Thursday 11:15 AM

The weak low pressure area that was in the eastern Gulf of Mexico yesterday has now crossed Florida and has a distinct circulation just east of the north Florida coast. As long as it is over the warm waters there, we have to watch for signs of development. But that's not the only challenge with this system. Will it run out over the Gulf Stream and then get whisked northeastward? Or will it hug the coast and bring drenching rain to the coastal Carolinas later today through tomorrow... and farther north later?

Meanwhile, the dominant feature for areas from Illinois to the Middle and North Atlantic states is a high pressure area centered over Pensylvania. It is establishing (east) and strengthening (west) heat wave conditions. Temperatures in the Washington to New York City corridor will experience afternoon temperatures well up in the 90s each day through at least Saturday.

On the north and northwest sides of the heatwave high pressure area, there is a front extending from northern New York State out to Wisconsin. A weak low pressure area tracking eastward along the front is helping to trigger thunderstorms from Minnesota to Wisconsin today. The strength of the low pressure area and its speed of advance will help determne how far south the frontal zone reaches tomorrow night and Saturday morning.

Yesterday, the GFS was suggesting the front would move south of Chicago while the NMM-WRF kept it north. On last night's runs, those roles reversed. At issue seems to be another low pressure area that will move into the central Great Lakes later in the weekend. The faster that system moves and the stronger it is, the less time the front will have to move south ahead of it. The storm itself could cause showers and thunderstorms over much of Lake Michigan Saturday night and Sunday. Obviously, this forecast situation remains challenging, and updates to the Chicago to Mackinac race weather story will address these issues. Please see http://www.accuweather.com/mackinac/ (ads on this site)

Farther east, thunderstorms developed in western and central New York this morning and those wll move east and southeast this afternoon before falling apart tonight. The NMM-WRF model has been suggesting these storms could survive as far south as central to eastwarn Pennsylvania and New Jersey, but other solutions keep the storms farther north. You can keep track of them this afternoon on our radar displays.

Posted by Elliot Abrams on Thursday, July 17, 2008 10:54 AM
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