Vineyard Sound Marine Forecast
|Today...N Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft. A Slight Chance Of Showers This Afternoon.|
|Tonight...Ne Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Evening. Seas Around 2 Ft. Patchy Fog. A Chance Of Showers.|
|Sat...Ne Winds Around 10 Kt. Seas 1 Foot Or Less. A Chance Of Showers.|
|Sat Night...E Winds 5 To 10 Kt, Diminishing To Around 5 Kt After Midnight. Seas 1 Foot Or Less. Patchy Fog. Vsby 1 To 3 Nm.|
|Sun...S Winds 5 To 10 Kt. Seas Around 2 Ft. Patchy Fog. Vsby 1 To 3 Nm.|
|Sun Night...Sw Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Mon...Nw Winds Around 5 Kt. Seas Around 2 Ft.|
|Mon Night...S Winds Around 5 Kt. Seas Around 2 Ft. Patchy Fog. A Chance Of Showers. Vsby 1 To 3 Nm.|
|Tue...S Winds 5 To 10 Kt. Seas Around 2 Ft. Patchy Fog. Vsby 1 To 3 Nm.|
|Tue Night...Sw Winds Around 10 Kt. Seas Around 2 Ft. Seas Are Reported As Significant Wave Height, Which Is The Average Of The Highest Third Of The Waves. Individual Wave Heights May Be More Than Twice The Significant Wave Height.|
Area Forecast Discussion|
National Weather Service Boston/Norton MA
640am EDT Fri July 3 2020
A backdoor cold front will progress southwestward across Southern New England today, bringing clouds and cooler onshore flow. Showers and thunderstorms that could produce localized heavy rains are possible from midday through evening across western Massachusetts and western Connecticut. Mostly cloudy conditions early on the Fourth of July will trend mostly clear to partly cloudy by the afternoon, with temperatures still a bit cooler than average. Progressively warmer and more humid air invades the area next week with chances of afternoon/evening showers or thunderstorms each day. The best chance for storms looks to be Wednesday and Thursday.
Near Term - Until 6pm This Evening
Cloud areas in Eastern MA and Western MA/Western CT, mostly clear in between. No changes to the forecast.
Previous discussion... Today promises to be at least a meteorologically-interesting day across Southern New England - with several notable features that will drive our weather.
Early this morning, a broad area of surface low pressure was located just southeast of Ipswich Bay. Quite mild and continued rather muggy dewpoints are in place across most of Southern New England, with current temperatures generally in the upper 60s to mid 70s. This surface low is expected to shift southward through Cape Cod and into the adjacent southeastern waters by early this morning. A backdoor cold front was draped over western Maine, with a considerable field of lower stratus currently prevalent across much of ME (western extent currently extends to Portland). This backdoor front is expected to surge southwestward through the day today, with an increasing onset of lower stratus, enhancement to northeast onshore flow and cooler/more stable thermodynamic profiles across most of central and eastern sections of Southern New England. Finally to our northwest, embedded in NW flow aloft, several shortwave troughs will dive southeastward today. On the western periphery of the backdoor front into the CT Valley and the Berkshires, some greater destabilization should lead to the development of scattered thunderstorms by early this afternoon before the backdoor boundary eventually takes over.
The HREF appears to have the best handle on existing sky cover and position of the backdoor front. Following this, expect that most of northeast MA will become socked in with lower clouds shortly after daybreak, with lower clouds spreading southwestward into portions of Worcester County and much of RI by the afternoon. Greater prospects for diurnal warming further west into western MA/western CT, with little opportunity for much warming across eastern coastal MA. Opted for a modified non-diurnal trend basing highs on raw model temps today, with increasing NE winds. Showed highs in the low 70s across eastern MA, mid 70s central MA/much of RI and into the low to mid 80s in western MA/western CT before temperatures begin a steady fall.
Finally, the thunderstorm threat for today. Admittedly some uncertainty exists on how far east thunderstorms will extend. However there is good agreement in the convective-allowing models with enough instability, aided by upslope convergence and the western end of lift associated with the backdoor front, that heavier showers and thunderstorms should develop on the east slopes of the Berkshires by early afternoon. These storms then unzip southeast into the I-91 corridor by mid-afternoon before slipping westward into eastern NY where the better instability today should reside. There is a signal for training across parts of the Berkshires and the CT Valley, with tall-skinny CAPE profiles and PWATs (Precipitable Waters) 1.7". Though instability and shear profiles don't support a credible severe threat today, I'm concerned about the potential for localized hydro issues if a convective training signal materializes. Especially the case for the more urban areas like Hartford, Springfield and adjacent towns. Antecedent conditions don't support flash flooding, but given strong HREF probabilities for >1" rainfall over 3 hrs, it's not out of the question that urban/poor drainage flooding could develop as a worst-case outcome. Added heavy rain wording in the grids across our western counties to hint at the potential.
