Wednesday, February 23, 2011

Apparently February 2011 Will End With Its Second Very Cold Weather Event

The forecast models have now been in reasonable agreement for several days (although the NAM seems to be holding with a different alignment of the west coast, short-wave at 500 mb) and indicate another very cold weather system will dig into the Southwest this weekend (500 mb temperatures within this developing wave were colder than -40C last evening over much of Alaska and northwestern Canada). Thus, it appears that February 2011 will exit just as it began, with unusually cold temperatures and perhaps a better chance of precipitation this time (snow right in town?). This event will likely garner more attention - the Tucson Rodeo is underway and runs through Sunday. The big dollar, PGA Match Play Championship comes to Dove Moutain just north of Tucson beginning this morning and running through Sunday afternoon. The most important matches are scheduled for the weekend, and there will be substantial national TV coverage of the event - could be quite interesting!

The two graphics above compare the operational member 500 mb forecasts from last evening's ECMWF and GFS model runs. Note the runs are very similar and forecast 500 mb heights to fall below 540 dm over the Southwest by Saturday afternoon. The ECMWF is about 6 to 12 hours slower than the GFS, but both models are forecasting a very cold weather system across Arizona over the weekend.

The two panels above show the operational GFS forecasts for midnight on Saturday night. Although the GFS height contours at 500 mb indicate a cutoff, the model winds indicate a strong open wave with excellent forcing for upward vertical motion. The operational member of the GFS forecasts 1000-500 mb thicknesses falling toward 528 dm during the Saturday night. If the thickness falls this low, with precipitation occurring (as the model forecast indicates), then the snow levels would drop right into metro Tucson. Note that all 12 GFS ensmble members forecast precipitation across southeast Arizona for the 12-hours ending Sunday morning at 5 am, and 9 of the members forecast precipitation for the 12-hours ending 5 pm Saturday afternoon. February 2011 could end up having record-setting storms twice during the month! Our visitors to Tucson (with expensive match play tickets) could leave shaking their heads, wondering why the PGA picked this cold locale for one of their biggest tournaments - keep tuned (matches will get lots of coverage on NBC).

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