Boston Harbor Marine Forecast
|Overnight...Se Winds 10 To 15 Kt With Gusts Up To 25 Kt. Waves Around 2 Ft. A Chance Of Showers.|
|Mon...Se Winds 10 To 15 Kt With Gusts Up To 25 Kt, Becoming S 15 To 20 Kt With Gusts Up To 35 Kt In The Afternoon. Waves 2 To 3 Ft. Patchy Fog. Showers.|
|Mon Night...W Winds 15 To 20 Kt With Gusts Up To 35 Kt. Waves Around 2 Ft, Except 3 To 5 Ft At The Outer Harbor Entrance. Showers Likely.|
|Tue...W Winds 15 To 20 Kt With Gusts Up To 25 Kt, Diminishing To 10 To 15 Kt In The Afternoon. Waves Around 2 Ft.|
|Tue Night...Nw Winds 5 To 10 Kt. Waves 1 Foot Or Less.|
|Wed And Wed Night...N Winds 10 To 15 Kt With Gusts Up To 20 Kt. Waves Around 2 Ft. A Chance Of Snow And Rain.|
|Thu...N Winds 10 To 15 Kt With Gusts Up To 20 Kt. Waves Around 2 Ft, Except 3 To 5 Ft At The Outer Harbor Entrance. A Chance Of Snow.|
|Thu Night And Fri...Se Winds 5 To 10 Kt. Waves 1 Foot Or Less, Then Around 2 Ft. At The Outer Harbor Entrance, Waves 2 To 4 Ft. A Chance Of Rain And Snow.|
|Fri Night...S Winds 5 To 10 Kt. Waves 1 Foot Or Less, Except 2 To 4 Ft At The Outer Harbor Entrance. A Chance Of Rain. 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
1052pm EST Sunday Dec 5 2021
High pressure moves offshore tonight. A warm front lifts north across southern New England Monday morning with a period of showers and isolated thunderstorms possible along with unseasonably mild conditions. A strong cold front sweeps across the region Monday evening which will be accompanied by another period of showers and strong winds Monday afternoon and evening. Dry and cooler than seasonable air works into the region late Monday night and Tuesday. A coastal storm may bring some accumulating snowfall across southern New England Wednesday into Wednesday night, but there is considerable uncertainty. Dry weather returns on Thursday before we become more unsettled late in the week and heading into the weekend with warmer temperatures.
Near Term - Until 6am Monday Morning
Minor tweaks to the forecast this evening. Tried to update precipitation timing. Thought there was good agreement amongst theNear Term - Rest Of Today Through Tonight
ance, especially the HRRR, RAP and 3 km NAM. Used a consensus approach as the basis for changes. Still looking complicated for early Monday morning. Lots of helicity is still projected, but not much instability to tap into it. Will need to monitor any convection early Monday morning. If it gets strong enough, it could develop some rotation.
Brought temperatures and dew points in line with observed trends. Still thinking there is a really low risk for some light icing along and north of Route 2 late tonight. Based on latest guidance, this window should only last for 1-2 hours. Still do not have enough confidence for any headlines at this time. It may be a last minute thing. Yet another aspect of the forecast to monitor closely overnight.
No changes in the latest update other than making minor adjustments to cloud cover to move more in line with current obs. Rest of forecast is unchanged.
Previous discussion... High pressure moves offshore tonight as potent mid level trough and shortwave moves across the Gt Lakes. A lead shortwave within the SW flow aloft and attendant surface low lifts north along the mid Atlantic coast overnight. CAMs all show convective showers developing over the ocean overnight within an area of marginal elevated instability. These showers will move up along the south coast into portions of CT, RI and SE MA toward daybreak. Meanwhile, some spotty light precipitation may develop late tonight across western MA. Temps tonight will drop to near freezing or a bit below in the interior before slowly rising late tonight. If precipitation develops early enough, there is a low risk for isolated light freezing rain across portions interior northern MA along route 2 corridor to the east slopes of the Berkshires. However, this risk is quite low and areal coverage would be very limited. The more likely scenario is that temps will be a bit above freezing when precipitation moves in. Will have to closely monitor this overnight. Otherwise, temps will be rising through the 40s near the coast as SE winds increase.
