NewsJuly 6, 2012

Ongoing Heat Wave in U.S. Rivals Events of Dust Bowl Era

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Andrew Freedman

By Andrew Freedman

Tens of millions of Americans continue to sweat out one of the most intense heat waves on record since the Dust Bowl era of the 1930s, with heat watches and warnings in effect yet again from the Plains to the Mid-Atlantic states. As happened during the Dust Bowl, the heat is helping to dry soils, increasing the extent and severity of drought conditions across the country and threatening this year’s corn crop. 

During the past 30 days, a stunning 6,439 warm temperature records were set or tied in the Lower 48 states, including 240 all-time warm temperature records. For the year-to-date, warm temperature records have been outpacing cold temperature records by a lopsided 7-to-1 margin.

NOAA visualization showing high temperature from July 3 to July 7, as forecast by a computer model. The brighter orange colors show temperatures higher than 100 deg F. Click on the image for a larger version.

In a long-term trend that demonstrates the effects of a warming climate, 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 global warming increases the odds of extreme heat events and may make them warmer and longer lasting.

The individual records set during the ongoing heat wave tell the story of how unusual this event has been so far.

One day after experiencing its hottest Fourth of July since 1911, on Thursday Chicago came within 2 degrees of its all-time high temperature record of 105°F, which was recorded in 1934. If Chicago reaches 100°F or higher on Friday, it will have tied its longest streak of 100-degree days on record, which was first set in 1911.

RECORDS SET OR TIEDHigh MaxHigh MinLow MaxLow MinLast 7 Days
(Jun 29 - Jul 5, 2012)2,1556863781Last 30 Days
(Jun 6 - Jul 5, 2012)4,2302,209747775Year to Date
(Jan 1 - Jul 5, 2012)23,28318,6383,4242,500

Source: Preliminary Data from NOAA

St. Louis is expected to tie its record for the second-longest streak of 100-plus degree days on Friday, equaling a record set in July 1936.

Thursday was one of the top five warmest days on record in both Madison and Milwaukee, Wis.

Madison reached 104°F on Thursday, which set a daily high temperature record and was the third-highest temperature on record for that location. The extreme heat came one day after Madison had its hottest July Fourth on record with a high of 102°F.

Madison also set a record warm minimum temperature on July 4, when the temperature failed to drop below 81°F. That tied for the fourth-warmest minimum temperature on record, and according to the National Weather Service, this heat wave could tie for first on the list of the longest stretches of consecutive 95-degree days or higher.

Milwaukee has already set a record for the second-longest stretch of 100-degree temperatures. It was so hot in Milwaukee on Thursday that National Weather Service employees attempted (and failed) to fry an egg in the office parking lot, noting that pavement temperatures weren’t quite hot enough.

Just across Lake Michigan, other areas have already seen heat rivaling the hot summers of 1988, 1934, and 1936. Detroit, for example, has already exceeded its annual average for 90-degree days, and it’s only early July.

Relief in the form of cooler air is in the forecast starting Saturday in the Midwest, and eventually making its way to the Atlantic Coast. However, before the cooler air arrives, the Mid-Atlantic and Carolinas can expect two to three more days of brutally hot conditions. Washington, D.C.’s all-time record high of 105°F may be threatened on Saturday, and triple-digit heat is possible in cities such as New York, Philadelphia, Baltimore, Charlotte, Raleigh, and Pittsburgh. Washington has already set a record for the longest streak of 95°F-plus degree days in 141 years of record-keeping, according to the Washington Post.

The latest heat wave comes after the U.S. experienced its warmest spring on record and warmest 12-month period, and follows an unprecedented heat wave during March, when thousands of heat records were also broken. The average springtime temperature in the lower 48 was so far above the 1901-2000 average — 5.2°F, to be exact — that the country set a record for the largest temperature departure for any season on record since 1895.

The warmer-than-average conditions are helping to expand drought conditions across the country, particularly in the Midwest and West. More than 50 percent of the Lower 48 states are now considered to be in some form of drought, with the worst conditions located in the West, where heat and drought are helping to fuel a deadly and unusually severe wildfire season.