Cape Cod Bay Marine Forecast
|Today...N Winds 5 To 10 Kt. Seas 1 Foot Or Less, Then Around 2 Ft This Afternoon. A Chance Of Showers With Isolated Tstms. Patchy Fog This Morning. Some Tstms May Produce Gusty Winds And Heavy Rainfall. Vsby 1 To 3 Nm This Morning.|
|Tonight...N Winds 10 To 15 Kt. Gusts Up To 20 Kt After Midnight. Seas Around 3 Ft. Patchy Fog. Vsby 1 To 3 Nm, Decreasing To 1 Nm Or Less After Midnight.|
|Wed...N Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Morning. Seas Around 3 Ft.|
|Wed Night...Ne Winds 5 To 10 Kt. Seas 2 To 3 Ft.|
|Thu...Ne Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Thu Night...S Winds 5 To 10 Kt. Seas Around 2 Ft In The Evening, Then 1 Foot Or Less.|
|Fri...S Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Fri Night...Sw Winds 5 To 10 Kt. Seas Around 2 Ft. A Chance Of Showers In The Evening.|
|Sat...Sw Winds 5 To 10 Kt. Seas 1 Foot Or Less.|
|Sat Night...Sw Winds 5 To 10 Kt. Seas 1 Foot Or Less. Winds And Seas Higher In And Near Tstms. 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
656am EDT Tuesday July 14 2020
Strong to severe thunderstorms possible across portions of southern New England this afternoon. Main threats are damaging wind gusts, hail and heavy rainfall which could bring localized flash flooding. Will be cooler in comparison to the past several days, but the humidity remains. High pressure then brings fair weather for Wednesday and Thursday. Scattered showers and thunderstorms return early Friday and Friday night. High pressure then bring rain-free but very warm weather for Saturday and Sunday. Another cold front may bring a few thunderstorms Monday.
.NEAR TERM Through Tonight
7 am update..
While further north in NH severe storms were ongoing early, in southern New England, further from the closed upper low, showers have struggled to get going. This is to be expected given lack of a strong forcing mechanism before diurnal heating gets going. Mesoanalysis indicated a good deal of convective inhibition across the region. Model soundings indicate the cap should erode around 15-16Z which is when that instability will begin to be realized and storms become more formidable.
Previous Discussion... * Isolated strong to severe thunderstorms possible across southern New England today. Main threats from storms are damaging wind gusts and heavy rainfall, which could produce localized flash flooding. In addition, hail cannot be ruled out.
* Cooler temperatures in comparison to the past couple of days.
A negatively tilted trough digs into northern New England today. The surface low associated with the trough will remain offshore into the Gulf of Maine.
Expect the surface low to reinforce cool, stable onshore flow across eastern MA and RI. The interior will see north to northeast winds throughout the day. How strong this onshore flow is bring some questions in regards to the thunderstorm activity today. However, further from the coast there is a better opportunity for showers and storms.
Aloft the 500 hPa trough will dig into northern New England. This will bring an anomalously cold air mass into the region aloft with 500 hPa temperatures between -10 to -15 degrees Celsius. This cold pool(a region of relatively cold air) moving in aloft in combination with the trough overhead and diurnal heating will result in scattered shower and thunderstorm development. Dew points not expected to drop much despite the northerly to northeasterly flow with readings generally in the mid to upper 60s. So, there is plenty of moisture available.
Stability values across New England range generally from 1000-1500 J/kg of MUCAPE. Though the ARW/NMM does feature values increasing to 2000-2500 J/kg. Bulk shear values are around 20 to 30 kts within the 0-6 km layer. So not completely ideal wind shear aloft, but this can be compensated for by the higher instability. Low level lapse rates are expected to increase to 7 to 8 degrees Celsius per km. Mid level lapse rates are supportive to maintain updrafts. Models keep values around 6 to 7 degrees Celsius per km. Do have a few hundred J/kg of DCAPE and there is a decent amount of CAPE within the hail growth zone. Forcing is a bit weaker today in comparison to yesterday, so that is also a question. Think the best chance for strong to severe storms will be across central MA into the Merrimack Valley. This is also supported by some 2-5 km updraft helicity swaths per the HREF and SREF Craven Brooks SIG Severe Index values greater than or equal to 10k. This is also indicated per the Storm Prediction Center Day 1 Outlook.
Along with the threat of strong to severe storms there will be the threat of heavy rainfall. Will see PWAT (Precipitable Water) values between 1.25 to 1.5 inches, which is approaching the 75th percentile per SPC Sounding Climo for CHH. The HREF neighborhood probability matched mean guidance does indicate that there is a 50 to 70 percent chance of 3-hr Quantitative Precipitation Forecast values greater than 1 in, but no probabilities of 3-hr Quantitative Precipitation Forecast values greater than 3 in as was the case yesterday. This again highlighting the greatest risk across central MA into the Merrimack Valley this afternoon. Do have some concerns for northeast MA given that storms moved through today, so will need to closely monitor.
