We were starting to encounter too many conflicts in April, especially with Brandywine Creek State Park.  1st Sat in April is Trout Fishing, which complicates early morning access (the park people won't leave the gate open for us), 2nd Sat is Kite Day so we can't have the pavilion (started this year).  Other than park issues, we like to avoid Easter which is usually in April, and the ETE takes away potential volunteers from WTC participation in the annual Christina Cleanup, again, always in April. 

Weather is notoriously variable at that time of year - we have had it both cold and miserable, and also too warm, in April, so we felt a couple of weeks earlier would not make much difference.  ETE was traditionally held in mid March until about 15 years ago, with no major problem thru' 30+ prior years, until one major snowfall caused postponement and the decison was made to move it later.   

Joan March