textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Dry and seasonable weather continues for tonight and Wednesday.

- A chilly rain likely late Thu into Sat, with some snow possible in the higher elevations of MA/CT

DISCUSSION

KEY MESSAGE 1...Dry and seasonable weather continues for tonight and Wednesday.

Dry subsident W to NW flow continues into Wednesday as southern New England remains under a flattened mid-level ridge. A moisture- starved shortwave drops southward overnight. This will mainly bring a period of breezy conditions overnight, mainly along the coast and interior higher elevations overnight. This will also bring in a slightly cooler airmass aloft by Wednesday. At most, temperatures may be a degree or two cooler than Tuesday. Highs will likely rise into the low to mid 50s with the exception of the CT Valley with upper 50s in spots. Mid/upper level moisture will support some cloud cover mixed in with sunshine.

KEY MESSAGE 2...A chilly rain likely late Thu into Sat, with some snow possible in the higher elevations of MA/CT

Good model (AI and traditional models) agreement on a coastal low or series of lows tracking somewhere along or south of New England in the Thu-Sat timeframe. Although, there is considerable uncertainty in the guidance on multi waves vs one consolidate low, along with the magnitude/intensity of each wave. Therefore, large differences on QPF, axis of heaviest QPF, along with location/track of dry slot. As for ptype, given the lack of cold air (warm blyr), most of the region will likely experience a chilly rain, especially the coastal plain and big population centers of Boston, Worcester, Providence and Hartford. For snow in the coastal plain to occur with this setup, a stronger system would be required, with strong height falls cooling the column from top down to erode warm boundary layer. Also, heavy precip would be required to cool the column via diabatic cooling from melting, and models show a very large spread in axis of heaviest QPF. Thus, a low confidence forecast on exact storm details. As for timing of precip, most 12z guidance, including the 12z REFS, Thu may begin dry, but by days end, most guidance has rain falling over all of MA/CT/RI.

A look at the ensembles, both AI and traditional models, only one or two members from both the EC and GFS ensembles have substantial snowfall across MA/CT/RI. Thus, non-zero, but very low probability of this happening. Again, it would require a stronger system with significant height falls and heavy precip over SNE. Hence, a chilly rain for most of MA/RI/CT, with some snow possible across the higher elevations of MA/CT.

As for snow probs from the ensembles, the 12z GEFS ensembles only have 10-20% probability for 3+ inches across Northern Worcester and the Berkshires. The CMC ensembles are very similar and the 12z ECENS have up to 50-60% of 3+ inches across the Berks, with 30-40% over Northern Worcester county.

Ensembles suggest low slowly exits by Sunday, with some height rises over SNE. Thus, some improvement Sunday with drier weather and not as chilly as Sat, although remaining blustery Sunday. Additional improvement comes early next week with further height rises promoting seasonable temps (highs low 50s) and dry weather.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

00z TAF Update...

Tonight...High confidence.

Mainly VFR conditions for the rest of today and tonight. W to WNW winds at 8-12 kts. A brief period of sporadic gusts near 18 kts is possible tonight after midnight around BOS and ORH. Otherwise, Cape/Islands may see gusts linger into the overnight period.

Wednesday...High confidence.

VFR conditions. SCT to BKN mid to high level clouds. Winds WNW at 8-10 kts.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Sunday/...

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

Thursday Night: Mainly VFR, with areas IFR possible. Windy with local gusts up to 30 kt. RA.

Friday: MVFR/IFR conditions possible. Windy with gusts up to 30 kt. RA.

Friday Night: Mainly VFR, with local IFR possible. Windy with local gusts up to 30 kt. Chance RA, chance SN.

Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance RA.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance RA.

Sunday: Mainly VFR, with local MVFR possible. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday night...High confidence.

Surface high pressure across the coastal waters tonight and Wednesday. Elevated winds continue this evening and early tonight as a dry front moves through with gusts 20-28 kts. Opted to keep the SCAs going for the outer southern waters and eastern waters since it is marginal. Seas 3-6 ft. Winds decrease early Wednesday morning, although seas may remain near 5 ft across portions of the southern outer waters through the afternoon Wednesday. SCAs will continue tonight through 12Z, but it is possible some of the southern zones may need to be extended due to the elevated seas.

Outlook /Wednesday Night through Sunday/...

Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of rain.

Thursday Night: Moderate risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Rough seas up to 11 ft. Rain.

Friday: Strong winds with gusts up to 35 kt. Rough seas up to 10 ft. Rain.

Friday Night: Strong winds with gusts up to 30 kt. Rough seas up to 11 ft. Rain likely.

Saturday: Strong winds with local gusts up to 30 kt. Rough seas up to 9 ft. Rain likely.

Saturday Night: Strong winds with local gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain.

Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 AM EST Wednesday for ANZ250- 254>256.