IEM Daily Feature
Thursday, 14 March 2013

When does spring start?

Posted: 14 Mar 2013 05:33 AM

Yesterday's feature presented the end date of the coldest 91 day period of the year as a proxy for when spring starts. This was based on the daily climatology. The featured chart today looks at this metric in more depth. The top panel displays the past four years worth of trailing 91 day average temperature with the peak and trough labeled. The middle panel displays the yearly date of this minimum in 91 day trailing average (denoting the coldest 91 day period for the year). The bottom panel crudely displays the number of days during the "spring season, which is the number of days between the trough and peak minus 91 assumed days for the summer. So for this year and this metric, spring started on the 9th of March. The middle panel shows that this metric has not made it past the Ides of March since 1960! The bottom panel would indicate that our recent decade of spring seasons have been on the short side of long term trend.

Good = 20
Bad = 5

Tags:   spring