Monday, October 17, 2011

Taking A Look From The Northeast To The Southeast

A couple of things are of interest this morning - with one that will affect southeastern Arizona.
As a 500 mb trough to our north (vorticity maxima over the Uinta Mountains early this morning) digs to the southeast over the next 48-hours, several things attend the deepening system. First, a strong, surface, cold front is advancing down the Front Range of the Rockies. This front (see 1800 UTC surface plot above) already extends into extreme northeastern New Mexico. It should be affecting Tucson, as a backdoor front from the east, around sunrise tomorrow (see this morning's NAM 850 mb forecast valid at 1200 UTC tomorrow morning - below). The NAM model forecasts the backdoor portion of front to be even more pronounced on Wednesday morning, as serious amplification of the 500 mb trough occurs over the central U.S.

The deepening system over the central U.S. extends into the Gulf of Mexico on Wednesday morning, after kicking out the large area of disturbed tropical weather currently near Yucatan - a threat of heavy rains over the Southeast and Florida as this happens later today and tomorrow. The strong, surface, cold front is forecast to push southward all the way across the GoM.

Although it is early in the cool season for this to happen, the model forecasts indicate that cool air will push southwestward, crossing the Isthmus of Tehuantepec (see map above) by 48-hours. The land bridge of this isthmus reaches an elevation of only 735 ft. When continental cold fronts push this far south, the cold air funnels through the terrain gap, producing strong northeasterly winds out into the Pacific - these can be a serious hazard to fishermen and sailors. The 48-hour forecast from the GFS model (below valid at 1200 UTC 19 October) indicates such an event is imminent. Cold fronts such as this can also produce strong wind events in the Vera Cruz region, as cool, stable air is trapped and forced around the east end of the high mountains to the north-northwest.

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