Sunday, February 22, 2015

Rain Before End Of Month?

Web cam shots at a bit after 7:00 am MST this morning show: above - some middle clouds and virga over the Catalinas and parts of Tucson; below - bright sunshine contrasts with shadows out at Kitt Peak.

As the west-east oriented short wave at 500 mb moves southward, there is some increased middle level moisture moving across southern Arizona this morning. However, as this feature moves slow across the Southwest values of PW will actually be decreasing. Primary impacts of this system, which has at best weak forcing for vertical motion, will be orographic precipitation at higher elevations from southern California eastward across Colorado. Graphic above is from 00 UTC WRF-NAM forecast on the 5.4 km grid and shows accumulated precipitation through 5:00 am on the 25th. Graphic below is from 06 UTC WRF-NAM on 1.8 km grid and shows forecast of PW valid at 11 pm MST on the 24th - DRY. Other WRF variants forecast similar outcomes, but some have very light precipitation falling at the highest elevations of southeastern Arizona. So, some measurable rain in the gauge here looks like a long-shot for coming few days - but models have been very unstable this year and I'll keep watching.

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