A look at weather extremes and the big-picture climate connections.

Heat Wave Across Much of U.S. Marches On

The tale of two countries in the U.S. continued Thursday, with a cold, stormy West and an extremely warm Midwest and East. In fact, as heavy snow and rain fell in the mountains of the Pacific Northwest, the March heat wave continued to break records farther east. The early onset of summer-like weather has moved up the peak bloom of Washington, D.C.’s famed cherry blossoms, given allergy sufferers an unwelcome jump start to the allergy season, and is putting an abrupt end to the Midwest's ice fishing season.

When the warm weather pattern finally breaks sometime at the end of the month or in early April, it’s possible that tens of millions of Americans will have experienced the most extreme and prolonged March warm spell on record.

There were 400 daily high-temperature records set or tied on March 14 alone, along with 177 record-warm overnight low temperatures. This compares to just 20 cold high-temperature records, and one lonely record-cold overnight low - set at Pima Peak, in southwestern Arizona.

A computer model forecast issued on March 15 for temperature departures from average across the U.S. and southern Canada on March 19. The large area of warmer-than-normal temperatures is seen as the big red-and-white region across the Central and eastern U.S. and parts of Canada. Click on the image for a larger version. Credit: Ryan Maue/policlimate.com.

Between March 8-14 there had been 1,201 daily high-temperature records set or tied, and 634 record-warm overnight lows. This compares to just 155 cold-high temperature records and 63 record-cold overnight lows. This comes out to a ratio of about 8-to-1.

In a long-term trend that has been found to be inconsistent with natural variability alone, daily record-high temperatures have recently been outpacing daily record-lows by an average of 2-to-1, and this imbalance is expected to grow as the climate continues to warm. According to a 2009 study, if the climate were not warming, this ratio would be expected to be even.

Some of the records set yesterday included Chicago, where the Windy City had its first 80-degree high in the month of March since 1990. The temperature hit 81 degrees F yesterday. Traverse City, Mich., broke its record for the earliest 80-degree reading on record. The previous record was March 27, 1945.

Trends in cherry blossom bloom dates. Credit: Brad Johnson/ThinkProgress.

Minneapolis has set a high temperature record every day for the past five days. Wednesday, it was 73 degrees F, a whopping 33 degrees above average. As meteorologist and Star Tribune blogger Paul Douglas wrote, last year there was six inches of snow on the ground on that date.

The forecast during the next week calls for continued record warmth in the Upper Midwest, Great Lakes, and the East, with some areas reaching temperatures up to 35 or 40 degrees F above average for this time of year. Plants are responding to the warm weather by blooming early. In D.C., where the annual Cherry Blossom festival draws tourists by the busload each spring, the National Park Service has moved up the peak bloom period to March 20-23, about a week earlier than their previous estimate. This is not quite as soon as the earliest peak bloom on record, which occurred on March 15, 1990, according to Washington Post’s Capital Weather Gang blog

According to Brad Johnson of ThinkProgress, the cherry blossoms have shifted their average blooming time about 10 days earlier in the last 90 years.

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