Boston Harbor Marine Forecast (2024)

Synopsis
Scattered strong to severe thunderstorms remain possible this evening...mainly across northern MA where a Severe Thunderstorm Watch is in effect. A backdoor cold front moves in from northeast to southwest Friday...bringing another round of showers and thunderstorms. The bulk of this activity should be across interior Massachusetts and Connecticut...where some of the storms may become severe and also result in a localized flash flood threat. Warm and muggy this weekend with rain and thunderstorm chances both Saturday and Sunday. A cold front sweeps across the region Monday with additional showers and storms, briefly less humid on Tuesday, but summer warmth and humidity returns for midweek.

Near Term - Until 6am Friday Morning
745pm Update

* Strong to Severe T-Storms through late evening in areas north of the CT/RI/MA State lines

* Localized damaging wind gusts & torrential rainfall which may result in a very localized flash flood threat

Shortwave energy across northern New England coupled with outflow and MLCapes still over 2000 J/KG has resulted in a solid line of strong to severe t-storms to enter northwest and northern MA early this evening. We think enough outflow will result in a risk for severe storms over the next 1-3 hours in areas at last north of the CT/RI/MA state lines. This is also supported by the latest machine learning probs from the CSU to the Nadocast and HRRR (High-Resolution Rapid Refresh) Neural network...which are all showing a quite robust signal for localized damaging wind gusts. Main question is how far south this convection will survive as it out-runs the greater forcing. Given that DCapes are still over 1000 J/KG...we expanded the Severe T-Storm Watch to the CT/MA border and extended it through 11 pm. Also...these storms will be capable of producing torrential rainfall and a localized flash flood threat.

Once this activity winds down later this evening...much of the overnight hours should feature dry/muggy weather. Overnight low temps will mainly be in the upper 60s to the lower 70s. We also may see some patchy ground fog develop overnight given light winds/high dewpoints especially where rain falls earlier in the evening.

Short Term - 6am Friday Morning Through Friday Night
Key Points... * Showers & t-storms anticipated Fripm with the severe weather threat/very localized flash flood threat across interior MA/CT

* Much cooler across eastern MA but still hot & humid towards the CT River Valley where Heat Advisories remain posted

Details... Friday... A backdoor cold front will be moving westward across the region Friday morning and into the afternoon. This will hold high temps in the 80s across much of eastern MA and temps along the immediate coast will probably fall into the 70s by afternoon. Further inland...high temps will top off in the upper 80s to the lower 90s with the warmest of those readings in the CT River Valley. The Heat Advisory for Friday will only cover portions of southwest MA/CT...where Heat Indices are expected to top off between 95 and 100 degrees.

The other concern will be for another round of showers & t- storms...which looks to be Friday afternoon/early evening. The focus for this will be along the backdoor cold front and will be enhanced by shortwave energy in west to northwest flow aloft. While a few showers & t-storms may impact the entire region...thinking the main focus for the potential of severe weather/localized flash flooding will be across western/central MA & northern CT. This is where the greater instability will reside on the order of 1500 to 2000 J/KG. These backdoor cold fronts can be a recipe for training and a localized flash flood threat. The CSU Machine learning probs highlight this risk nicely with again the focus across the interior. There also is a severe weather risk with the main concerns being locally damaging wind gusts with hail a secondary risk. This is depicted nicely by the machine learning probs as well as the HREF Updraft Helicity Swaths/Radar Simulations.

Friday night... The convection should dissipate Friday evening. Otherwise...we will have to watch for areas of low clouds and fog developing. Overnight low temps will be mainly in the 60s.

Long Term - Saturday Through Thursday

Highlights:

* Warm and muggy this weekend with rain chances both Saturday and Sunday.

* Cold front sweeps across the region on Monday, drier and returning heat into mid next week.

The mid-level ridge continues to deamplify, as 500mb heigheights lower from north to south, which is a consistent theme for the upcoming weekend. At the surface an area of higher pressure near Bermuda wanes and surface pressure lowers across the northeast. This area of low pressure developing over the northern Great Lakes, drives our weather conditions late this weekend into Monday, as the trailing cold front, south of the low, sweeps across the northeast sometime Monday. Beyond Monday, high pressure builds back Tuesday through Thursday, with a cold front possibly pushing across the region later on Friday/Saturday.

In addition, most of next week trends warmer than normal, and at this point, next week doesn't look to be as extreme as this current week. Though the ensemble situational awareness tables indicates Monday through Thursday, surface temperatures could be running between the 90th and 99th percentile (of climatology), with a return of average temperatures post cold front, sometime late Friday into Saturday.

