From the NWS in Indianapolis...
May 2007 has started out mild and very dry in Central Indiana. The precipitation total during the first 18 days of May 2007 at the Indianapolis International Airport has been a mere 1.07 inches. This is well below the normal value of 2.50 inches for the first 18 days of May. The average temperature for these first 18 days of May has been 67.6 degrees, slightly more than 5 degrees above normal.
So what is the reason behind this dry and mild start? The jet stream, which would typically be over the nation’s mid-section during May, has been displaced farther north. A ridge of high pressure has been present for most of the month across the Midwest, which has shifted the track of low pressure systems (and their rainfall) well north. When cold fronts have approached the area, the high pressure has held them at bay, and the sinking air associated with a high pressure system also acts to dry the air out. The end result is an extended period of sunny and dry weather.
This May marks the driest start to any May in the Indianapolis Area since May of 1992 when the first 18 days brought only 0.88 inches of precipitation. That month finished out with just 1.56 inches of rain, making it the 16th driest May on record. ?wfo=ind
