Nantucket Sound Marine Forecast
|Overnight...Se Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Thu...E Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Afternoon. Seas 2 To 3 Ft. A Chance Of Rain.|
|Thu Night...E Winds 15 To 20 Kt, Increasing To 20 To 25 Kt After Midnight. Gusts Up To 30 Kt. Seas 3 To 5 Ft. Rain. Vsby 1 Nm Or Less.|
|Fri...Se Winds Around 20 Kt, Becoming Sw In The Afternoon. Gusts Up To 30 Kt. Seas 4 To 6 Ft. Rain Likely. Vsby 1 Nm Or Less.|
|Fri Night...W Winds 15 To 20 Kt With Gusts Up To 30 Kt. Seas 4 To 6 Ft. Showers Likely.|
|Sat...Nw Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt In The Afternoon. Gusts Up To 25 Kt. Seas 3 To 5 Ft. A Chance Of Showers.|
|Sat Night...Nw Winds 5 To 10 Kt. Gusts Up To 20 Kt In The Evening. Seas 2 To 3 Ft.|
|Sun...W Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Sun Night And Mon...Sw Winds 5 To 10 Kt. Seas Around 2 Ft. Patchy Fog.|
|Mon 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
1014pm EDT Wednesday April 14 2021
Approaching low pressure will result in showers developing overnight across western Massachusetts and western Connecticut, gradually overspreading the region from west to east during Thursday. Widespread rain, heavy at times, is expected Thursday night into Friday with rain changing to accumulating snow in the Berkshires and portions of the Worcester Hills. Gradual improvement is expected over the weekend as the storm exits out to sea, with dry milder weather likely Sunday. Rain may return early to mid week.
Near Term - Through Thursday
Rain continues to remain suppressed well to our southwest this evening across New Jersey and Pennsylvania. Given that precipitation is stubborn to approach, POPs were dropped across our western zones to slow the progression of showers before sunrise. Our previous forecast suggested that showers would overspread Western Zones around 09z, however much of the guidance suggests that the bulk of precipitation will move in after 12Z. Precipitation will be slow to progress into our area overnight before blossoming across W. CT and MA just after sunrise.
Otherwise, the forecast is in good shape. High clouds have reached as far east as Boston and will limit radiational cooling. Temperatures will fall an additional 3-5 degrees across most areas before sunrise from their current values.
Tonight... Anomalous upper low will move slowly south from the upper Gt Lakes region tonight as ridge axis slides to the east resulting in upper flow gradually backing. This will bring deeper moisture plume northward into western New Eng tonight with showers increasing in coverage through the night as large scale forcing increases ahead of the trough. The showers will be confined to western New Eng with eastern MA and RI remaining dry. Lows will range from mid/upper 30s across SE New Eng where a period of radiational cooling expected this evening before clouds increase, to low/mid 40s in the CT valley.
Thursday... Large scale forcing for ascent will continue to increase from west to east as the upper low approaches from the west and surface low develops off the mid Atlantic coast. Widespread rainfall is expected in western New Eng but it will be a slow process moving eastward with ridging hanging on east of New Eng. Light rain will reach eastern MA later in the afternoon. Highs will reach lower 50s in eastern MA where it will be mostly dry into early afternoon, with highs in the 40s in western New Eng but cooling in the afternoon.
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/... Thursday night into Friday... * Significant elevation snow expected in the Berkshires and to a lesser extent over the Worcester Hills
Anomalous upper low will be approaching New Eng from the west Thu night, moving into the region during Fri. This will be a quite a dynamic system with the dynamic tropopause lowering to around 600 mb as the upper low approaches. Strong forcing for ascent combined with steepening mid level lapse rates and deep moisture plume will bring widespread precip, heavy at times across SNE. Also, can't rule out an isolated t-storm.
Cooling from top down as heigheights fall and dynamic cooling from strong omega will result in rain flipping to snow in the Berkshires by Thu evening and gradually over the Worcester Hills and northern CT hills later Thu night. Rain should even mix with or briefly change to snow in the CT valley and lower elevations in central MA overnight as colder air deepens west of the low which tracks across SE New Eng. However, expect all rain in RI and eastern MA.
