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Posted at 12:48 PM ET, 04/03/2012

March “madness” out, normal spring weather in

After torching the record books in recent weeks, the weather pattern is now beginning to push temperatures back towards normal all across the country.

This change is particularly notable in the Great Lakes and Northeast, where during the past few days, temperatures actually dipped below average in many of the big cities. Freeze warnings covered northeast Ohio and western Pennsylvania last night, and frost advisories were in effect early this morning just west of the I-95 corridor from the suburbs of D.C. to New York City.

Temperatures compared to normal over last week (Regional Climate Centers)
Temperatures averaged over the last seven days are within 5 degrees (F) of normal (yellow and green shading) north of the Mason-Dixon line, as shown in the circled area in the image above.

Even in the middle third of the country, where temperatures just yesterday rocketed to 90°F near Kansas City just two days removed from their warmest March on record (+14.2°F for the month), temperatures are starting to slip. KC’s highs will likely hold in the 70s today, with cooler weather to follow this week. And on the heels of an east wind from Lake Michigan, Milwaukee only made it to 40°F on Saturday. Ouch!

Yet the temperature recalibration promoted by this new pattern isn’t a cool-down everywhere. Many places in the West have yet to see Spring really kick in. So a return to climatology for them triggered by the new weather mode is, in fact, a warm up.

Take for example, Seattle, WA. The daily-mean temperatures at Sea-Tac have been cooler than normal more than three-fourths of the days since mid-February, with highs in the 40s and 50s throughout March. And both San Francisco (SFO) and Los Angeles (LAX) have recorded below-average temperatures two out of three days for the last 6 weeks.

If the chill wasn’t enough, to add a little gloom to the West’s otherwise chilly picture, it’s been downright wet there, too. As CWG reported yesterday, Portland, Oregon and Spokane, Washington, had their wettest March on record.

So, for nearly everyone from coast to coast, temporary changes are coming, if not already underway. The pattern shift discussed last week is on schedule.

Upper-level ridging (warm air aloft) has recently become established in northern latitudes of the Western Hemisphere, replacing cooler air and strong westerly winds that for much of last month occupied those same regions.

High-altitude temperatures and winds for next week predicted by ECMWF model. Red shading indicates anomalous ridging/warm-air aloft (Penn State)
As we move through the upcoming weekend and into early next week, the global weather models suggest high-altitude ridging will indeed settle over the West (red shading in the image to the right), while a northwesterly jet stream across the middle part of the country (black arrow) separates it from much cooler temperatures aloft (blue colors) in the East.

In terms of sensible weather during this period, this should translate to a few warmer days in the West, and perhaps even a period of below-normal temperatures in the eastern third of the nation (highs in the 50s and 60s from New England to the Carolinas by the middle of next week). Though this setup will probably begin to break down sometime near the middle of the month, Mother Nature has for now suspended its blistering assault on climatology and is instead giving everybody a real taste of “normal” early Spring.

By  |  12:48 PM ET, 04/03/2012

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