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    It's Not Hot Everywhere

    7/12/2011, 6:59:54 AM

    Tuesday, 11:35 a.m.

    One of the main weather stories these days is the brutal heat in the middle of the country. Dallas is going for their 11th consecutive day of 100-degree heat, and Oklahoma City has already reached 13 days in a row of triple-digit heat. The streak appears likely to continue for a while longer in both cities.

    It has been hot in other places, too. In fact, most places from the eastern Rockies to the East Coast, and from border to border, are running above normal so far in July. You have to go to parts of Montana and the West in order to find places that are running somewhat below average so far this month. And they are about to turn even cooler.

    An upper-level trough has moved into the West once again, something that was forecast fairly well by the longer range computer models last week. Take a look at the upper-level forecast for this evening:

    This sort of rather intense upper-level low has been seen on numerous occasions the past two or three months. As another feature rolls over the top of the ridge that is way offshore and south of the Gulf of Alaska, look for this trough to be 'renewed' late in the week, with still another feature lurking in the wings over the northeast Pacific:

    The end result of this will be to turn temperatures even farther below average in the coming days. The GFS ensembles clearly portray this idea, as you can see here by its forecast for Friday:

    That's an awful lot of blue showing up west of the divide, and even though it is probably overdone on the extent of the cooldown, it will still be below average by a comfortable margin, especially in California and Nevada. Eventually it will heat up in the West, and stay hot, but probably not until late in July or in August!

    With the upper-level dome of heat more or less entrenched on the Plains, areas from Kansas on south won't be cooling down any time soon. In fact, with the ridge more or less flexing its muscles Friday into the weekend, expect the heat to expand back to the north, and more places are apt to reach 100 degrees at some point between Friday and Monday across portions of Nebraska, South Dakota, Missouri and maybe even Iowa. And the 90s won't stop at the U.S. - Canadian border, either!

    You would think that with that kind of heat out on the Plains, it's going to stay hot and maybe get even hotter in the East, right? Well, that's not going to be the case. In fact, it will go in the opposite direction starting tomorrow as a weak cold front makes steady progress through New England and the mid-Atlantic states. While there may be a hit-or-miss shower and thunderstorm across the region tomorrow, especially over upstate New York and northern England closer to the upper-level trough axis, and across the Virginias into North Carolina closer to the core of the heat and humidity, the main impact of all this will be to deliver a much drier air mass across the Midwest, then through the Great Lakes and on into the entire Northeast.

    A pretty strong high is building into North Dakota and Minnesota tonight. That same high will move into the upper Great Lakes tomorrow night, sending the cooler, drier air ahead of it, resulting in a much more comfortable night across Wisconsin and Michigan into upstate New York and parts of Pennsylvania. As the high slides farther east, it will mean lower humidity and cooler nights along the I-95 corridor late this week.

    The orientation of the high late this week and this weekend is one that doesn't lend itself well to allowing the heat in the Plains to come blasting eastward over the Appalachians into the East, either. Look at the forecast for Friday afternoon:

    Granted, cool is a relative term here. Nighttime lows will probably be in the 60s; some from Pennsylvania on north may wind up in the 50s. Not exact far below normal, but below it, nonetheless. And with average highs well into the 80s, it is harder to get above normal, especially well above it. With no westerly component to the wind in the mid-Atlantic, there's no way to make it much hotter. So, for a couple of days, you'll see some negative departures showing up. They may not be big, but most would probably agree it beats the relentless heat!

    Even the Southeast should end up in negative territory late this week into the weekend. How? Well, not so much from a frontal passage, but more because of the weakness in the upper-level flow over the East. It mean the air aloft isn't as warm as it had been. In turn, there will be plenty of low-level moisture around, so it will be easier to generate clouds along with showers and thunderstorms that should have the effect of keep temperatures near to a little below normal. I'm sure the Southeast will welcome that change, especially if it means rain!

    Tomorrow, I will look a little at the tropics, even though little is happening there. I'll also give you the opportunity to support me in my upcoming MS 150 bike tour!

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


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