Dr. Jeff Masters on The Drought

Late February storms put only a slight dent in U.S. drought

Published: 4:14 PM GMT on February 28, 2013
Abundant moisture from heavy rains and snows that fell during two major Midwest storms in late February put only a slight dent in the great Midwest drought of 2012 – 2013. According to the February 28, 2013 Drought Monitor, the percentage area of the contiguous U.S. suffering moderate or greater drought shrank from 56% to 54%, and the area in the worst category of drought–exceptional drought–fell from 6.7% to 5.4% over the past week. These are the largest 1-week improvements in these drought categories that we’ve seen for 9 months and 15 months, respectively. The improvements were most noteworthy in Oklahoma, the Texas Panhandle, and the Southeast U.S., where drought improved by a full category (using the level 1 to 4 categories of the Palmer Drought Severity Index.) However, the dry pattern that has been dominant over the U.S. for most of the past year will re-assert itself during the coming ten days, and most of the drought region will receive less than 0.5″ of precipitation through March 9. There exists the possibility of a significant Midwest storm on March 10, according to recent runs of the GFS and ECMWF computer models, but it is too early to assess if this storm may be able to provide significant drought relief. In general, droughts are more likely in the Midwest U.S. when warmer than average ocean temperatures prevail in the tropical Atlantic, with cooler than average ocean temperatures in the tropical Eastern Pacific (La Niña-like conditions.) This is what we had in during most of 2012, and continue to have in 2013. Equatorial East Pacific ocean temperatures are currently 0.5°C below average. This is similar to the ocean temperatures seen in the spring of 2012, just before the Great Drought of 2012 began. Most of the U.S. drought region needs 3 – 9″ of precipitation to pull out of drought. Unless the Midwest receives a top-ten percent wettest spring on record, drought is going to be a huge concern as we enter summer.

Figure 1. Drought conditions as of February 28, 2013 showed that drought still gripped a majority of the U.S. Image credit: U.S. Drought Monitor.

Figure 2. Predicted 7-day precipitation for the period ending Thursday, March 7. Less than 10% of the U.S. drought regions are predicted to receive as much as 0.5″ of precipitation (dark green color.) Image credit: NOAA/HPC.

Jeff Masters

from:    http://www.wunderground.com/blog/JeffMasters/article.html