Many in the Pioneer Valley woke to morning temperatures in the mid and upper 30s Tuesday morning, along with some low 40s in and around Springfield. A cool day followed as temperatures struggled into the low and mid 60s for afternoon highs, despite plenty of mid September sun.
With high pressure in control along with clear skies and calm winds we can expect good radiational cooling again tonight with the result being near record low temperatures in the low to mid 30s. A few upper 20s in the far outlying areas are possible, which of course will put an end to the growing season in those locations that do go below freezing. The record low for tomorrow morning is 30 in Springfield. We will come close but probably not make it that low in the city. The National Weather Service has in fact placed a Frost Advisory throughout western Massachusetts for the overnight hours and into about mid morning on Wednesday. As was the case last night, if you have tender plants outside bring them in if you can or cover them up for the overnight and early morning frost potential.
High pressure remains in control on Wednesday and after a really chilly start to the day temperatures do rebound into the upper 60s to low 70s in the afternoon. It will be another bright and sunny day, so overall a real nice day to be outdoors. Winds will go around to the southwest, less than 10 mph, bringing in the milder temperatures through the afternoon hours. Although another clear night follows Wednesday night the mercury does not fall as low as previous nights, with lows mainly in the 40s. A few upper 30s are likely in outlying areas. Light southwest winds overnight.
Thursday through Saturday present more spectacular weather in thanks to the dominance of high pressure. Clear nights and sunny days will be the rule through the period with a continued moderating trend that brings afternoon highs well into the 70s, overnight lows in the upper 40s to low 50s both Thursday and Friday nights.
Clouds do increase late Saturday and especially Saturday night as a cold front approaches. We could see a period of showers very late at night or Sunday into midday as the front moves through western Massachusetts at that time. Lows Saturday night close to 60, slightly cooler on Sunday, hovering around 70 degrees.
Speaking of Sunday the autumnal equinox officially takes place at 4:44 in the afternoon, meaning that Summer ends and Autumn begins.