8:45PM

Yes, it can reach 80 this time of year. It can even reach 90. In fact, one year ago today, Boston’s high temperature was 90 – a preview of the very hot summer of 2010.

You may have heard chatter on the news and net about “80s” on Monday in the Boston Area. Not so fast. This time of year, the ocean waters surrounding New England are still very chilly. The water temperature in Boston Harbor is in the lower to middle 40s right now. The waters just south of New England and Long Island may not be quite as chilly as that, but are still fairly cool. And both of these may be working against record warmth in eastern Massachusetts on Monday. In fact, I will venture to say now that Boston’s high temperature on Tuesday will be warmer than that of Monday. Why am I confident of the weather 4 and 5 days out? I’m not. At least not significantly. I am just aware of what can and often does happen this time of year, so I’m cautious to check myself into the record warmth camp right now. I think when it comes down to forecasting Monday’s high temperature for Boston (and most of eastern MA), we have to watch 2 things: 1) Does the warm front even push through far enough to not come back as a back-door cold front to significantly cool the East Coast of MA? and 2) even if we get into the warm sector, will the wind be too much from the south, transporting ocean-influenced air from south of  New England up across southeastern New England including Boston, keeping high temperatures down from what they would be if the wind was more westerly, off the warm land? Either or both of these may come true for parts of the region, so we’ll have to see how it plays out.

In the mean time, we have a nice stretch of weather underway, and our frosty dawn on Thursday morning was followed by a sunny day with light winds and pleasant temperatures. Friday will be similar, as high pressure building overhead will promote chilly temperatures to start, with areas of frost, sunshine during the day, and generally light winds, except a better chance for a more widespread sea breeze developing during the day. The sunshine will probably become filtered as high cloudiness from a disturbance passing to our south fans up across the sky.

High pressure will hold strong on Saturday, with a sunny, milder day. The coast may still remain on the cooler side, however, thanks to another developing sea breeze.

A disturbance passing by on Saturday night may result in a few scattered rain showers, but most areas should remain dry.

Sunday, warmer air moving in above us will result in more cloudiness. Another round of showers, this one possibly more widespread, should hold off until late day or evening.

Monday should be a warmer day in most locations, but there are uncertainties, as noted above. I’ll try to nail down what I think is going to happen as we get closer, but for now, don’t count on any 80s near Boston.

A couple troughs and a cold front will pass the region from west to east between Monday night & Tuesday night. This will likely result in a few rounds of showers, and may mean that Tuesday is quite a mild day, as the cooler air will probably reside behind the final frontal passage. This is a slight change in thinking from yesterday, when I thought we had a shot of ending up with a northeasterly flow and much cooler air sooner. But it’s several days away, so there is plenty of time to figure this out as well.

Detailed Boston Area Forecast…

TONIGHT: Clear. Frost likely. Low ranging from around 22 in the deeper valleys to near 32 along the coast. Wind calm.

FRIDAY: Sunshine, filtered at times by high cloudiness. High 50 to 55 except cooling back into the 40s at the coast. Wind calm early then E up to 10 mph.

FRIDAY NIGHT: Clearing. Patchy fog in deeper valleys where areas of frost are possible as well. Low 30 to 35 inland valleys, 35 to 40 elsewhere. Wind light variable.

SATURDAY: Sunny. High 60 to 65 except cooling back through the 50s near the coast in the afternoon. Wind variable up to 10 mph with coastal sea breezes.

SATURDAY NIGHT: Variably cloudy. Slight chance of passing rain showers. Low 43 to 48. Wind light SE.

SUNDAY: Mostly cloudy. Chance of showers late in the afternoon or at night. High 55-65 coast to inland. Wind SE 5 to 15 mph.

MONDAY: Partly sunny. Low 45 to 55. Highs 55 to 65 coastal areas, 65 to 75 inland areas.

TUESDAY: Chance of showers. Lows 50 to 60. Highs 60 to 70.