DAYS 1-5 (JULY 19-23)
Today is a weather app lesson day. Your app (or perhaps your local media) has warned you about heat, but what about the details? What about the fact that overnight the wind switched slowly from east to north with a marine layer in place, including a great deal of lingering clouds, and fairly cool (and not too humid) air? That’s part of today too, and that’s how the day starts out. But as the wind switches to south and southwest during the morning, things change. The clouds (where they are) will be scoured away leaving a sun/cloud mix, and in will come the higher humidity with building heat for the remainder of the day, and we’ll reach our high temperatures for today from mid to late afternoon. But today is not going to be “the hot one”, or “hot ones” in this case. We have 2 of them coming, fitting neatly into the weekend. The specific high temperatures will depend on your location, and wind direction. I don’t think Boston makes 100 because I think the wind will be not west enough (read that as the wind will be southwest, not west) on Saturday, and by Sunday, when it is, the core of the heat will have passed just enough to again keep them under the century mark. Your ideal weather conditions to get 100 degree heat to the coast including Boston is a west or west northwest wind which comes down off the slopes of the hills to the west, compresses and heats up, but also dries out somewhat. So I’m going to forecast no higher than 96 Saturday and 97 Sunday for the airport itself. If you go back to places like the Merrimack Valley, then you have a much greater chance of seeing triple digit high temperatures. Remember that the news media is going to hit you with “feels-like” temperatures, which will indeed exceed 100 in many locations on both days, but that can also vary from person to person depending on your level of tolerance and your health, so instead of worrying if the heat index is 107 or 110, just take it easy, and do the things you know to do and have been reminded of a zillion times. You’re smarter than they give you credit for. Pardon my digression, but I feel it is important to say these things. Back to the weather… When does the heat break? Monday, probably with showers/thunderstorms as a cold front moves through. But some areas may be visited by a shower or storm late Sunday as well as the front will be approaching and making the atmosphere a little less stable than it will be beforehand. Our storm chances are limited to a low risk of an isolated pop up air mass storm late today and are pretty non-existent Saturday. There is a wild-card in forecasting at this time of year that can also have an impact on temperature reality vs. forecast, and that is debris cloudiness from upstream thunderstorm complexes that usually visit the upper Midwest, Great Lakes, and nearby Canada. One such complex, or the remains of it, may be diving through NY State early Saturday and spread some cloudiness into southwestern New England, but I don’t think it will get into the WHW forecast area to have an impact on temperatures. Another such complex may cross parts of northern New England Saturday night and toss some cloudiness into northern portions of the WHW forecast area early Sunday, but this also remains to be seen, depending on the details of any storm development out there, and something I can adjust for in future updates if needed. There has been some interesting things on guidance in the last several runs, with some models now bringing wet/cool weather into the region for Tuesday, instead of previously-mentioned dry and seasonably warm summer weather. I am not falling for those model runs at this time, and staying with the previous forecast.
TODAY: Mostly cloudy start, then partly sunny. Becoming very humid by midday on. Highs 80-87 Cape Cod, 87-94 elsewhere, occurring late day. Wind light variable becoming S to SW up to 10 MPH.
TONIGHT: Partly cloudy. Very humid. Lows 72-79. Wind WSW up to 10 MPH.
SATURDAY: Mostly sunny. Very humid. Highs 93-100, hottest Merrimack Valley, except 85-92 South Coast and Cape Cod. Wind SW 5-10 MPH.
SATURDAY NIGHT: Partly cloudy. Humid. Lows 74-81. Wind light W.
SUNDAY: Mostly sunny morning. Party sunny afternoon. Moderately humid. Highs 93-100, hottest interior valleys, except 85-92 Cape Cod. Wind W 5-15 MPH.
SUNDAY NIGHT: Variably cloudy. Scattered showers/thunderstorms possible. Moderately humid. Lows 63-70. Wind W 5-15 MPH, higher gusts.
MONDAY: Variably cloudy. Scattered showers/thunderstorms. Moderately humid. Highs 80-87. Wind W 5-15 MPH.
MONDAY NIGHT: Partly cloudy. Less humid. Lows 58-65. Wind NW 5-15 MPH.
TUESDAY: Partly sunny. Highs 78-85. Wind N 5-15 MPH.
DAYS 6-10 (JULY 24-28)
The upper ridge will have pushed back into the Upper Midwest and Plains allowing the jet stream to sink down over or south of the region and bringing more seasonable air to the region at midweek next week, but expecting mostly dry weather at this time. May have to watch a quick wave of low pressure around July 25 that may bring more cloudiness. Some increased heat and humidity possibly by the July 27-28 weekend along with a slightly better risk of a shower or thunderstorm at that time, but this is a lower confidence forecast this far out.
DAYS 11-15 (JULY 29-AUGUST 2)
Near to above normal temperatures expected with a couple opportunities for showers and thunderstorms as we say bye to July and welcome the arrival of August. The overall pattern will probably feature a weak westerly air flow with flat ridges of high pressure centered off the Atlantic Coast and over the Midwest.