textproduct: Boston / Norton

WHAT HAS CHANGED

The track of the coastal low to the south of southern New England looks to remain offshore, so chances for rain have been kept towards the south coast for Sunday.

KEY MESSAGES

- Cloudy with some light rain showers out towards CT and western MA this evening, then into southern RI and along the south coast tonight.

- Showers may linger towards the Cape and Islands tomorrow, but otherwise, cloudy and cool.

- Dry conditions early next week with temperatures around or slightly below normal. Trending unsettled and cooler mid to late- week with periods of rain, especially Thursday.

DISCUSSION

KEY MESSAGE 1...Cloudy with some light rain showers out towards CT and western MA this evening, then into southern RI and along the south coast tonight.

High pressure remains affixed over New England into tonight as a low pressure in the Mid Atlantic will continue progressing eastward. Rain showers associated with this low are already under way in parts of SW CT and NY, which will continue east through the rest of this afternoon into tonight. Showers will very likely impact the Hartford area and far western MA within the next couple of hours. These are expected to spread into southern RI tonight and to the Cape and Islands. Elsewhere, significant dry air will limit the chance for rain showers.

Cool air aloft (925 around 2C) and persistent cloud cover will help keep lows in the upper 30s across southern New England tonight. Given these temperatures, the risk for any mixed precipitation in any of theses overnight showers out in CT is very low to zero. A few wet snowflakes in the highest terrain could mix with rain later tonight, but confidence is very low in that occurring (plus, these would have no impact).

KEY MESSAGE 2...Showers may linger towards the Cape and Islands tomorrow, but otherwise, cloudy and cool.

Guidance has become clearer with regards to the track of this coastal low pressure. The 12z NAM moved back towards the solution the global guidance and other high res models were indicating, which was more of an offshore track that would limit any risk for showers for Sunday to the south coast, Cape Cod, and the Islands. High pressure remains fixed over New England through Sunday, helping keep the low off to our south. Onshore flow will continue, as well as more overcast conditions. This will keep highs for Sunday in the 50s with low 60s possible in the river valleys. As the low should remain further offshore, stronger wind gusts should also remain well offshore.

For Sunday night, cloud cover may start to clear out west as the low continues pulling offshore, but clouds would be lingering over eastern MA heading into Monday morning. Onshore flow continues and lows likely fall in the upper 30s to low 40s.

KEY MESSAGE 3...Dry conditions early next week with normal to slightly below normal temperatures. Trending unsettled and cooler mid to late-week with periods of rain, especially Thursday.

High pressure moves back into the region as surface low pressure pulls further offshore Monday. This will bring a period of dry conditions to start the week. Temperatures hover between normal to slightly below normal Monday/Tuesday with highs in the upper 50s to low 60s. The warmest temperatures will likely be found in the CT valley. Temperatures along the eastern coastal areas stay in the low to mid 50s reinforced by onshore flow.

Ensemble guidance shows a general consensus with a transition to a more unsettled pattern mid to late-week as an upper trough approaches from the north and east. Scattered showers are possible Wednesday as a piece of shortwave energy swings onshore, with the showers most favored along the coastal areas/east. The highest chances for more widespread showers/rain should be Thursday as a more consistent plume of above normal moisture arrives ahead of the approaching trough. Confidence lowers in the details with differences among model guidance with the evolution of the mid-level pattern and speed of the trough. Some solutions close off a 500 mb low and favor a slower exit of the system which could bring higher rain totals and showers lingering through the day Friday. For now, we can expect the highest probability of seeing widespread rain on Thursday/Thursday night with lingering showers possible on Friday. Not seeing any signal for excessive rainfall or flash flooding concerns at this time.

The trough and cold front push through by the start of the weekend with ensembles signaling at a below normal airmass settling across southern New England. This could another weekend of slightly cooler than normal temperatures.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

Rest of Today and Tonight: High confidence.

VFR. Satellite showing increasing mid to high level clouds this afternoon which should continue. Ceilings start to lower to lower-end VFR/MVFR levels near BDL around 20-23z with rain showers. VFR visibility for most. Rain showers and MVFR ceilings then expand southeast to near PVD overnight. SE winds this afternoon will persist into the evening, remaining below 10 kt. They then will shift SSW for some before going light and variable in some areas to calm. Rain showers are a possibility towards the Cape and Islands heading into Sunday morning.

Sunday and Sunday Night: High confidence.

BKN/OVC VFR for most, with NE winds 5-10 kt. Lowest ceilings (MVFR) and stronger NE winds around 10-15 kt for the Cape and Islands, to go along with periods of showers as low pressure passes to our south. Chances for showers may linger through Sunday night towards ACK.

KBOS Terminal...High confidence in TAF. Winds overnight may periodically go calm.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Slight chance SHRA.

Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA.

Wednesday Night: Mainly VFR, with local MVFR possible. SHRA likely.

Thursday: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

MARINE

Forecaster Confidence Levels...

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

Tonight: High confidence.

Winds and seas are below SCA criteria through tonight, with E/SE winds around 10-15 kt and seas 3 ft or less. Winds over the eastern waters may be more W, though will remain light. Dry weather today, although a risk for showers on the southern waters tonight.

Sunday and Sunday Night: Moderate confidence.

Coastal low pressure passes over the southern waters Sunday into Sunday night. Expect increasing northeast winds to around 20-25 kt well offshore and building seas, which could warrant SCAs on the southern waters towards Monday if the low pressure passes closer to Southern New England's waters. NE winds around 10 kt northeast waters. Rain showers over the southern waters, but mainly dry eastern waters.

Outlook /Monday through Thursday/...

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

Tuesday Night: Winds less than 25 kt. Areas of rough seas. Slight chance of rain showers.

Wednesday through Wednesday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.

Thursday: Winds less than 25 kt. Areas of rough seas. Rain showers likely.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.