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Posted at 12:38 PM ET, 06/19/2012

Fierce heat focused on Plains to make brief appearance East

Even though summer doesn’t officially start until tomorrow, parts of the nation that don’t often bake this time of year have already experienced impressive heat.

Kansas City, for example, hit 97°F just yesterday, and has racked up 12 90-degree days so far this season. So has Chicago. Minneapolis, MN has reached the 90s as many times (5) as Raleigh, NC and Washington, D.C. and more times than Atlanta (4).

Meanwhile, other parts of the country farther east, have seen a wide variety of weather outcomes recently. Over the Northeast, most of the time it was relatively cool, with daily maximums only in the 60s and 70s.

As we move forward through the end of June, this basic theme will continue. Much of the Northeast will get a couple more shots at the 90s during an otherwise average to cooler-than-average regime, while places in the mid-continent will continue to roast, and perhaps accumulate 100-degree days much earlier than usual.

Jet stream flow (yellow arrow) for tomorrow, from the GFS ensemble mean. (Penn State)
One of those short-lived heat spikes for the East is now on its way. Highs will reach the 90s from Maine to the Gulf Coast this week. Many spots in the heart of this broad zone in the lee of the Appalachians, from Boston southward to D.C., should peak in the upper 90s on Wednesday and Thursday.

The weather pattern associated with this setup is not particularly complicated over the Lower 48. A southwesterly jet stream flow from the Rockies will get the hot weather to the East Coast. This upper-level wind pattern (to the right, above) should sustain the 90s along the entire the Eastern Seaboard through Thursday, and for another day or so from the Carolinas on south.

Temperature departures from average for next Tuesday, from the GFS model. (
But as we move through the weekend, cooler and less humid air will begin to target the Northeastern quarter of the country, with a multi-day period of below-average temperatures likely moving in early next week (blue shading to the right).

In tandem with this cooler shift in the East, a reinforcing shot of hot air will move over highly populated regions of the eastern Rockies, and the central and southern Plains. That will continue the more or less continuous stretch of nearly rain-free 90-100°F temperatures already in place, perhaps through the rest of the month.

Upper level maps for next week show a powerful upper ridge right over the mid-continent.

Jet stream flow for next Wednesday, from the GFS ensemble mean. (NOAA/ESRL)

Current soil moisture anomalies (millimeters of water). Reds and yellows indicate drier than average conditions. (CPC)

Underneath this mountain of heat (see above), temperatures will soar to levels not usually seen so early in summer.

Unfortunately, this part of the country is already experiencing drought conditions, and there is not much hope for significant rain there in the next 1-2 weeks at least.

In fact, the lack of soil moisture there right now (yellow shading in image to the right) will positively feedback on the pattern and tend to make rain less likely and the hot air mass even hotter. It seems as though a pattern change capable of meaningfully deflating the Plains ridge, if one does come this summer, won’t arrive before July.

By  |  12:38 PM ET, 06/19/2012

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