Day 178: A Pattern Change

Posted by pmarsh on 27 Jun 2010 | 0 comments

With most meteorologists talking about Tropical Storm Alex, you are probably wondering why tonight’s image is a radar mosaic of the United States and not something relating to Alex. Actually, my image tonight does relate to Tropical Storm Alex. The thunderstorms depicted in the radar mosaic are developing along a cold front that is slowly moving southward across the United States. This cold front marks the leading edge of a mid-troposphere trough that is beginning to be carved out across the eastern part of the United States. This trough is replacing the ridge that has been entrenched across the central United States for the last few weeks. As I mentioned in the Day 173 post (linked above), a large ridge over the central United States is not conducive for a tropical wave to enter the Gulf of Mexico. However, a large trough over the eastern United States is conducive. Thus, the trough beginning to replace the aforementioned ridge will allow Tropical Storm Alex to turn toward the north. The all-important question then becomes, “How far north will Alex move?” The answer to this lies out west and is dependent upon what happens with the mid-troposphere pattern. Currently, a large ridge is developing / forecast to continue to develop across the western United States, coincident with the developing eastern trough. The bottom line: the weaker the ridge, the farther north Tropical Storm Alex will be able to move.