DAYS 1-5 (JULY 16-20)
This weekend will give us not only very nice summer weather (not perfect) but also another lesson on the limitations of even our shorter-range guidance. As recently as yesterday, forecasts both here and around media called for a mostly sunny sky today, and while the sun will shine often today, it will also be filtered and dimmed quite often by a large shield of high cloudiness crossing our sky, born of convective activity in the Midwest. Also, some lower level moisture helped a bank of broken lower clouds form near the South Coast, which will dissipate as the morning goes on. But also, we have a little previously-not-really-detected-by-guidance disturbance that has to cross the region during the day today, and you’ll see evidence of that by cumulus clouds building up this morning into part of the afternoon underneath the high cloud shield. One or two of these clouds may grow large enough to release isolated showers. I would certainly not cancel any outdoor plans over this minor threat, but I would keep an eye on the sky just in case. That disturbance is gone later today and yet another one crosses the region tonight, keep the sky more cloud-filled than clear, and once again a spot shower can’t be ruled out, but it’s unlikely that any specific location will see one. The other change to the short term forecast is the ability to remove the shower and thunderstorm threat from the daytime and evening hours of Sunday – a day which will feature brighter sun than today, though still some clouds popping up to blot it out at times as well. Today’s humidity levels will be low enough to be deemed comfortable, but tomorrow’s dew point heads into higher territory, which will be noticeable. However, the more significant spike in humidity comes during Monday, especially in the afternoon, when a warm front crosses the region, preceded by a round of showers. Then a cold front approaches later in the day into the evening when a round of showers and thunderstorms is most likely. Advertisements of a widespread soaking rainfall with that system are probably over-selling the system’s capability to produce that. Now keeping in mind that even the short range guidance can struggle with these details, the tendency for quite some time now has been for the guidance to over-forecast the precipitation a few days out only to come back to reality as we get closer. That trend seems to be underway now, and while some heavy rainfall is certainly a strong possibility in the form of downpours / t-storms, a widespread beneficial rainfall would be one that would occur at a slower rate over a longer time, and I don’t see that as likely with that particular system. Behind it, we stay warm for Tuesday with a lowering of humidity and the return of fair weather after the chance of an early-in-the-day shower. A weak area of high pressure to the south of the region will provide fair weather into Wednesday as well, but since behind Monday’s system we’re not getting a shot of cooler/dry Canadian air that takes longer to kick out and modify, we’ll already be very warm to hot with more humid conditions again by midweek. At day 5, I can’t be confident of calling for a pop up air mass shower or thunderstorm Wednesday, but I won’t rule it out.
TODAY: Variably cloudy. Very slight chance of a passing shower midday to mid afternoon, favoring central and northeastern MA and southern NH. Highs 80-87, coolest coast. Dew point upper 50s. Wind S-SE up to 10 MPH.
TONIGHT: Variably cloudy. Lows 61-68. Dew point near 60. Wind S-SW up to 10 MPH.
SUNDAY: Partly cloudy. Highs 83-90. Dew point rising to middle to upper 60s. Wind S-SW up to 10 MPH.
SUNDAY NIGHT: Partly to mostly cloudy. Patchy fog. Lows 65-72. Dew point middle to upper 60s. Wind S up to 10 MPH.
MONDAY: Mostly cloudy. Showers likely midday through mid afternoon. Showers/thunderstorms likely late afternoon or evening from west to east. Highs 78-85. Dew point upper 60s rising to lower 70s. Wind S-SW 5-15 MPH.
MONDAY NIGHT: Variably cloudy. A chance of showers and thunderstorms. Areas of fog. Lows 62-69. Dew point falling slowly through 60s.
TUESDAY: Partly cloudy. Highs 83-90. Dew point near 60. Wind W 5-15 MPH.
TUESDAY NIGHT: Partly cloudy. Lows 63-70. Dew point near 60. Wind W up to 10 MPH.
WEDNESDAY: Partly cloudy. Highs 86-93. Dew point rising through 60s. Wind SW 5-15 MPH.
DAYS 6-10 (JULY 21-25)
Warm to hot weather July 21-22 with highest humidity and greatest chance of thunderstorms July 21 as a disturbance passes just to the north and drags a frontal boundary across the region, then a reduced storm chance July 22. Weak high pressure should keep shower and storm chances limited while we are warm to hot and have moderate humidity for the July 23-24 weekend and higher humidity again to end the period. This is not the classic Bermuda High set-up though as high pressure in the western Atlantic is to be weaker than one sitting over the east central US sending the hotter weather our way from the west southwest. We’ll actually find ourselves in a mean trough position here, albeit weak, so we end up with the warmth and see Canadian air masses unable to enter the region for a while.
DAYS 11-15 (JULY 26-30)
Unsettled weather episodes should be brief around the time of air mass changes, which will not be dramatic, as the overall pattern will be controlled by high pressure and a westerly to southwesterly air flow with mostly rain-free weather and near to above normal temperatures. We may get a push of drier air from Canada before the end of the period.