Will be cooler today in comparison to the past couple of days. Flow at 850 and 925 hPa will be generally out of the northwest to north. This will advect cooler air in. Highs range from the mid 70s to the low 80s, though there may be come mid 80 degree readings across the CT River Valley.
Short Term - Wednesday
* Any showers and storms diminishing during the evening. Low clouds linger tonight due to onshore flow. Much cooler with lows falling into the 50s across the interior and the low 60s along the coast.
* Drier weather across southern New England on Wednesday. Cannot rule out an isolated shower across the CT River Valley. Cooler temperatures continue with readings generally in the 70s.
Tonight... Nearly neutrally tilted trough slides offshore. Behind the trough a ridge axis will build from the central Great Lakes into the eastern Great Lakes.
Shower and storms diminishing as the trough lifts offshore and due to the loss of heating. Onshore flow persists and expect low clouds to advect further inland. Dew points falling into the upper 50s and low 60s across the region. Will feels much more comfortable. Low temperatures falling into the 50s across the interior and the low 60s along the coast.
Wednesday... Ridge axis building into western portions of New England from the eastern Great Lakes. This will provide dry and quiet weather across the majority of southern New England. Will have cool northeasterly winds becoming easterly at 925 hPa. This will continue to advect cooler air in. Dew points remain comfortable with readings in the upper 50s and low 60s. High temperatures generally in the 70s. Could have some low 80s across the CT River Valley.
Not out of the question that the combination of the easterly flow and diurnal heating results in some orographically driven showers across the higher terrain of CT and western MA. Little to no instability present, so do not anticipate any thunderstorms.
Long Term - Wednesday Night Through Monday
Highlights... * Mostly dry Thursday then rain and thunderstorms return late Thursday night and Friday
* Warmer temperatures and increasing humidity for the weekend
Details... High pressure remains in control at the surface with mid level ridging aloft Wednesday night and Thursday. The pattern breaks down late Thursday night and Friday as a mid level shortwave and frontal system swings through bringing the return of rain and thunderstorms. Zonal flow and high pressure influence keep dry and increasingly hot/humid conditions in the forecast for the weekend into next week.
High pressure nosing down from Quebec remains in place Wednesday night into Thursday. This keeps southern New England largely dry with partly cloudy skies as moisture lingers around 850 mb. Temperature-wise things remain relatively comfortable and below normal; in the low 80s inland, mid-upper 70s east. This will be the last day of the cooling NE flow influence, however, as winds shift out of the SE late in the day and SW by Thursday night as the high moves out.
On its heels is a surface low over southern Canada moving into northern New England Thursday night and Friday. Timing has been slowed down a bit, but by early Friday morning warm air advection showers should have moved into western MA ahead of the cold front which moves through around late Friday night or early Saturday morning. Ahead of the cold front convective parameters are marginally favorable for a few strong storms (CAPE near 1000 J/kg and bulk shear of 25-30 kts) but lapse rates are rather poor which could be a limiting factor. Thunderstorm potential will likely be dependent on the timing of the cold front which, if it comes through as slowly as it's looking currently, may be too late to take advantage of the more favorable afternoon temperature profile. Stay tuned.
For the weekend the post frontal airmass looks drier with high pressure building over southern New England. This brings with it the return of normal to above normal temperatures nearing 90 F. The airmass becomes less comfortable too, as higher humidity returns on southerly flow; dewpoints once again approaching 70 F.
Small Craft Advisories remain in effect across the southern waters due to wave heigheights around 5 ft. Low clouds and fog across the eastern waters into late this morning. May need a Small Craft Advisory late tonight across the eastern waters due to building waves. This is a result of strengthening northeast winds. Have held off in the current update as have some doubts in wind speeds and resultant waves.
High Surf Advisory remains in effect for the Islands, including Block Island, until Tuesday evening for south facing beaches due to the rip current risk and breaking 4-6 ft waves in the surf zone.
Outlook /Wednesday Night through Saturday/... Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft.
Thursday: Winds less than 25 kt.
Thursday Night: Winds less than 25 kt. Slight chance of rain showers.
Friday through Friday Night: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.
Saturday: Winds less than 25 kt.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...High Surf Advisory until 8pm EDT this evening for MAZ023-024. RI...High Surf Advisory until 8pm EDT this evening for RIZ008.
Small Craft Advisory until 8pm EDT this evening for ANZ235- 237-255-256.