Saturday & Sunday:

Getting closer to home, there is a quasi-stationary frontal boundary across the region, running from east to west through southern New England and through Upstate New York on Saturday. Weak area of low pressure tries to develop along the boundary, with the greatest area for showers and storms along and north of the Mass Pike during the mid to late afternoon. At this point, not expecting anything severe, and Storm Prediction Center has most of the region under general thunder. A slightly more elevated issue would be the potential for excessive rainfall. The ERO from WPC highligheights much of central/western Massachusetts and northern Connecticut for a 'Marginal' risk. Given PWATs (Precipitable Waters) are above two inches, isolated and locally heavy downpours could lead to urban street and poor drainage flooding.

Aforementioned frontal boundary becomes a warm front Saturday night into early Sunday, lifting northeast, and placing us in the warm sector. Scattered showers into the overnight hours, though the best forcing appears to be concentrated further north. A prefrontal trough and shortwave pivot through, with showers and thunderstorms later Sunday afternoon/evening.

As for temperatures, Saturday will be the 'cooler' day, the warmest location will be the Connecticut River Valley, highs here are in the mid 80s. Much cooler in northwest Massachusetts where highs are low to middle 70s with the northeast flow. Nightly lows are still mild which isn't ideal for sleeping with windows open, lows are in the middle to upper 60s to 70 degrees in the Connecticut River Valley on Saturday night, then 2-4 degrees warmer Sunday night.

Next Week:

Warm and muggy day ahead of a surface cold front with temperatures climbing into the 80s and dew points in the 60s. Storms develop mid to late afternoon with the surface cold front, a bit a relief behind the front with lowering dew points into the 50s and leads to a nice Tuesday with comfortable, albeit warm day, with dew points in the upper 50s to 60F. High pressure reestablishes across the northeast leading to a drier week with return of summer warmth. Highs are in the middle and upper 80s and lows in the 60s with a sign of cooler temperatures by late in the week.

Marine
Forecaster Confidence Levels:

Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.

Tonight through Friday night...High Confidence.

Nearshore small craft wind gusts will linger from areas near the southeast New England coast into early this evening...so small craft headlines continue in this region through 8 pm. Other risk tonight will be a few strong t-storms which may threaten our northern waters through about 10 pm. We also will need to watch for some fog developing overnight.

The backdoor cold front will move across our northern waters Fri morning...but likely stall across our southern waters Fri afternoon and night. Pressure gradient will be weak enough to keep winds/seas below small craft thresholds. We will need to watch for areas of fog developing during the overnight hours.

Outlook /Saturday through Tuesday/... Saturday: Winds less than 25 kt. Chance of rain showers, patchy fog, isolated thunderstorms. Visibility 1 to 3 nm.

Saturday Night: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Rain showers likely, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain showers likely, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Monday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Climate
All Time June High Temperature Record (Daily)

BOS - 100 F (06/06/1925, 06/26/1952 and 06/30/2021) BDL - 100 F (06/26/1952, 06/30/1964) PVD - 98 F (06/25/1943, 06/15/1945 and 06/30/1945) ORH - 98 F (06/26/1952)

Most recent day of 100 F (or greater)

BOS - 100 F (07/24/2022) BDL - 100 F (07/21/2019) PVD - 100 F (07/28/2020) ORH - 102 F (07/04/1911)*

* For ORH this is the only 100+ degree day in its period of record.

Daily High Temperature Records... June 20th

BOS - 98 F (1953) BDL - 97 F (2012) PVD - 95 F (1941) ORH - 93 F (1953)

June 21st

BOS - 96 F (2012) BDL - 96 F (1953 and 2012) PVD - 96 F (1941) ORH - 91 F (Multi-Years)

Daily Warmest Low Temperatures Records... June 20th

BOS - 78 F (1931) BDL - 74 F (1931) PVD - 74 F (1931) ORH - 72 F (1931)

June 21st

BOS - 80 F (2012) BDL - 73 F (1923 and 2012) PVD - 75 F (2012) ORH - 74 F (1923 and 2012)

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...
Heat Advisory until 7pm EDT Friday for CTZ002>004.
Air Quality Alert until 11pm EDT this evening for CTZ002-003. MA...
Heat Advisory until 7pm EDT Friday for MAZ008>011.
Air Quality Alert until 11pm EDT this evening for MAZ007- 010>021. RI...
Air Quality Alert until 11pm EDT this evening for RIZ001>005.

Marine
Small Craft Advisory until 8pm EDT this evening for ANZ231>234-254-255.