over the mountains. Should be a much more interesting afternoon and evening, with better chances for strong outflows into lower elevations. To the south, the upper-level inverted trough will be moving across the lower half of the GoC, with a significant increase in strong convection in Sonora and Sinaloa. Pat Holbrook e-mailed yesterday that he thought there’d be a Gulf surge tomorrow. Given the likely increase in storms over and near the GoC next 24-hours, I think that he’s probably correct. Perhaps I’ll record the first rainfall of the summer here at house by Sunday evening – chances are certainly looking good.

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