Despite the disgustingly humid weather earlier in the week the temperature failed to reach 90 degrees. That got us wondering when the first 90-degree day usually arrives, so we dug into a mountain of climate statistics to plot the date of the first 90-degree day at Belvedere Castle for each year since 1876. The earliest 90-degree day was the 97th day of the year in 2010 (April 7th), while the latest was day 207 (July 26th) in 1877. That's a spread of more than three months!
The average date over the whole period of record is June 2-3 (two calendar dates because of leap year), but that does not tell the whole story. For the first 50 years of observations the first 90-degree day occurred, on average, on June 11-12. In the most recent 50 years that first day is May 27-28, or about two weeks earlier. The variability in the first date is very high so the earlier date may not mean much in terms of climate change.
More fun first 90-degree day facts: The first 90-degree day occurs most frequently on the 172nd day of the year, which just happens to be today in a leap year or tomorrow in a regular year. The temperature has reached 90 degrees 78 percent of the time by June 21st. Looking at the ten day forecast it appears that we won’t see 90 degrees until July. That hasn't happened since 1985 and has only occurred 17 times since 1876.
As for the rest of the forecast, a large high pressure system over northern Quebec will keep all the head and humidity well to our south for the next several days. Look for mostly clear skies with highs in the upper 70s to lower 80s and lows in the mid 60s through Tuesday. The next chance of rain will be on Wednesday.
Finally, for all you druids out there, the summer solstice is at 6:51 tomorrow morning.