Boston Harbor Marine Forecast
|Rest Of Tonight...Se Winds 5 To 10 Kt. Waves 1 Foot Or Less. Patchy Fog. Rain.|
|Sun...E Winds 10 To 15 Kt, Increasing To 15 To 20 Kt In The Afternoon. Gusts Up To 25 Kt. Waves 2 To 3 Ft. Patchy Fog. Rain. Vsby 1 To 3 Nm.|
|Sun Night...Ne Winds 15 To 20 Kt With Gusts Up To 25 Kt. Waves 2 To 3 Ft, Except 4 To 6 Ft At The Outer Harbor Entrance. Patchy Fog. Rain. Vsby 1 Nm Or Less.|
|Mon...Ne Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Afternoon. Waves 2 To 3 Ft. Patchy Fog. Scattered Showers. Vsby 1 Nm Or Less.|
|Mon Night...Ne Winds 10 To 15 Kt With Gusts Up To 20 Kt. Waves 2 To 3 Ft, Except 4 To 6 Ft At The Outer Harbor Entrance. Patchy Fog. Scattered Showers. Vsby 1 To 3 Nm.|
|Tue...Ne Winds 10 To 15 Kt With Gusts Up To 20 Kt. Waves 2 To 3 Ft, Except 4 To 7 Ft At The Outer Harbor Entrance. Patchy Fog. Scattered Showers.|
|Tue Night...Ne Winds 5 To 10 Kt. Waves 2 To 3 Ft.|
|Wed...Ne Winds 5 To 10 Kt. Waves 2 To 3 Ft.|
|Wed Night Through Thu Night...Nw Winds 5 To 10 Kt With Gusts Up To 20 Kt. Waves 2 To 3 Ft. A Chance Of Showers. 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
216am EDT Sunday Mar 29 2020
Rain will continue tonight into early Monday morning as a secondary low pressure develops just to our south. Weather pattern remains unsettled and cloudy for much of the upcoming week, with seasonably cooler temperatures. Intervals of scattered rain and/or snow showers Monday into Tuesday, with light snow coatings possible in the higher terrain. Still monitoring a potential coastal low Wednesday into part of Friday whose impact to Southern New England will depend on storm track. Periods of rain/wet snow would be possible, with little if any impact if the storm tracks further offshore.
Near Term - Until 6am This Morning
No changes in the latest update.
Increased precipitation chances along with wind speeds and gusts per observations. Rest of the forecast remains on track.
Radar and observations indicate initial warm-frontal rains have overspread a good chunk of Southern New England, roughly southwest of a Fitchburg to Norwood to Marshfield line as of this update. Prior to the rain arriving, it had been so dry (T-TD spreads some 20-30 degrees in most places) that the initial onset of rain has caused temperatures to fall very quickly and dewpoints/relative humidities to rise. North of that described line, temperatures away from the northeast coasts were in the low to mid 50s, but have fallen from highs in the 50s into the 40s in areas that have seen rain. Spotters and social media reports from Belchertown and Chester have even reported some sleet/pellets at times despite air temps that are well above freezing.
Used a blend of the HRRR (High-Resolution Rapid Refresh) and the HREF to re-shape Probability of Precipitation thru midnight, generally spreading categorical-PoP rains in a couple hours sooner. Also tried to show temperatures cooling pretty quickly and dewpoints rising as rain overspreads. Lows still look on track, however.
Previous discussion follows... Looking at a fairly common spring-time pattern developing tonight. Expecting a cutoff mid level low to move from the Northern Plains into the Great Lakes overnight. At the surface, high pressure moves farther offshore, resulting in an onshore flow. In between these two features, at least some weak lift is favored. This should lead to a widespread rainfall, eventually. Abundant low level dry air will need to be overcome before any rainfall reaches the ground. Had some reports earlier this afternoon of some ice pellets, due to evaporational cooling. With surface dewpoint depressions still about 20-30 degrees, it will be a while longer before appreciable rainfall reaches the ground.
As for timing, it will really depend upon where one is located. The western half of southern New England should see rainfall developing between now and 7 PM, with the eastern half of southern New England seeing the rain develop between 7pm and midnight Sunday.
Above normal low temperatures expected with the clouds already In place, and only getting lower and thicker.
Short Term - 6am This Morning Through 6pm Monday
Cutoff low should move from the Great Lakes to New England during this time. Most of the 28/12Z guidance suggests a secondary surface low pressure develops just to our south, then lingers Sunday night into Monday. While this should mean plenty of ascent to generate rainfall, the amount of available moisture is not so certain. Precipitable water values start out 3-4 standard deviations above normal Sunday, then drop off to near normal Sunday night. Expectation is for widespread rain to become more showery in nature, with perhaps a persistent drizzle developing beneath the drier air aloft.
Low risk for an elevated thunderstorm towards the south coast of New England Sunday afternoon into Sunday night with the development of the secondary low pressure. Lapse rates will be marginal, and it is not a favored time of day.
Steady easterly wind will lead to temperatures not moving much during this time. Still near to slightly below normal for late March though during the day. Night-time temperatures more likely to be above normal.
Long Term - Monday Night Through Saturday
Highlights... * Cool and cloudy with scattered showers (some mixed with graupel) on Monday. Some snow coatings possible in the hilly terrain Monday night.
* Continue to monitor potential mid to late-week coastal system. Consensus track remains south of Southern New England, but could bring rain/wet snow if it tracks closer to the coast.
* Brief break Friday night - early Saturday before a cold front arrives later Saturday.
* Cooler than normal temps (especially highs) through midweek, then trending closer to normal by late week/early weekend.
Details... Overall a fairly unsettled and (more often than not) cloudier weather pattern in store thru late week. Other than in cloud breaks, sunshine probably will be hard to come by over the next handful of days.
