90s on Wednesday? I Have a Beer Riding on it!

There’s no doubt temperatures will be warming over the next several days. The cool, onshore, southeasterly flow from this weekend will be replaced by a warm, westerly wind regime Tuesday.

Our computer models indicate quite a bit of warming aloft Tuesday and Wednesday but there is one potential fly in the ointment. Cold fronts typically move in from the northwest and bring down colder weather from Canada. This time of year, however, cold fronts can advance from the east. This is known as a backdoor cold front. These fronts originate off the east coast of New England in the cold Atlantic waters and can be a forecaster’s worst nightmare.

As a rough first guess for a temperature forecast meteorologists like to look at temperatures at 850 mb or roughly4500 feet. On Wednesday temperatures warm up to nearly +16ºC at about at 850 mb. Some computer models, like the normally superior European, show 850 mb temperatures of over +20ºC! To put that in some perspective, during Connecticut’s worst heat wave in the last 100 years (July 19-21, 1991) the 850mb temperature only peaked around +21 or +22ºC!

With all that in mind it’s unclear just how warm we’ll get. This is how the NAM (North American Mesoscale Model) depicts surface winds Wednesday afternoon. The lines with arrows on them are known as streamlines. Streamlines are parallel to the wind so over Connecticut you can see northerly winds or winds blowing from north to south.

Over eastern Massachusetts winds are blowing from east to west straight off the ocean. The backdoor cold front is over Worcester and the Connecticut/Rhode Island border. Behind the front the winds are off the ocean and ahead of the front the winds are off the land.

Considering the Atlantic Ocean is only around 50º this time of year the wind direction makes a huge difference in the forecast temperature. Regardless of how warm the atmosphere is aloft wind off a cold ocean will drop temperatures very fast. Figuring out when the front moves in makes all the difference.

So the question becomes how quickly does the backdoor front make it to Connecticut. If it hangs back and moves in late Wednesday (like the Euro and NAM show) Wednesday will be very hot. Possibly as warm as 93º or 94º at Bradley Airport. If the front moves through in the morning or midday like the GFS is showing temperatures will struggle out of the mid 80s.

My forecast is for 90º at Bradley. In a situation like this the Euro and NAM are typically superior models. My colleague, friend, and fantastic forecaster Gil Simmons at WTNH disagrees. Here’s a twitter conversation we had earlier tonight.

@ryanhanrahan: Forecasting 90 on Wednesday. Early summer!!
@gilsimmons: I’ll wager on less than 90…….
@ryanhanrahan: Backdoor comes too late. Euro and NAM are torching us… 90F at BDL. High bust potential though 🙂
@gilsimmons: 5 bucks LoL
@ryanhanrahan: how bout 1 beer?
@gilsimmons: sounds good.

Who will be right??????? We shall see!


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