Short Term - 6am Monday Morning Through Monday Night
Monday... Convective showers lift north across SNE during the morning as warm front moves northward. There is marginal elevated instability with HREF indicating MUCAPE of 200-500 J/kg across eastern New England so can't rule out an isolated t-storm across eastern CT, RI and eastern MA during the morning. While, low level shear values are impressive soundings show a rather pronounced low level inversion in the morning which would preclude any stronger convective winds from mixing down to the ground.
Warm sector airmass overspreads SNE in the afternoon with temps soaring into the mid 50s higher terrain to lower 60s coastal plain. Expect a period of dry conditions late morning into the afternoon before deeper moisture moves in from the west as strong cold front approaches. A band of showers expected to move into western MA/CT late in the day.
Strong winds are other concern for Monday afternoon and evening as 60+ kt low level jet develops across SE New Eng. Given SW flow, mixing will be deeper than what we normally see with a S or SE wind. Forecast soundings show potential for a period of 40-50 mph gusts across SE New England late Monday into Monday evening. As a result we issued a wind advisory for Cape/Islands into SE coastal MA and Newport county in RI. Elsewhere, gusts 30-40 mph are possible.
Monday night... Cold front moves across SNE during the evening and will be accompanied by a period of widespread showers which move off the coast just after midnight. Turning colder with partial clearing developing overnight with lows upper 20s to mid 30s. The rain may end as a brief period of snow over the higher terrain.
Strong pre-frontal SW winds in the evening, gusts 25-40 mph except 40-50 mph SE New England coast where wind advisory continues. Post- frontal W winds will be less but it will still be blustery overnight.
Long Term - Tuesday Through Sunday
Highlights... * Drier with near to cooler than seasonable temperatures on Tuesday.
* Potential for accumulating snowfall late Wednesday into Wednesday night. However, it is still too early to hone in on specific amounts and the exact details as there is considerable uncertainty in the track/intensity of the low passing by. Travelers will want to stay tuned to future updates.
* Drier on Thursday as a weak high builds in. Unsettled late in the week and heading into the weekend. May start off as snow before it transitions to rain. Seasonable readings on Thursday before we trend warmer than normal on Saturday.
Tuesday and Tuesday night... Cyclonic flow in place across much of the US. Fairly weak mid level ridge builds from the eastern Great Lakes/Quebec into northern New England/eastern Canada. A trough digs into the Mid/Upper Mississippi River Valley late on Tuesday. A the surface weak high builds into the region from Quebec/eastern Great Lakes. The high shifts into eastern Canada by late Tuesday night.
Dry and quiet weather anticipated across southern New England. Will start off a bit blustery due to a tightened pressure gradient, but will relax as the high gradually builds in. Did bump up high temps slightly due to W/WNW flow aloft at 925 hPa resulting in some downsloping. Went with the 75th percentile of guidance, which is roughly seasonable readings for this time of year, but will be much cooler in comparison to Monday. Highs in the mid/upper 30s across the higher terrain and the low/mid 40s elsewhere.
Will see increasing mid/high cloud cover late on Tuesday and especially Tuesday night ahead of the next incoming system. Should remain dry with high pressure still in control, so dialed back the default NBM precipitation chances based on the latest guidance. Think that we will remain dry until a bit later in the day Wednesday. Given the cloud cover will be tough for temps to really plummet, but given the highs position could have some cold air drainage due to a northerly ageostrophic wind component. Low temps in the 20s for most except along the immediate coastline where readings are around 30.
Wednesday into early Thursday... Lots of uncertainty during this timeframe there is potential for widespread accumulating snowfall, but really too early to tell given the spread amongst guidance. A positively tilted trough will be situated over the Mid/Upper Mississippi River Valley will dig into the central Great Lakes/Ohio Valley and become neutrally tilted during the afternoon. The trough then lifts into the Mid Atlantic becoming negatively tilted by the evening and through New England by early Thursday. At the surface, low pressure will develop offshore from the VA/NC coast and lift northeastward south of southern New England late on Wednesday. The low lifts offshore to the east/southeast of southern New England by late Wednesday/early Thursday.
