It’s May 9th and snowing! “Yes, Pittsburgh is in the upper-20s. That will make it the 8th time in our climate records that Pittsburgh has observed temperatures below 30 degrees in the month of May.” (source: National Weather Service (NWS) Pittsburgh). But still not as bad as May 9th in 1966 when Pittsburgh got 3 inches of snow! I took in the figs since I had moved them out of the basement last weekend.
Out of curiosity, a few weeks ago I looked up the Pittsburgh McKeesport Airport (closest official NWS station to where I live) data for the past 30 years to get a sense of when the last freeze and frost generally is. The further into spring you get, the less likely it is to have a freeze or frost. The NWS nicely lists the probabilities for “historically, there has been a 90% chance of it being this cold after this date” from 90% all the way down to 10%. I graphed the data and came up with:
I’m assuming freeze is 32 F or below and frost is 36 or below. I also fit a 2nd order polynomial but honestly as today has showed (freeze on 05/09 when the graph snows a near zero probability of that happening), there are plenty of outliers. Anyhow, I thought the data was interesting and depending on my risk tolerance lets me guess when to put out my plants (in conjunction with a 10 day forecast!).