It’s a Broken Record of Record-Breaking Heat

Another day, another slew of temperature records set, as the extraordinary March heat wave shows no signs of completely abating. Along with the record warmth, Monday brought a line of severe thunderstorms that stretched in a line from the Texas-Mexico border to the U.S.-Canadian border in Minnesota. Thunderstorm wind damage was reported near Minneapolis, a city more accustomed to March snowstorms than thunderstorms. The presence of warm, humid air so far north was extremely unusual for this time of year, but then again, so is nearly everything else about this heat wave. 

In fact, the broad geographic scope of this heat event, along with the margins by which records are being broken, the time of year this is occurring, and the duration of the event are all indications that this may be an unprecedented event since modern U.S. weather records began in the late 19th century.

Surface temperature anomalies for March 12-18, showing the warmth over North America in bright orange/red colors. Click on the image for a larger version. Credit: NOAA/ESRL.

In Chicago, where temperatures have reached at least 80°F for a record five six days so far this month, another record was set on Monday, this time for the warmest low temperature, with a low of 61°F — which is warmer than the typical high temperature in the “Windy City” at this time of year. On Tuesday afternoon, Chicago reached 84°F 85°F on Tuesday, its highest temperature on record in the month of March.

Chicago tied its daily high-temperature record of 78°F on Monday as well, and temperatures are forecast to climb back into the 80s on Wednesday.

The National Weather Service forecast office in Chicago offered some perspective on the record warmth in a statement on its website:

“80°F warmth is not very common even in April . . . let alone early to mid-March. Chicago only averages about one day in the 80's in April each year. Only once in the 140 recorded years of weather observations has April produced as many 80-degree days as have been observed this March. That was set back in 1977 when eight days as the thermometer peaked above 80°F . . . 

“If the forecast for 2 more days in the 80's verifies, it would also would mean that 7-of-17 (roughly 41 percent) of Chicago's 80°F days in March, dating back to 1871, would have occurred in March of 2012.”

In Marquette, Mich., the weather has been warm enough to melt 4 feet of snow in two weeks, with little to no snow cover on the ground now — a rare occurrence for mid-March. The Great Lakes have also lost nearly all of their ice cover at a time of year when they are typically just starting to see a decrease from the winter peak.

Broad-scale weather pattern responsible for the heat wave in the Midwest and East. Click on the image for a larger version. Credit: NWS.

In northern Michigan, overnight lows have been running warmer than the typical daytime highs for this time of year, which are normally in the 30s to low 40s. Traverse City and Pellston, Mich., both set all-time March high-temperature records on Monday, with 83°F and 82°F readings, respectively.

According to the CapitalClimate blog, so far this month warm weather records have been outpacing cold records by a lopsided ratio of 19-to-1. Since January 1, the ratio has been closer to 14-to-1, the blog reported.

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. Other studies have shown that climate change increases the odds of extreme heat events and may make them warmer and longer lasting.

Minneapolis set another record high on Monday when the temperature hit 79°F, breaking the old record of 72°F, set in 1910. The city also set a record warm low temperature, with a low of 63°F. For historical perspective, the typical low temperature for March 19 is 25°F. Temperatures for the first 18 days of March are running nearly 14 degrees above average in the Twin Cities, and Minnesota’s many lakes are rapidly losing any remaining ice cover.

“The record early heat (and humidity) is awe-inspiring, but what I can't get over is this: usually the atmosphere “auto-corrects”: periods of unusual warmth are usually followed by cold spells as the sky floating overhead attempts to regain some sense of equilibrium. Not this month,” wrote meteorologist Paul Douglas on his Minneapolis-Star Tribune blog.

“I keep waiting for a real cold front to come screaming south of the border, but we may have wait a little longer (October?) This spring we have 2 speeds: warm and hot.”

Rainfall amounts during the past week in Texas, Oklahoma and western Louisiana. Credit: NOAA.

In a rare feat, the overnight low temperature in Rochester, Minn. on March 18 was 62°F, beating the record high for the date, which was 60°F.

Although the most intense heat has been centered in the Midwest, the Northeast has also experienced record high temperatures in recent days. On Monday, Boston, Hartford, Providence, and Worcester, Mass., all set daily high-temperature records. In Maine, Caribou recorded its earliest 70°F day on record Tuesday, and other records were set statewide.

Even the Southeast is getting in on the warmth, with Atlanta having tied its record for the most consecutive March 80-degree days.

Meanwhile in the central and southern Mississippi River Valley and Plains states, the slow-moving cold front is triggering severe weather and heavy rains today. Residents of northeast Texas and southeast Oklahoma are now suffering from whiplash after going from an epic drought to flash flooding, with the National Weather Service describing the situation as “a tremendous setup for heavy rainfall.” Damaging tornadoes were reported near San Antonio, Texas last night, and more isolated tornadoes are possible today in Texas and Louisiana.