DAYS 1-5 (JUNE 23-27)
Much has been said about the severe weather threat for today, but it’s important to stress this, so it’s understood. The greatest threat for severe weather (i.e., thunderstorms capable of producing damaging wind, large hail, and isolated tornadoes) exists in the northwestern portion of the WHW forecast area – southwestern NH and north central MA, as the eastern extension of the higher threat area which extends further into NH, VT, and much of western MA, as well as adjacent eastern NY. Timing and atmospheric conditions are less favorable for severe storms further east and south, but that’s not to say a few areas cannot see strong to even severe storms. The chance is just less likely in the bulk of the WHW forecast area. Now, let’s rewind several hours to now, and go forward. As I write this discussion at about 8:00 a.m. Sunday morning, a downpour is occurring outside my window here in Woburn MA, one among a cluster of them, a few containing thunder, and follow-ups to some overnight activity too. These are associated with the frontal boundary that came through on Friday as a back door cold front, and is now returning as a warm front. Where it’s not raining at any given moment, it’s overcast and there may be fog, due to the saturated air in place. So our day starts out quite dank, but as the front pushes through, the shower threat drops off for several hours, and we break the clouds and start to add more sun to the mix, making the temperature go up as the humidity remains high. So we’ll be in for a summery feeling day, and some of this will aid in the development of thunderstorms later. Starting about mid afternoon, we’ll have to watch for isolated storms reaching central MA and southwestern NH. It is from this point through early evening that the greatest chance of severe storms exists. Further east, there can be isolated to scattered pop-up showers and storms, but as previously mentioned, the severe weather threat is less. We’ll have to watch to see if any more organized clusters or small lines of storms can form, because these can create their own momentum in the form of cyclic regeneration with the help of outflow boundaries. However, these would have less rotation potential and greater straight-line wind potential. Again, these still favor areas west of I-95 and later in the day into the evening, but as we get into the evening, at least weakened forms of these can make it further east. This takes places as a trough of low pressure, in this case a pre-frontal trough (trough of low pressure ahead of a cold front) makes its approach. This feature will pass by tonight, and until it does so, we can still see some scattered to isolated showers and storms, even after the severe weather threat has diminished. Monday, the cold front will sweep through the region, and it’ll be a little colder aloft with a trough up there swinging through. While there will be less moisture to work with, there can still be and probably will be some showers and storms firing up. While I’m not looking for too much in the way of severe weather, an isolated storm or two can be capable of hail and a damaging wind gust Monday afternoon to early evening. Finally, it all departs Monday night and this leads us to a great early summer day on Tuesday as high pressure builds in with warm, dry conditions. High pressure then slips offshore and Wednesday is a very warm day with some increase in humidity. A progressive pattern brings the next frontal boundary across the region sometime Wednesday night or Thursday, based on current timing, but this system looks like it will only bring a short-lived shower and thunderstorm chance, leaning toward late Wednesday night / early Thursday right now…
TODAY: Cloudy with areas of fog and scattered showers / thunderstorms with briefly heavy rain until late morning, then breaking clouds and partial sun by midday into afternoon, with isolated showers / thunderstorms possible by mid afternoon, favoring areas west of the I-95 belt, and late-day stronger storms possible favoring north central MA / southwestern NH. Highs 75-82 South Coast, 82-89 elsewhere. Dew point rises to around 70. Wind SE to S up to 10 MPH until late morning, shifting to SW and increasing to 10-20 MPH with higher gusts midday on. Damaging wind gusts can occur near any thunderstorms.
TONIGHT: Variably cloudy. Scattered showers and thunderstorms in the evening, with the potential for a few strong to severe storms favoring areas west of I-95 and especially west of I-495 and north of I-90. A few lingering showers and thunderstorms possible but diminishing overnight. Areas of fog. Lows 65-72. DP 60s. Wind SW 5-15 MPH shifting to W and diminishing, but wind can be briefly strong and gusty near any storms.
MONDAY: Variably cloudy. Scattered showers and thunderstorms mainly late morning on. Highs 75-82. DP starts in 60s but a slow downward trend. Wind W 5-15 MPH, higher gusts, especially around any storms where wind can be more variable.
MONDAY NIGHT: Partly cloudy. An evening shower possible. Patchy ground fog in low elevations evening, dissipating overnight. Lows 56-63. DP falls below 60. Wind SW 5-15 MPH shifting to NW.
TUESDAY: Sun and passing clouds. Highs 78-85. DP upper to middle 50s. Wind NW 5-15 MPH.
TUESDAY NIGHT: Clear. Patchy ground fog. Lows 57-64. DP under 60. Wind W under 10 MPH.
WEDNESDAY: Mostly sunny. Highs 83-90, except cooler South Coast. DP rises back above 60. Wind SW 5-15 MPH.
WEDNESDAY NIGHT: Partly cloudy. Isolated showers and thunderstorms late evening / overnight. Lows 65-72. DP 60+. Wind SW 5-15 MPH.
THURSDAY: Variably cloudy with a chance of showers and thunderstorms int he morning. Partly cloudy in the afternoon. Highs 80-87. DP falls below 60 Wind NW 5-15 MPH.
DAYS 6-10 (JUNE 28 – JULY 2)
High pressure dominates the region during much of this time period, with a frontal boundary to cross somewhere mid period (estimating early July 30) when a shower / thunderstorm threat will be present. Temperatures near to above normal.
DAYS 11-15 (JULY 3-7)
Independence Day forecast period including the “Fourth of July Weekend” looks decent with a west to northwest flow and only 1 or 2 brief potential interruptions from passing disturbances / frontal boundaries in an otherwise mainly dry and seasonably warm pattern. More details to come…