The heaviest accums will be in the Berkshires where the column is coldest the longest during the heavy Quantitative Precipitation Forecast and the fact that the heaviest Quantitative Precipitation Forecast will be falling at night will be helpful to snow accumulations. The heaviest precipitation will linger into Fri morning in the interior before lifting out. The period of best accum will likely occur through about 9-10am Fri over the higher elevations then warming boundary layer and lighter precipitation rates will limit accumulations. Also, there is a dry slot to contend with that will be lifting northward by Fri morning along the coast then spreading north across eastern half New Eng.
We used a blend of available guidance for Quantitative Precipitation Forecast and a SLR of 7-9:1 over high terrain to derive snow accum. Expect accums of 4-8 inches in the Berkshires with localized higher amounts possible at elevations above 1500 ft. In the northern Worcester hills, potential for 3-6 inches over the highest elevations with an inch or 2 over the hills in northern CT. The main concern is potential for power outages due to the weight of the heavy wet snow on trees and power lines. There will be impact to travel over the higher elevations with snow covered roads, but limited impact at lower elevations with just wet or slushy roads.
Regarding Quantitative Precipitation Forecast, widespread 1-2 inches of liquid equivalent precipitation expected with locally higher amounts in the west. Amounts may remain below an inch across the Cape/Islands.
It will become windy late Thu night into Friday from Cape/Islands northward along the eastern MA coast as the low level jet lifts northward. Gusts to 30-40 mph are possible.
Long Term - Friday Night Through Wednesday
Highlights... * Lingering showers Friday night into early Saturday then drying trend for latter half of Saturday but remaining chilly. * Warming trend begins on Sunday and continues into first part of the work week. A few showers are possible Sunday and Monday with Tuesday looking to be the pick of the week. * Pattern could become unsettled again mid week but confidence is low at this time.
Friday night into Saturday... We remain in a negative NAO pattern which means high latitude blocking. This means that the upper low will be slower to exit into the Canadian maritimes, which increases the likelihood of unsettled weather continuing through Friday night and into first part of the weekend. While the mid levels dry out, low levels remain saturated. Overall, Saturday looks chilly with the possibility of lingering rain showers (light snow showers possible in the high terrain). However, the latter half of Saturday should feature a drying trend with the return of partial sunshine.
Sunday into Monday... Sunday should be the better day of the weekend, as westerly flow brings about a warming trend with seasonable high temperature of mid 50s to around 60. Couldn't rule out a few showers later on Sunday as a disorganized shortwave slides to our south. Better chances for unsettled weather on Monday with better probability of a few more showers around. Many areas should stay dry, however, so expect highs in the upper 50s to mid 60s.
Tuesday into Wednesday... Warming trend continues into the first half of the work week as flow becomes west and eventually southwest prior to our next mid level trough mid week. 850 mb temps gradually rise to around +2 to +4C and with mixing up to that level, mid to upper 60s should be widespread away from the immediate coast on Tuesday. Tuesday also looks dry so it could turn out to be pick of the week. Beyond Tuesday, forecast confidence really drops off because it depends on how the upper flow pattern evolves. A cold front looks to cross our area sometime on Wednesday bringing the chance for scattered showers. Confidence is low on the rainfall amounts and high temperatures, which hinge what time the frontal passage occurs.
East winds will be ramping up Thu afternoon with gusts to 25-30 kt developing over the southern waters. The peak of the wind will occur late Thu night into Fri from south to north as the low level jet lifts north over the waters. Gusts to 35-40 kt expected, especially over eastern MA waters where gale watches will continue.
Outlook /Friday Night through Monday/... Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 12 ft. Chance of rain showers, patchy fog.
Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain showers.
Saturday Night: Winds less than 25 kt. Local rough seas.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, patchy fog.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.
Tides / Coastal Flooding
A storm surge of 1.5 to 2 ft is possible late Thu night into Fri as the peak of the easterly winds develop. Fortunately, rather low astronomical tides will preclude any coastal flooding for the eastern MA coastline. The worst case scenario is for minor splashover for the most vulnerable shore roads along Nantucket Harbor during the overnight high tide late Thu night.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...Winter Storm Watch from Thursday evening through Friday evening for MAZ002-008-009. RI...None.
Small Craft Advisory from 2pm Thursday to 8pm EDT Friday for ANZ232>235-237-256. Gale Watch from late Thursday night through Friday afternoon for ANZ231-250-251-254. Small Craft Advisory until 5am EDT Friday for ANZ250-254. Small Craft Advisory until 8pm EDT Friday for ANZ255.