By: Chief Meteorologist Eric FisherBy Eric Fisher

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Wet, warm, and humid. If you had to guess a month of the year I’m talking about, it probably wouldn’t be September. The month typically thought of for dry air, sunny days, and the return of cool nights did not feature much of any those conditions. I wouldn’t call it a barn-burner but the constant mild nights helped this September to be one of the warmest ever recorded in Boston.

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Graphic: WBZ-TV

Overall, it wound up being the 4th warmest September on record. It was the third straight month to achieve Top 10 warmest status in Boston and the fourth overall this year. According to the National Weather Service in Norton, it’s the first time we’ve had 3 straight Top 10 warmest months since the spring of 2012.

Graphic: WBZ-TV

We had plenty of warm days, but it was the nights that lead the charge here. Nearly every single night of the month was warmer than average thanks to humidity and cloud cover. It was easily the record-setter for warmest overnight lows. This is a trend that shows up most clearly over the decades. A large warming signal in minimum temps with a more modest increase in maximum temps.

Graphic: WBZ-TV

As for rainfall, fugggedaboutit! We were soaked in September with several towns in the double digits for rainfall and a few even picking up over a foot. No easy task without a landfalling tropical system to bring in the high totals. I hope you turned the lawn irrigation off a while ago :-) We’ve been on a Tuesday cycle for weeks now. Each of the past few have produced flash flooding in parts of southern New England and the first Tuesday of October looks to do the same. On the plus side, it’s been an easy stretch for reseeding lawns with no cold overnight temps and plenty of moisture.

Rainfall over the past month. Source: Wx.Graphics

So the million dollar question – will it continue? It certainly looks like it for at least another couple weeks. We’re kicking off October on yet another stormy/wet note, and the pattern ahead largely supports warmer than average temperatures. The eastern U.S. ridge that has been so persistent since the end of June will stay in place over the next 14 days. In fact, it may amplify even more and come close to all-time record levels for the time of year as we head into next week.

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A strong ridge will likely build across the east again early next week with a corresponding huge trough with cold air in the west. But the ridge isn’t a slam dunk for summer temperatures here in New England just yet.

The main push of this next building ridge is early next week, but there are still some uncertainties at the surface. The pattern aloft looks like a complete torch, but there are still areas of high pressure trying to sneak across eastern Canada during this time. Which means we may end up in a similar spot to where we are now – a boundary right through southern New England with big warmth to the south and west but ocean winds and cooler temps pushing down from the north and east. It makes for a tricky call here locally.

If that boundary stays up across northern New England Sunday through Wednesday, we’re talking about an unusually warm stretch of 70s and 80s. Just a little shift in wind direction gives us 60s. It’s a little too soon to say for sure which side we will end up on in the Boston area. In general I find it’s not a great idea to go completely against climo (the averages and data over a long period of time)…and we’ve only had 4 straight days of October 80s in Boston once before – in 1947. We’ve had 3 in a row six other times. So *maybe* things will come together and give us a run of this exceptional warmth, but it’s far from a slam dunk at this point.

One thing that the constant ridging will very likely do is keep any anomalously cool air away from us through at least mid-month. Bottom line is that this means no frost chances through next week, mosquitoes hanging around, and a foliage season that is 1-2 weeks later than average. You can’t really delay the foliage much more than that because the main driver is the rapid loss of daylight we have this time of year. It doesn’t matter much if it stays really warm through Halloween…the leaves will still start to do their thing.

And good to keep in mind what ‘warmer than average’ really means at this point in the year. The daily averages are plummeting in October and so ‘warm’ becomes relative. Even now, anything in the upper 60s (or warmer) by day is above the average mark, and all nights that aren’t in the 40s are as well. By the end of the month, average highs are in the 50s. So while all the maps use red hot color schemes, it’s worthwhile to know what it means in the context of the month.

I’d say warmer than average is pretty close to ‘lock it in’ status for October as a whole. Will it be a top 10 month like the past several? It will largely hinge on what happens early next week. A string of days in the 80s would be enough to put us way up in the standings and hold off some cooldowns later on in the month. If it doesn’t materialize that high then we probably won’t finish near the top. Right now it looks like we may get a brief cooler shot mid-month before some rebuilding warmth to end October.


October temperature outlook from the Climate Prediction Center

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Eric Fisher