Short Term - 6pm This Evening Through 6pm Saturday
Models show lighter rains shifting southeastward into the more stable air later tonight across RI and into eastern/southeast MA and the Cape as the surface low shifts further southward into the offshore waters. Winds should take a turn towards the north as this occurs, with still considerable cloud cover across most of the area. Enough breaks in the clouds could lead to areas of mist or fog, with somewhat better chances across western locales with the wetter ground. A cool and cloudy evening with lows in the mid 50s north and west, to lower-mid 60s south and east.
Surface low will continue to pivot southeast of 40N/70W on Independence Day. More breaks in the clouds earliest in western MA and western CT, with considerable clouds across eastern MA and much of RI. However, sky cover even in eastern areas should start to trend more optimistically by the afternoon. Though most of the holiday should be dry, there is a limited risk for isolated showers or even a t-storm east of the Berkshires. As today, warmer temps to exist in the west where more sun supports highs in the mid 80s. Across central MA and RI looking at mid to upper 70s, and in the low to mid 70s across eastern MA and the Cape.
Long Term - Saturday Night Through Thursday
Big Picture... Northwest flow over the weekend with a shortwave moving through on Sunday. The pattern then becomes more zonal, with additional shortwaves moving through the flow. Consensus favors moving these shortwaves through on Monday and Thursday, but this timing can and probably will change with each model run.
Contour values at 500-mb are forecast near normal over the weekend, but trend above normal during the week. This indicates the deep- layer warms and supports a warming trend through the week except for any days we experience a cooling easterly flow at the surface.
Moderate confidence in the forecast.
Daily details... Saturday night and Sunday... Axis of high pressure from Nova Scotia settles south Saturday night, turning our low-level flow from easterly to southwest. Shortwave moves through the flow, supported by an upper jet from Canada that moves across Northern New England. The GFS is faster in moving this shortwave/upper jet through the northern areas, the ECMWF (European Centre for Medium-Range Weather Forecasts) slower. The airmass over Southern New England will be unstable Sunday, with CAPE of 500-1000 J/Kg, LI of -2 to -3. PW values (Precipitable Water values) will be around 1.25, which is moist but not as high as can be this time of year.
Expect a quiet Saturday night with areas of fog. Weather remains rain-free Sunday morning with fog/stratus burning off to sun. The pressure pattern looks weak, so expect sea breezes to develop along the eastern coast.
Showers/scattered thunder will initially develop north of Massachusetts during the midday/afternoon, with the northwest flow pushing the convection southeast. Best chance in Srn New England will be in Northern and Northeast MA, but convection may also develop in the low-level convergence along sea breeze boundaries near the coast. Winds 30-40 kt at 500-mb may add some strong wind gusts to the convection.
Dew points around 60 suggest Sat night min temps in the 60s. Guidance values for max temps were about 3F lower than observed values on Thursday, so this forecast will add 3F to guidance values for Sunday...85 to 90 inland and 80 to 85 in the coastal plain.
Monday through Thursday... Monday features a cold front moving through...the GFS moves it through early while the ECMWF waits til afternoon/evening. The airmass remains unstable with right entrance region of the upper jet over the region. The front stalls to our south, then sweeps north across Srn New England later Tuesday, which may generate some more convection. Another cold front approaches through Canada Wednesday and may stall over Northern New England Thursday. The airmass remains unstable through the period. PW values (Precipitable Water values) climb to 1.5 inches Monday, and then to near 2 inches Wednesday/Thursday.
Bottom line...expect a chance of showers/thunder each day. High PW values Wed/Thu suggest local downpours.
Mixing reaches to 850 mb or a little higher Monday, 925 mb Tuesday, and 850 mb Wed/Thursday. Temps aloft support mid to upper 80s Monday, low to mid 80s Tuesday, and lower 90s Wednesday/Thursday. Dew points are expected in the mid 60s early week, then upper 60s and around 70 Wed/Thursday. Heat index values will reach the mid 90s in some areas Wednesday and Thursday.
SCAs (Small Craft Advisories) remain in effect for most of the eastern waters through early this evening. Increasing northeast winds (gusts 25-30 kt) and building seas (3-6') associated with a backdoor front will lead to small craft advisory conditions on the eastern waters, though will get marginally close on southern waters later today into tonight. Areas of low clouds and fog tonight on most waters with periods of showers.
While still cloudy, easing winds and lowering seas should be the rule for Independence Day.
Outlook /Saturday Night through Tuesday/... Saturday Night: Winds less than 25 kt. Patchy fog. Visibility 1 to 3 nm.
Sunday: Winds less than 25 kt. Local visibility 1 to 3 nm.
Sunday Night through Monday: Winds less than 25 kt.
Monday Night: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms, patchy fog. Visibility 1 to 3 nm.
Tuesday: Winds less than 25 kt.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory until 11pm EDT this evening for ANZ250. Small Craft Advisory until 6pm EDT this evening for ANZ251. Small Craft Advisory from 1pm this afternoon to 11pm EDT this evening for ANZ254.