textproduct: Boston / Norton

WHAT HAS CHANGED

Increases to rain chances and northeast wind speeds and gusts for Sunday into Monday for southeast New England. While these changes were minor, more significant increases could be needed pending the track of coastal low pressure to Southern New England.

KEY MESSAGES

- Increasing cloudiness today and generally dry with cooling onshore breezes, although light rain showers develop late today and tonight in western MA into portions of CT and southern RI.

- Coastal low pressure just to our south brings cloudy and cool weather, northeast breezes and periods of rain showers to southeast New England Sunday, possibly into Monday.

- Dry weather with onshore breezes resume early to middle of next week with a warming trend to temps, before weather turns more unsettled late in the week.

DISCUSSION

KEY MESSAGE 1...Increasing cloudiness today with cooling onshore breezes, although light rain showers develop late today and especially tonight for western MA and portions of CT and southern RI.

Sfc ridge in place across most of Southern New England will supply another round of modest onshore flow/seabreezes today, with cool temperatures in part from a upper-level low parked over the Canadian Maritimes. To our west is a stream of mid to high level moisture across western NY, which will be advancing across our area through today. Expect increasing cloudiness toward an overcast look by this afternoon, although for the vast majority of Southern New England, that "overcast" is really a pretty extensive canopy of mid to high cloud cover. With mid to high clouds and onshore flow, I kept highs on the cooler end of guidance in the mid/upper 40s for eastern MA and the South Coast, and lower to mid 50s further into the interior.

Although much of the area is dry today/tonight, the exception is in far western MA and adjacent Hartford County in CT, and eventually into Tolland County RI and southern RI late tonight. Showers associated with an initially weak mid-level shortwave trough over MI end up shifting ESE today, and some of those showers should be able to make it into western MA/Hartford County area late in the day (shortly before sundown), then expand ESE toward southern RI tonight. The eastern and northern extent of these showers should be stunted by northwesterly confluent mid-level flow and the drier air in place; most BUFKIT profiles show a pretty robust plume of dry air below 850 mb in central/eastern MA and northern RI. The NAM still remains a more bullish outlier on QPF, and even though the GFS did tick upward some, some of that QPF will be lost to saturate the profile. Offering periods of light rain from about Westfield to Willimantic south and west thru midnight, then expanding southeast towards southern RI/Newport area overnight. Possible that some of that could mix with wet snowflakes in the terrain in Tolland County but really not of much impact. High res guidance also shows a rather sharp precip cutoff, far more so than the coarser-res global models show and that probably is what transpires. This then sets us up for a lower-confidence forecast as we head into Sunday and Monday, to be addressed in the next Key Message.

KEY MESSAGE 2...Coastal low pressure just to our south brings cloudy and cool weather, northeast breezes and periods of rain showers to southeast New England Sunday, possibly into Monday.

Low pressure south of Long Island Sunday morning, on the southern periphery of the high pressure in place over New England, should still favor at least overcast with best chance for rain along the South Coast, Cape and Islands, to go along with enhanced NE winds. Devil's in the details and the main issue is how far north and how quickly will this low pressure get to at least southeast New England for Sunday and possibly into Monday. Seemingly key in that evolution is how quickly will the trough over MI today become entrained with the circulation over Atlantic Canada and close off. The NAM, SREF and to a more limited extent the 12z ECMWF show the trough closing off soonest, producing a slow-moving gale low south of Nantucket, which then slowly meanders NNE into Monday. Were this to verify, much of southeast New England would see a chilly, raw and wet Sunday and Monday with periods of rain and NE gusts to near gale force (e.g. NAM shows 950 mb NE winds 55-60 kt). The risk for rain in that outcome would also extend as far north as the Mass Pike, and especially eastern MA. Though I think it's too early to outright dismiss this, it doesn't have much support from the GFS/Canadian/more recent 00z ECMWF camp, which closes off the mid- level shortwave too late to a more offshore solution, keeping lighter rain showers to the coastal waters, Martha's Vineyard, Nantucket and Cape Cod with NE breezes, with mostly cloudy but generally dry conditions elsewhere for Sunday into Monday. Cluster analyses also suggest the NAM solution is more of an outlier. Will weight the forecast closer to the GFS/Canadian more offshore idea, but still shows chance to borderline likely PoP and NE winds increasing Sunday night into Monday for southeast New England. If other guidance were to come on board with the NAM in subsequent guidance, then the potential for more substantial forecast changes would be in the cards. Astro tides are decreasing so really no risk for coastal flooding. Highs in the 40s to lower-mid 50s Sunday, coolest southeast New England, and in the 50s to lower 60s for Monday, though in the lower 50s for eastern MA with NE breezes.

KEY MESSAGE 3...Dry weather with onshore breezes resume early to middle of next week with a warming trend to temps, before weather turns more unsettled late in the week.

High pressure then reasserts itself once the coastal low pulls away either Monday or Tuesday - viewed as more likely Monday. This brings what should be nice weather with onshore breezes and temperatures gradually modifying, although still slightly cooler than normal. Our weather pattern then turns more unsettled for mid to late in the week, with a possible risk for coastal cloudiness/rain showers Wednesday, and then troughing and a cold front around Thursday/Friday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Today and Tonight: High confidence.

VFR, increasing coverage of mid to high clouds. Ceilings start to lower to lower-end VFR/MVFR levels near BDL around 22-00z with rain showers. VFR visibility for most. Rain showers and MVFR ceilings then expand southeast to near PVD overnight. NE winds 5-10 kt shifting to SE late this morning into this afternoon, then becoming light southerly (calm at times) early tonight before returning back to NE 5-10 kt toward daybreak Sunday.

Sunday and Sunday Night: High confidence for most, but low to moderate confidence for the Cape and Islands.

BKN/OVC VFR for most, with NE winds 5-10 kt. Lowest ceilings/categories (MVFR levels) 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. If the low pressure were to track closer to Southern New England's waters, then ceilings would trend closer to IFR/LIFR, MVFR visby rain and NE winds in the 20 kt range for the Cape and Islands, with MVFR ceilings northward to the I-95 corridor, but this is viewed as unlikely.

KBOS Terminal...High confidence in TAF. VFR through the period. NE winds 5-10 kt trend to ESE by late morning, then shifting to light southerly (calm at times?) late tonight before returning back to NE overnight.

KBDL Terminal...Moderate confidence in TAF. VFR through at least late this afternoon. Ceilings lower to MVFR ranges with VFR visby rain showers 23-01z, which continue through 12z Sunday. ESE winds trend light southerly tonight, then return to ENE winds overnight.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local MVFR possible. Slight chance RA.

Sunday Night through Monday: VFR. Breezy. Slight chance SHRA.

Monday Night through Tuesday: VFR. Breezy.

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

MARINE

Forecaster Confidence Levels...

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

Today and 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, building to around 4 ft on southern waters. 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 and building seas, which could warrant SCAs on the southern waters if the low pressure passes closer to Southern New England's waters. NE winds around 10-20 kt northeast waters. Though it is unlikely, a period of stronger northeast winds possibly into the 30 kt range could develop Sunday night southeast of Cape Cod. Rain showers southern waters, but mainly dry eastern waters.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt. Chance of rain.

Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

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

Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

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

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

Wednesday: Winds less than 25 kt. Rough seas up to 8 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

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