Today is the first day of meteorological summer or the start of the warmest three months of the year. Unfortunately if you were expecting warm weather, it’s not going to happen for a few days.
A look back at May:
May ended on cool, wet note but only in the final few hours. Overall it was a dry and very warm month. This year Boston had 19 days of 70-degree weather or higher. This is the second-highest number in the record books alongside three years where there were 20 such days. Back in 2005, a cool May, only three days reached 70 degrees. Boston’s data for May 2015 is below.
The last eight days were particularly warm. The average high temperature of 82.3 degrees was higher than the average for July! This was a highly unusual stretch of warm weather in the month of May. We finally are seeing some much-needed rain, but it certainly waited until the final few hours of the month to fall. Prior to yesterday, many climatological sites in southern New England were about to set a record for their driest or second-driest May. Now, this will end up in the top 20 driest Mays, which is still dry but not as dramatic.
June starts cold and wet.
We have about 36 hours of cool wet weather to go before things become more typical for June. The coldest high temperature recorded for June 1 in Boston was 53 degrees. If Boston only reaches 52 degrees, which is possible, this would make this the coldest June 1 high temperature on record. As I have often said, weather in New England is about extremes, and the averages don’t mean very much. Take the warmth of Saturday and the chill of today, add them up and divide by two, and that’s close to the actual average for this time of year.
Why so cold?
The reason for the chill is basically due to the wind direction that dramatically shifted yesterday afternoon. After reaching the upper 70s to almost 80 degrees on a southwest wind, a flow of air off the cold Atlantic brought chilly marine air rapidly south into the area. The jet stream had been stuck in a configuration, which kept warm and dry weather here and wet weather over Texas and Oklahoma. This looks to have shifted for now.
The weather map above shows the front stalled to our south. Overnight and into Tuesday, small waves of energy will ride along this boundary and bring more rain to the region. The radar prediction for Tuesday morning indicates showers, and some heavier downpours are again possible.
This will slow the morning commute and continue to add water to the ground which was becoming very dry.
Even with significant rain now, rivers are so low they could handle many more inches of rain. Here’s a chart for one spot on the Charles River in Dover. Notice how far below flood stage this area is currently.
I suspect on Thursday, when the next drought monitor is issued, we will see some official improvement in the status of the drought. As of 7 a.m. Monday, much of the region has seen 1 to over 2 inches of rain. You can see some of the data below.
The extended forecast indicates a return to temperatures in the 70s and a few chances of showers over the next 10 days. I don’t see any total washouts, but also the drought-like pattern seems to have broken for now.
Once we get into June, it becomes increasingly less likely to see an all-day rain as most of our precipitation falls from showers.