Grim outlook for summer drought in Kentucky

Back on March 31 I posted here about the potential for a summer drought based on the developing La Nina and I used some statistical information to show that the amount of precipitation that occurs over the winter is not necessarily a good predictor of summer rainfall. However, now that meteorological spring is officially in the books (Mar-May), it is possible to show that 2007 is very likely to be among top 30 driest years since 1895 according to past history.

Dating back to November 1st, 2006, Bowling Green has a rainfall deficit that is approaching one foot. In fact, the period February – May 2007 ranks as the 3rd driest such period in over 100 years (9.66 inches) behind only 1941 (8.75) and 1918 (9.19). In fact, of the ten years where Feb – May rainfall was less than 11.00 inches, eight of them occurred prior to 1941, which further shows how rare it is in recent history to have such a dry spring. Using historical information from the Midwest Regional Climate Center, I looked at where the ten years with the driest Feb – May periods ended up ranking with regards to yearly precipitation. The results were not pretty.

Year | Feb-May prec. | Annual precip.
1941 | 8.75 | 15th driest
1918 | 9.19 | 9th driest
2007 | 9.66 | ???
1901 | 9.72 | 3rd driest
1900 | 9.77 | 29th driest
1934 | 9.82 | 8th driest
1930 | 9.90 | 1st driest
1926 | 10.72 | 98th driest
1985 | 10.79 | 22nd driest
1905 | 11.00 | 7th driest

Aside from 1926, which incidentally went on to have the wettest Aug-Dec period (35 inches) on record, all of the other years that started with a dry Feb-May period were among the driest 30 years of the past 100 years, including 5 of the 10 driest years.

This soil moisture anomaly map here shows the developing problem. The baked-dry soil in TN, AL, MS and GA means that any wind from the south (Gulf of Mexico) will have a lower humidity than normal, which means that when the air gets here it will be warmer and drier than normal, which is why I expect KY will have no problem reaching the 100 degree mark a few times this summer.

Obviously, the amount of precipitation that occurs in June will be important. Of the ten driest Feb-May years mentioned above, June was the biggest indicator of the ensuing summer drought. Those years that had at least 4 inches in June recovered and saw their drought conditions either improve or remain at a moderate level. Those years that had less than 4 inches (notably 1901 and 1930) saw drought conditions worsen into a severe drought. The outlook for the next two weeks is not promising. The Climate Prediction Center (CPC) has a large “hot and dry” bullseye right over the mid-south for both the 6-10 day and 8-14 day periods.

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