Damp, mild, & volatile
So how did you like April 2011? I personally couldn’t complain. It wasn’t that hot and only occasionally chilly. In fact, the quick summary is slightly warm and slightly wet but occasionally volatile.
Temperatures ranged from 2-3F above the thirty-year (1971-2000) normal, and precipitation was almost a half inch over the normal. A tight precipitation gradient existed last month as the far western suburbs had more of a monthly surplus and folks toward the Chesapeake tended to be drier than the DC modest surplus. Our hottest day was Wednesday, April 20 with a nice 86 degrees and our coolest temperatures were hit on the 2nd and 6th of the month at 36F.
April certainly saw an interesting jet stream pattern over North America. A very large upper level cold pattern persisted over Canada, keeping very chilly conditions over our neighbor to the north. We would occasionally see some of that chill in our area, but typically not for long. That cold air supply in Canada and along the Northern tier of the U.S. kept North American snow cover above normal for the third of the past four years.
The contrast between the colder than average air over Canada and warmer than average air in the South intensified weather systems moving across the country, resulting in violent severe weather outbreaks - two of which impacted the mid-Atlantic region. The first occurred on April 16 when four tornadoes struck the region, and the second on April 27-28 with 11 tornadoes in the region.
The Richmond Times Dispatch reported with eight months to go, 2011 is already the second deadliest year for tornadoes in Virginia since 1950. The fifteen tornadoes that struck last week in Va. represented the fourth-biggest outbreak in the state in modern records.
Looking at April temperatures in a larger historical context, our average of 58.8F was 2.1F cooler than last year but on the upper end of the long-term range. It wasn’t until the early 1900s when we started seeing average April temperatures above 59F, and we have exceeded that level about four times in the past twenty years. April is a transitional springtime period and we can see considerable volatility in the month from year to year.
The National Weather Service publishes nice monthly assessments usually within a week of the close of each month.
You can click on your closest airport location here and the latest month should be available soon:
Historical Washington, DC data provided by NOAA and Speedwell Weather.
(CWG’s Jason Samenow contributed to this report)