Another Precipitation Event For Southeast Arizona

All of the models are now indicating a nice (mostly rain except at highest elevations) precipitation event for Arizona through midweek this week. This occurs as a short-wave trough at 500 mb swings in from the Pacific, shifting the current moisture plume south and eastward. Amounts will be lightest down here in the southeast. The models have so far been way too wet in northern and northwestern Arizona, but a significant precipitation event appears likely for central and northern mountain areas as the deep moisture plume from the Pacific (see earlier posts about this feature) moves across the state. The event is likely to be focussed around Wednesday evening here in southeast, although timing and the exact track of the vorticity maximum varies in the different model forecasts.

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Top figure shows the ECMWF forecast, from the operational version, that is valid at 5 pm on Wednesday (22 December 2010). The model forecasts a nice band of deep moisture extending well south into northwestern Mexico.

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Middle figure shows the operational NWS GFS forecast of accumulated precipitaion valid at 5 am on Thursday morning - with the southeast to northwest gradient of amounts very pronounced, as with last week's event.

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Bottom figure shows output from the U of AZ Atmo run of its WRF-GFS model from midnight last night. The image is of model forecast radar composite reflectivitiy at 5 pm on Wednesday afternoon, indicating two bands of showers moving across southeastern Arizona. The model forecast indicates that 3 or 4 bands of showers could move across the Tucson metro area before this event ends.

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Once again, it will be interesting to watch how the details of this event actually evolve during the next three days.