Upper low and its cool pocket of air aloft will meander from Ontario into interior New England on Monday. Considerable low-level moisture supports mostly cloudy conditions with scattered instability-type showers. While the convective depth is pretty shallow, steep lower- level lapse rates associated with cooler pocket of air aloft and low freezing levels could support graupel at times. Best chance for showers during the day is north and west of I-95. Quantitative Precipitation Forecast amounts should be limited to a tenth-inch or less, but just be aware that you'll have to dodge some showers at times.
Later Monday night, modest cool advection may help transition rain to wet snow showers particularly across the higher terrain. Could be some spotty light coatings in these areas (east slopes of the Berkshires, northern Worcester County and possibly into a part of the Merrimack Valley), but otherwise looking at a cloudy night with cool rain showers.
Abundant clouds and limited heating supports highs on the cooler end of guidance
Still unsettled into Tuesday, with a lingering inverted trough aloft interacting with some onshore moisture supporting a period of light rain or snow showers. At the surface, a cool wedge of high pressure builds down from ME/eastern NH on northeasterly flow. This will help reinforce the cooler air. Temperatures should trend cooler than normal, with highs in the low to mid 40s for most, though into the mid-upper 40s across Tolland and Hartford Counties.
Tuesday Night through Thursday Night:
Pattern change toward one of high-latitude blocking remains advertised for much of this period, with GFS/ECMWF (European Centre for Medium-Range Weather Forecasts) ensemble teleconnections indicating a negative-phase AO/NAO. By Tuesday night, the upper-level low initially over Nova Scotia and adjacent waters begins to retrograde back towards the Northeast US. Today's 12z guidance continues to advertise a southern- stream trough which leads to surface low developing over the lower MS Valley/Deep South on Tuesday, which progresses off the mid-Atlantic coast Wednesday. Where this coastal low evolves thereafter remains uncertain.
Currently, nearly all of the 12z deterministic model guidance traverses this coastal low eastward south of 40 deg N latitude, with little if any poleward/northward advance. Last night's 00z Canadian GEM operational run, however, did bring a coastal storm to Southern New England. It's southern stream disturbance was a lot stronger than the GFS or the ECMWF depiction. It is also worth noting this lone 00z Canadian GEM solution didn't have support from the GFS/ECMWF ensemble and even its own GEM ensemble. It has since gone back on the 12z run toward the consensus suppressed/southern track. The southern-stream trough responsible is forecast to come onshore coastal California later tonight, and while the model consensus currently favors little impact if any at all (at least an enhancement to NE winds over the southern waters), all outcomes still remain on the table and will not yet downplay this system. Will continue to advertise lower Chance-level Probability of Precipitation with nonetheless considerable cloudiness at least given the presence of the retrograding upper low and related moisture.
Will have to watch how close any wrap-around precipitation gets later Wednesday night into Thurs night, with the 12z ECMWF/Canadian GEM and to a lesser extent the GFS indicating this potential.
Temperatures Wednesday start off cooler than normal on the highs (in the mid to upper 40s), and near normal on the lows (in the 30s Tues thru Thurs night). By Thursday, highs should start to trend closer to normal (upper 40s-mid 50s).
Friday - Saturday:
There is some level of uncertainty in this period on shower chances on Friday depending on how close any wrap-around moisture makes it from the distant coastal system, which looks to slow/stall in the waters south of the Canadian Maritimes. Better chances may be towards the coast than further inland, but will stay close to a model blended approach which keeps chances for showers going across a larger part of Southern New England.
Nonetheless, even if drier weather ultimately ensues for Friday, most models show a cold front progressing in from the Great Lakes/OH Valley into Saturday, bringing another chance for showers. Seasonable to slightly above normal highs in the upper 40s to mid 50s with lows in the mid/upper 30s.
Tweaked the timing of Small Craft Advisories across the waters. Did not have enough confidence to issue such advisories for Boston Harbor and Narragansett Bay, but it is not impossible for some gusts to 25 kt on those waters Sunday. Low risk for gale force gusts across the eastern coastal waters late Sunday afternoon into Sunday evening. Not enough confidence in these gusts to upgrade to Gale Warnings. It's marginal.
Rain expected to develop tonight into Sunday as a warm front lifts through and a secondary low develops along the south coast. Some visibility reduction as fog develops, too. Winds will gradually shift to the east tonight and Sunday, then increase. On Sunday gusts will increase to 25- 30 kts along with seas building to 5-8 feet across the interior ocean waters, while the outer waters see waves build to 7-10 feet. Confidence has increased to issue a Small Craft Advisory across the majority of ocean waters through Sunday.
There is potential for isolated thunderstorms across the ocean waters Sunday evening.
Winds decrease and become more variable across most of the waters Sunday night as a secondary low pressure develops near Cape Cod.
Outlook /Monday Night through Thursday/... Monday: Winds less than 25 kt. Areas of rough seas. Scattered rain showers, patchy fog. Local visibility 1 to 3 nm.
Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Scattered rain showers, patchy fog.
Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Isolated rain showers.
Tuesday Night: Winds less than 25 kt. Areas of rough seas. Slight chance of rain showers.
Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers.
Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.
Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Slight chance of rain showers.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory from 5am early this morning to 2am EDT Monday for ANZ232. Small Craft Advisory from 5am early this morning to 10pm EDT this evening for ANZ233-234. Small Craft Advisory from 8am this morning to 2am EDT Monday for ANZ231. Small Craft Advisory until 8am EDT Monday for ANZ235-237-255- 256. Small Craft Advisory from 8am this morning to 8am EDT Monday for ANZ250-251. Small Craft Advisory from 5am early this morning to 8am EDT Monday for ANZ254.