Still have considerable uncertainty in this timeframe with respect to Quantitative Precipitation Forecast/snowfall amounts and anticipated impacts. The reason for the uncertainty is due to both the intensity and track of the surface low. Lots of spread amongst guidance with the current trend being the system being weaker and staying further offshore to the S/SE. No point in getting into the specific details at this point as we still need to really hone in on the track of the surface low to determine the impacts. The GFS right now features more of a snow lovers track passing just to the SE of the benchmark, whereas the ECMWF/GEM/NAM give us not much of anything. Within this window have honed in more on the EPS/GEFS ensemble guidance, which also have been showing trend of the low staying further offshore at this point in time. There are 5/30 GEFS members indicating there could be warning level snowfall accumulation assuming a 10-1 SLR. Whereas 14/30 show not much if any snowfall accumulation. The EPS features no members showing warning level accumulations with the 10-1 SLR and the vast majority showing not much if any accumulations. Both EPS/GEFS members have been trending in the wrong direction for snow lovers with probabilities of amounts AOA 1 or 3 inches. Given the uncertainty have stuck with the NBM guidance at this point in time and nudged down WPC precipitation slightly. Given we are still talking 4- 4.5 days out will need to see if this trend continues and get better consensus amongst guidance. If folks have travel plans they will want to stay tuned to future updates. Appears at this time given the progressive nature of the system that if there were impacts to travel it would be more for the late afternoon/evening commute. Given the progressive nature of the system precipitation should be over with before daybreak.
High temperatures on Wednesday will be cooler than seasonable with readings generally in the 30s, but the Cape/Islands could see readings in the low 40s. Low temperatures heading into Thursday morning would be fairly widespread 20s with low 30s across the Cape/Islands.
Thursday... Weak high builds over southern New England in wake of the exiting system. Will have cool NW/N flow aloft, which advects colder air into the region. High temps will be below normal for this time of year with fairly widespread 30 degree readings.
Some uncertainty with respect to the temps heading into Friday morning. Models spread out on how strong a warm air advection we get ahead of the next trough lifting in. Have stuck with NBM, but not out of the question we are too cold at the moment give some models 925 hPa temps. Right now lows in the 20s across the interior and low 30s for the Cape/Islands.
Friday and Saturday... Given the uncertainty earlier in the forecast, have not put much emphasis this far out. Does appear that we have shortwaves/troughs lifting into the region. This could bring us some light snow/flurries heading into Friday. Does appear at the moment that based on temp profiles would see precipitation change over to rain for Friday and also for Saturday. Should be much warmer than normal during this timeframe with pretty good consensus in a warm up. High temps on Friday in the 40s with some low 50s along the south coast. For Saturday, right now have widespread highs in the 50s.
Forecaster Confidence Levels.
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Increasing SE winds later tonight then a period of SW gusts to 35- 40+ kt developing in the afternoon/evening as 60 kt low level jet develops. Gale warnings continue on all waters. Winds shift to W Monday night behind the cold front with gusts gradually diminishing to 25- 35 kt. Scattered showers with an isolated t-storm possible late tonight and Monday morning, then another period of showers Monday night, clearing late.
Outlook /Tuesday through Friday/... Tuesday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas.
Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.
Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain likely.
Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain likely, chance of snow.
Thursday: Winds less than 25 kt. Rough seas up to 10 ft. Slight chance of rain, slight chance of snow.
Thursday Night: Winds less than 25 kt. Areas of rough seas. Slight chance of rain, slight chance of snow.
Friday: Winds less than 25 kt. Areas of rough seas. Chance of rain.
Tides / Coastal Flooding
The following are the astronomical heigheights of upcoming high tides and do not include surge values from local wind/weather conditions.
Boston 12.0 feet - 1214pm Monday
Nantucket 4.4 feet - 120pm Monday
Providence 5.8 feet - 917am Monday
Given southerly winds, not expecting much surge on the east coast with tidal anomalies less than 0.5 ft. Worst case along the east coast is minor splash over for most vulnerable shoreline roads.
Along the south coast, a surge of 0.5-1 ft is possible but this will likely occur after the high tide so not expecting any impact on the south coast for the Monday morning high tide.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...Wind Advisory from 1pm Monday to 1am EST Tuesday for MAZ019>024. RI...Wind Advisory from 1pm Monday to 1am EST Tuesday for RIZ007- 008.
Gale Warning from 10am Monday to 7am EST Tuesday for ANZ231>235-237-250-251-254>256. Gale Warning from 10am Monday to 1am EST Tuesday for ANZ230- 236.