Unusually warm start to April

[April 20, 2010]  Summer-like temperatures prevailed across central and southeast Illinois for much of the first half of April. Temperatures averaged 10-15 degrees above normal through April 15, with several days seeing highs in the 80s and lows in the 50s. These readings were more typical of mid- to late June! Normal highs for early April are in the upper 50s and lower 60s, while lows are typically in the upper 30s and lower 40s.

The reasons for the extended period of warm air residing over the Midwest are complex but basically result from a "blocked" weather pattern that allowed high pressure at the surface and aloft to set up across the nation's midsection. Several days of southerly to southwesterly winds allowed warm air to move into the region, and plenty of sunshine acting on relatively dry air produced further warming of the air mass.

While it was very warm, few individual daily records were established. A record high was tied in Springfield on April 6 at 85 degrees.

The most unusual aspect of this warm stretch is its duration. Many locations in central and southeast Illinois were more than 10 degrees above normal for 12 of the first 15 days in April, while several days were more than 20 degrees above normal.

[National Weather Service, Lincoln office]