Tuesday, February 19, 2013

Tomorrow's Weather Event

Tomorrow's event looks to be another one where the inflow of low-level moisture is limited. The graphic above is from yesterday's early WRF-GFS run at Atmo. Shown is forecast precipitation through midnight tomorrow night (Wednesday February 20th). The same forecast from this morning's early run is shown below. Across eastern Pima County the trend in the forecasts is toward lower rainfall amounts at low elevations and increased snowfall at higher elevations.


Currently, precipitable water (PW) is limited for this system. Shown above is blended PW from CIRA at Colorado State University valid at 5 am MST this morning. There is a band of moisture across the southern 2/3rds of Baja, where PW values are around an inch (brighter blues).  Here in southeast Arizona the final results for this event may depend upon whether this moisture to the south is pulled northward ahead of tomorrow's cold front.

The early WRF-GFS from this morning forecasts the cold front and main rain band to be crossing the Tucson metro area between 9 and 10 am tomorrow morning (below). The forecast surface plot below is valid at 10 am MST - looks like a very raw morning with cold rains over the city. The current WRF moves only one major rain band across eastern Pima County, with the event ending by early afternoon. Will check back on the low-level moisture situation and the new 5 am model runs later today.

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