Friday, 11:20 AM

If you get a chance, check out the Springfield, Missouri radar. Here's a kink to it:

http://www.accuweather.com/radar-local.asp?partner=accuweather&zipcode;=&level;=local&type;=sir&site;=ksgf

This is a classic mesocyclone, or meso low as we often call them. A fairly small low pressure area that is packing a massive punch, and there is a tremendous amount of wind associated with it. This is turning into a derecho, a long-lived damaging wind event. one that will lay waste to a large portion of the southern half of Missouri.

It won't stop there, as this is being fueled by a surge of very warm, moist air in the low levels of the atmosphere from the Gulf of Mexico--dew point temperatures to 70 degrees all the way up to southeastern Missouri as I write this. At 850mb, there's a strong southwest wind blowing a warm, saturated air mass into this complex, so as long as this low can maintain this line of supply, it will maintain itself.

I don't trust the modeling on this, as it waffles back and forth from one run to the next, and from one model to the next. But I'm pretty confident that it will be maintained across the middle Mississippi Valley and impact parts of many states, including southernmost sections of Illinois and Indiana, Kentucky, and maybe northernmost Tennessee this afternoon and evening. Then it will go across the central Appalachians and pound parts of and then across the Appalachians overnight and tomorrow morning, hammering southernmost Ohio and West Virginia into the northern half of Virginia and probably parts of Maryland before finally going off the coast later tomorrow. Along the way, there are likely to be numerous reports of wind damage, some hail and tornadoes, and certainly some flooding, with 2 to 4 inches of rain likely to fall in the heart of this zone.

This isn't the only system on the weather map today. There are two others of note that will have an impact on the weather from the northern Plains to the Northeast. The first of these is really rather minor, and because of all the storminess plowing across Missouri and over the middle Mississippi Valley right now, there won't be much left for this disturbance to work with as it crosses the eastern Lakes, the northern Ohio Valley, and the rest of the Northeast this afternoon and tonight into tomorrow morning. Yes, there will be some showers and a few thunderstorms, but no flooding downpours, and very little severe weather, if any. Again, it's the lead system of two, and it will be working in a relatively warm and moist environment, but without all of the 'super juice' farther upstream.

The second disturbance is actually a beast, one that will likely produce some potent thunderstorms ahead of a strong cold front as it crosses into and through the Midwest late this afternoon and tonight. Specifically, parts of southern Minnesota, central and southern Wisconsin, northern Iowa, and northernmost Illinois will see the impact of this system through tonight.

Late tonight and tomorrow, the surface low that becomes a part of this will cross the Lakes and head into Upstate New York, and it will bring rain and some powerful thunderstorms through Michigan into Upstate New York, eventually even into parts of northern Ohio and Pennsylvania late tonight into tomorrow. There will likely be some severe weather, especially where it concerns damaging winds and hail.

It will be interesting to watch the 'synergy', if you will, between these two feature. My read on this is that the mesocyclone will move off the mid-Atlantic coast fairly well intact before noon tomorrow, taking most of the rain and thunderstorms offshore with it. In fact, I feel pretty confident that it will dry the mid levels of the atmosphere out out enough so that west to southwest winds kick in and promote sunshine. With strong winds aloft, those will get mixed down to the surface, and that should mean temperatures making a quick run at 80, even in places that get pounded overnight and early tomorrow morning by the meso low.

At the same time, there is probably going to be a sympathetic burst of showers and thunderstorms farther north with the approach of the northern stream disturbance and the surface storm associated with it. The cold front will lag behind by a few hours, but it how much moisture will be left to work with? Not a lot, so tomorrow afternoon and evening, there will probably only be spotty convection across the mid-Atlantic and into southern New England ahead of and with the cold front.

Then the storm will race across northern New England late tomorrow night and early Sunday, driving the cold front offshore. There will be plenty of moisture wrapping around the north and northwest side of the storm, though, so look for a lot of clouds hanging back behind the low along with some rain showers. That will impact Wisconsin into West Michigan tomorrow, and the eastern Lakes into upstate New York and maybe northern Pennsylvania late tomorrow night into Sunday, and then New England later Sunday and Sunday night.

While you'd think that would end the threat of severe weather, it probably doesn't. Instead, it's likely to just shift it farther south and maybe slow it down a little bit. For instance, on Sunday, this front is likely to stretch from the Red River Valley on its western end to the Carolinas on its eastern side, and somewhere in between there's likely to be some strong thunderstorms. Yet another upper level disturbance coming out of the Rockies and across the central Plains will be the trigger mechanism, trying to pull some of that warm, humid air across the Gulf Coast region back to the frontal boundary.

This will turn into a wave of low pressure, albeit a weak one, that will traverse the Tennessee Valley and the Gulf Coast region Monday and Monday night, effectively pulling that cold front to the I-20 corridor. This will wipe out the above normal warmth there, and certainly bring the night time lows back to normal, if not below.

There will be another surge of warmth coming from the Southwest and out of the southern and eastern Rockies out onto the Plains early next week, but little of that warmth will probably ever be seen across the Great Lakes into the Northeast and mid-Atlantic states, certainly for no more than a day. Why? Still another strong cold front will enter the fray from western Canada, and this will mean another outbreak of showers and thunderstorms coming across the central and northern Plains into the Midwest later Tuesday into Wednesday.

Hmmm...what wonderful timing! I'll be in Chicago for a few days starting Wednesday, and that day I'm supposed to be a part their 'Moody Golf Outing.' I hope that if it rains, they don't blame it on the meteorologist!

Posted by Joe Lundberg on Friday, May 08, 2009 11:11 AM
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