I think you've got it right but said it wrong: 90% chance of being safe from frost after April 7. 10% chance of a late, light frost.
It might well go below 36F, but only one chance in 10 of a 32 degree frost.
I usually take April 7 or so as my 50% chance of frost date. March always gets to me, becuase we often have WEEKS of quite warm weather in February and sometimes even January. I've been feeling the warmth and getting over confiodent ... then like this year: more snow and frost in March than in Jan and Feb!
My ambition is to build some small, portable frames for little hoop tunnels. First use them to warm and dry the soil in some rasied beds, then shelter the seeds and seedlings so I can use all of the unsettled weather in march, plus some of February.
Who knows. maybe I'll find things I can overwinter in the ground under a little plastic. My Italian leaf broccoli just overwintered with no more care than my occasional words of awe and encouragement. Nice to have something dark green and helathy all winter!
