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Posted at 02:56 PM ET, 04/17/2012

Cool air coming back East late week; overall, quieter weather pattern

Now that one of the most-anticipated and feared tornado outbreaks in recent times is over, the pattern will calm down for a while. But that doesn’t mean it will be sunny and 75°F everywhere. The jet stream will soon change its shape from one that brought severe weather in the Plains and hot weather in the East over the past few days, to one that will dry out the mid-continent and bring chilly and showery conditions back into play east of the Mississippi.


The severe weather last Saturday in the Plains yielded 135 tornado reports. As shown in the image to the right, most of those (red triangles) were in Kansas. Interestingly, about 4 “tracks” stand out in the streaky distribution of the red dots, from northwestern Oklahoma to central Kansas.

Although we won’t know for sure until experts at the National Weather Service (NWS) and the Storm Prediction Center (SPC) finalize their post-storm analyses, it is possible that this outbreak was made up of a much smaller number of long-track tornadoes, where each one was reported multiple times along a lengthy cross-county transit.

Whatever the case may be, the risk for another severe weather outbreak anytime in the next week is low. Part of the reason is because the southwesterly winds at high altitudes that just yesterday helped produce lots of record highs in the Middle Atlantic and Northeast, including 87°F in Boston and 91°F in Trenton, NJ, are beginning to meaningfully change direction.


High-altitude temperatures and winds expected this coming Sunday. Blue shading indicates anomalous troughing/cool-air aloft. Yellow arrow identifies the jet stream. (Penn State)

Stormy weather that oftentimes flourishes underneath a southwesterly jet stream this time of year (just as it did last weekend) will be suppressed for a while, as those high-altitude winds (shown by the yellow arrow in the image to the right) begin to acquire a significant northwesterly component. Though this change won’t take place overnight, much cooler air (blue shading) will begin to filter into the Ohio and Tennessee Valleys late in the upcoming weekend.

By Sunday, highs will struggle to reach 60°F in Nashville, and yet remain in the 50s (at best) farther north over Cincinnati and Pittsburgh. And as the cool pocket of air settles in, a large area of disturbed, showery weather will likely envelop much of the eastern quarter of the country for a couple of days. In fact, some of the weather models produce accumulating snow in the higher elevations of the northern Appalachians during the weekend.


High-altitude temperatures and winds expected this coming Sunday. Blue shading indicates anomalous troughing/cool-air aloft. Yellow arrow identifies the jet stream. (Penn State)
By early next week, the northwesterly jet stream will help bring some of the chilly air all the way to the Northeast coast, just as that very warm air mass (red shading in the image to right) moves from the Rockies over the western Plains. I wouldn’t be surprised to see 90°F heat spread all across Kansas next week (20°F above normal), just as the big Northeast cities deal with a short, but rather unpleasant spell of 50s. And so it is, back and forth we go in a global weather regime that is struggling to lock on to any one particular mode over North America. It must be Spring.

By  |  02:56 PM ET, 04/17/2012

Categories:  Latest, U.S. Weather

 
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