July 2011: Most extreme July on record for the U.S.

According to the National Climatic Data Center's Climate Extremes Index, July 2011 was the most extreme July on record (since 1910) with a value of 37%. The Climate Extremes Index is created by merging the various climate indicators (drought, flood, extreme heat, extreme cold, etc.) into an index that can be tracked over time. This month's record CEI was due to extreme warm minimum temperatures across the country, wet northern Plains and Great Lakes, extreme warm maximum temperatures, and the severe drought across the South and Gulf Coast.

It was the fourth warmest July on record for the nation, and the fourth warmest month overall with an average temperature of 77°F. Extreme heat continued to bake the South, and Oklahoma and Texas both had their warmest months on record. Oklahoma's statewide average temperature was a remarkable 88.9°F in July, which is the warmest monthly statewide average for any state in any month. Dallas, Texas hit or exceeded 100°F on 30 out of the 31 days in July. For the entire South climate region, which comprises Texas, Oklahoma, Kansas, Louisiana, Arkansas, and Mississippi, July 2011 was the warmest month on record for any of the climate regions.

As we noted in a previous blog, an unprecedented area of exceptional drought covered the United States in July, the largest area in the history of the U.S. Drought Monitor. 75% of Texas was in an exceptional drought, and the entire state of Oklahoma was in moderate to exceptional drought in July. The NCDC estimates that it would take 20 inches of rain to end the drought in one month in the worst hit areas of Oklahoma and Texas.


Figure 1. Texas and Oklahoma had its hottest and the state of Washington had its 11th coolest July on record last month, according to the NCDC.


Figure 2. Texas had its second driest July on record, and Oklahoma had its 9th driest according to the NCDC. California continues to be wetter than average, and last month was its 8th wettest July on record.

Angela