Midwest to Mid-Atlantic Bracing for Onslaught of Heat

By Andrew Freedman

A wide swath of the U.S., from the Midwest to the Mid-Atlantic, was bracing for the onslaught of another heat wave Monday and Tuesday as high temperatures approaching triple digits was in the forecast for cities like Minneapolis, Milwaukee and Chicago. The heat will expand into the Ohio Valley and Mid-Atlantic through midweek, before a strong cold front sweeps cooler air into those regions. 

Maximum heat index forecast for Wednesday, July 18, 2012. Click on image for a larger version. Credit: NOAA.

Heat warnings and advisories were in effect Monday in Minnesota, South Dakota, and Wisconsin, as well as for the Philadelphia and New York City metropolitan areas, where heat indices were expected to hover near or above 100°F on Monday and Tuesday. According to the National Weather Service, record high temperatures may be set in Minnesota on Monday. Minneapolis has already had two days of 100°F heat so far this month.

You can track record temperatures using Climate Central’s Record Tracker.

The Mid-Atlantic and Carolinas may experience heat indices of 105°F to 110°F on Wednesday. On Tuesday, Washington D.C. may see its sixth day of triple-digit heat this year.

By late in the week, warm conditions are expected to settle on the High Plains and South Central states, areas that have already broken numerous heat records for the summer. Much of Kansas, Oklahoma, and Nebraska will likely see highs in the 100s all week. 

Guy Walton at The Weather Channel, using data from the National Climatic Data Center, reported that during June and July, to date, there were 902 monthly record high temperatures set or tied — an extraordinary amount for such a short period of time. 

By comparison, there were just 114 monthly high temperature records set or tied during all of June and July 2010, and 315 monthly records set or tied during all of June and July 2011.

U.S. Drought Monitor as of July 10, 2012. Click on image for a larger version. Credit: NOAA/USDA.

While natural variability plays a leading role in short-term weather and climate patterns, studies show that manmade global warming favors more frequent and intense heat events. A study published in 2009 found that the ratio of daily record high temperatures to daily record lows is becoming increasingly skewed in favor of record highs. The study found that rather than a 1-to-1 ratio, as would be expected if the climate were not warming, the ratio has been closer to 2-to-1 in favor of warm temperature records during the past decade (2000-2009). This finding cannot be explained by natural climate variability alone, the study found, and is instead consistent with global warming. When you look at individual years, the imbalance can be even more stark. For example, through late June 2012, daily record highs were outnumbering record daily lows by a ratio of 9-to-1. 

The heat this week won’t come anywhere close to rivaling the heat wave that struck from mid to late June through early July, but it will serve to add to the country’s mounting drought woes, since hot temperatures hasten the drying of soils. 

On July 11, the U.S. Department of Agriculture issued its largest natural disaster declaration on record, making farmers in 26 states eligible for federal assistance. 

A new federal report on the 2012 drought will be released on Monday, and is expected to show that the drought now ranks among the top 10 most intense and widespread droughts in American history, according to reporting by The Weather Channel. 

Given the ongoing hot weather in the Midwest and the Plains, combined with a lack of widespread rainfall in the forecast, it’s likely that the drought will only intensify during the coming weeks.