DAYS 1-5 (AUGUST 14-18)
Will it rain? Will it not rain? If it rains, how much will it rain? Questions without answers. Well we have some answers, but not all of them are complete or confident, but we’ll get to that. First we have a beautiful Sunday to enjoy before our weather pattern takes a turn. Today’s weather is brought to you by Canadian high pressure and brings us lots of sun, a chilly morning compared to recently, but a nice rebound to near normal afternoon highs with low humidity. It’s interesting to note that this morning’s 7:00 a.m. temperatures showcase some of the regional / local differences you can have. Boston, for example, is exhibiting the urban heat island effect with 65 while a typical cool spot, Norwood, sits at 53, just a few degrees above the upper 40s. Meanwhile, out on the islands, ocean water keeps Nantucket modified at 68 while the relatively low elevation air port at Martha’s Vineyard sits at 54. These are the types of things a forecaster has to take into account when they need to get very specific with temperature forecasts, and it’s often easy to forget and have certain areas outside your temperature range, even if the forecast was “generally” good. Anyway, nice day today, and then the change begins Monday, slowly though, as high pressure slides offshore. As a broad area of weak low pressure begins to expand slowly northward along the US East Coast, we’ll first notice some increase in cloud cover, though the humidity rise will be hardly noticeable at first. It’s the Tuesday-Thursday period when we will have our highest humidity and a greater threat of some rain in the region. The model guidance is now all over the place with rainfall amounts – with the 3 models I mentioned yesterday having kind of flip flopped overall, ranging from a tenth of an inch of rain (European model) to a more moderate rainfall event (GFS model’s 06z run after a heavier one on the 00z run), with their colleague the Canadian model getting fancy with a heavier rain event for northeastern MA and southeastern NH while the rest of the region is left out, having just light rain. What does this tell you? It tells you that the guidance is not very helpful for this event just a few days out from it. But since Tuesday is day 3 on a Sunday morning update, and it looks like the main event, whatever that turns out to be, will be Wednesday to early Thursday, I can’t say I’m surprised. To be fair, while not a winter pattern, the set-up of the surface features looks a little like what you see in a colder season storm (just not as strong) so the configuration of that pattern and exact placement of features will be key in determining just how things unfold. So another day must go by before I really try to nail down details, and for now I am going to go with a light to moderate rain event for Wednesday, ending Thursday, and adjustments will be made as necessary.
TODAY: Mostly sunny. Highs 77-84, coolest coast. Dew point 50s. Wind variable up to 10 MPH with light coastal sea breezes.
TONIGHT: Mostly clear. Lows 55-62, warmest urban areas. Dew point lower 50s. Wind variable up to 10 MPH.
MONDAY: Sun and high clouds. Highs 78-85, coolest coast. Dew point upper 50s. Wind SE up to 10 MPH.
MONDAY NIGHT: Mostly cloudy. Lows 60-67. Dew point upper 50s. Wind SE up to 10 MPH.
TUESDAY: Mostly cloudy. Chance of showers, favoring the South Coast. Highs 72-79, coolest coast. Dew point 60+. Wind E 5-15 MPH.
TUESDAY NIGHT: Mostly cloudy. Chance of showers. Areas of fog. Lows 61-68. Dew point 60+. Wind E up to 10 MPH.
WEDNESDAY: Cloudy. Rain likely eastern MA, RI, and southeastern NH. Chance of rain elsewhere. Highs 68-75, coolest coast. Dew point around 60. Wind NE 5-15 MPH, higher gusts possible in coastal areas.
WEDNESDAY NIGHT: Mostly cloudy. Chance of rain. Areas of fog. Lows 55-62. Dew point lower to middle 50s. Wind N 5-15 MPH, higher gusts.
THURSDAY: Mostly cloudy with a chance of showers in the morning. Sun/cloud mix afternoon. Highs 75-82. Dew point 50s. Wind NW 5-15 MPH.
DAYS 6-10 (AUGUST 19-23)
High pressure brings fair and warmer weather with manageable humidity for August 19 through the August 20-21 weekend based on current timing. Humidity increases along with a shower/thunderstorm chance early the following week as high pressure shifts off the Atlantic Coast.
DAYS 11-15 (AUGUST 24-28)
Overall trend is for weak westerly to southerly flow with limited rain chances and near to above normal temperatures. Still don’t see a pattern that brings consistent enough rainfall to do a lot of drought reduction.