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    Less Volatile Pattern Ahead, But No Less Fascinating

    7/27/2012, 6:14:18 AM

    Friday, 11:00 A.M.

    Severe thunderstorms ripped across portions of the Ohio Valley into the mid-Atlantic and southwestern New England yesterday, cutting into what had become a very hot and sticky day:

    There will be more severe weather this afternoon from parts of the Ohio Valley into the East, as the air mass remains quite warm to downright hot and humid, but with the air aloft arguably cooler with an upper-level trough in the process of being carved out. Once we get into the weekend proper, further cooling aloft will be very limited, so with more clouds around, the opportunity for severe weather will become much more limited.

    Take a look at the NAM 50 mb forecast for tomorrow evening:

    The upper-level ridge is in no hurry to break down over the western Plains and eastern Rockies! If anything it is going to be a bit farther south than it has been, which means the northern Plains and northern Rockies may not be as hot as they have been at times of late, while at the same time it should be drier in much of Texas to allow for some modest warming over recent days.

    If you look more carefully at that image, you'll also note the strong upper-level ridge over the Atlantic. That feature is also not likely to change much in the coming week, so in between the two ridges there will be, by default, some sort of mean upper-level trough over the East.

    This means there will be a pooling of moisture in the East with time. There will be so much drying from the north and west during the course of the weekend in the wake of a weakening cold front and the passage of an upper-level disturbance tomorrow. Eventually, the surface flow will come right back out of the south pushing the tropical moisture right back to the north over time. In turn, the risk of showers and thunderstorms will be notably higher early next week from the Southeast into the mid-Atlantic states, if not into New England.

    Meanwhile, back in the Plains, it's going to be hot. As in over 100-degree heat, stretching from Texas up into Kansas and perhaps even Nebraska on occasion, and expanding eastward back into Missouri and Arkansas. And therein lies an interesting challenge.

    The European model, with a good bit of support from its own ensembles, suggest that the trough in the East is relatively weak late next week, with a flatter flow across the northern tier of states. That would allow more warmth (heat) farther north and east in the Thursday to Saturday and even Sunday time frame. In contrast, the GFS backs the western ridge to the Four Corners area. In turn, that allows for greater troughing in the East, and more cooling. Look at the GFS ensemble forecasts of temperatures next Friday for instance:

    That's an awful lot of cooling in a pattern that just hasn't been cool for a long, long time, especially in the Midwest and back into the eastern Plains! I am on the bandwagon of the European model these days, as it has been a far more accurate predictor of the amount of heat in recent weeks. Maybe this time it will be wrong, but given the past history since the middle of June, I rather doubt it.

    Still, this is what makes the forecast going forward so fascinating! Subtle upper-level differences in timing or placement of features can mean very large differences on the ground. And that's where we all live and breathe, making it all the more important to get it right. It'll be fun to watch next week, that's for sure.

    I will again make my request for help on the lengthy bike ride I will be a part of, the Keystone Country MS 150. A number of you have been so generous in the past, and I cannot tell you how much that means to me! The easiest way to lend your support to the Multiple Sclerosis Society is through a secure, online donation. And here's the quick link to do so:


    All you have to do is enter my name and my state (Pennsylvania), and go from there! I'm looking forward to riding with over 500 other bike enthusiasts who are all on board with raising support to help find a cure for MS! Thank you!

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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