textproduct: Boston / Norton

WHAT HAS CHANGED

The High Wind Watch previously issued was upgraded to a High Wind Warning for the Worcester Hills and the eastern slopes of the Berkshires. The rest of southern New England is under a Wind Advisory. Both headlines start at 7 PM tonight and run through Tuesday night.

KEY MESSAGES

- Strong to damaging wind gusts tonight through Tuesday night. Strongest winds expected over western and central MA.

- Extended period of below normal temperatures tomorrow through Sunday. Nuisance snow showers at times, mainly New Years Eve night, but all in all, a cold and dry late week to the first couple days of the New Year.

- Vessel icing due to accretion of light freezing spray over the waters is possible this week into the weekend.

DISCUSSION

230 PM Update

KEY MESSAGE 1...Strong to damaging wind gusts tonight through Tuesday night, with the strongest winds expected over western and central MA.

Rain this afternoon will continue to push across the region this afternoon ahead of a cold front. Behind the front, strong cold air advection takes hold and gusty winds pick up with deep mixing and strong lapse rates. Wind gusts are expected to peak around mid morning, then slowly drop off as the day goes on. Occasional light snow showers are possible tomorrow over western MA as some of the lake effect snow well to our west moves across NY. Nothing more than a coating at most is expected with any of these.

Forecast soundings continue to mix up to 850 mb across much of southern New England, with winds at that point for most around 55 kt. Some soundings, particularly over the Worcester Hills and the eastern slopes of the Berkshires, mix up to 825 mb and tap in to the low level jet a bit more. Lapse rates after midnight tonight start to increase to around 8 C/km up to 10 C/km by early Tuesday afternoon. Even with the winds seeming more borderline between Wind Advisory and High Wind Warning criteria, it is worth noting that as the low pressure continues east, it is still expected to deepen, which will only strengthen the pressure gradient over the region and intensify winds as a result. So, with this in consideration along with downsloping, we went ahead and upgraded the High Wind Watch to a High Wind Warning over the eastern slopes of the Berkshires and across the Worcester Hills. The rest of the region was flipped to a Wind Advisory for the risk of gusts between 40-50 MPH.

KEY MESSAGE 2...Extended period of below normal temperatures tomorrow through Sunday. Nuisance snow showers at times, mainly New Years Eve night, but all in all, a cold and dry late week to the first couple days of the New Year.

Today (Monday) will be the mildest day for the foreseeable future, because while not record-setting cold, we are looking at a prolonged stretch of below normal temperatures which begin Tue and continue into at least the first weekend of the New Year. 500 mb pattern across CONUS becomes quite amplified and resembles a positive Pacific North-American (PNA) pattern with high-amplitude midlevel ridge over the West Coast/Intermountain West and downstream lower- than-normal heights/troughing across the Great Lakes, Ohio Valley and Northeast. It's a pattern which loads the dice toward reinforcing shots of cold, modified-Arctic air in the NW flow until the pattern breaks down, with weak-amplitude Clipper systems being favored, not amounting to much in the snow department.

Our 850 mb temps stay at or colder than -15C starting Tue into the weekend. Expect several days of highs in the 20s to values near freezing mark for the south coast, with lows in the single digits to the mid/upper teens.

As for precipitation/snow chances, the cold will be accompanied by generally dry weather. A reinforcing cold front New Years Eve night to early New Years Day could bring some decorative passing snow showers but significant/notable accumulation isn't likely.

KEY MESSAGE 3...Vessel icing due to accretion of light freezing spray over the waters is expected this week into the weekend.

Mostly for marine interests...but with a prolonged period of cold air over the relatively milder ocean waters, periods of freezing spray could accrete on vessel masts through much of this week. It doesn't look like anticipated freezing spray on any particular day would reach the moderate to heavy icing range which would necessitate freezing spray headlines for the waters, and days which have lower significant wave heights would have a lesser risk. However we did want to give it at least a mention, since the risk for light vessel icing due to freezing spray could exist for a prolonged period given the spell of colder temperatures upcoming.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

00z TAF Update:

Tonight and through Tuesday Night: High confidence.

Categories have improved to VFR in many locations. Ceilings could flirt with MVFR levels with hit- or- mostly-miss SHSN in the higher terrain at times into Tue. Marked increase in WNW gusts tonight to 25-35 kt; then becoming gusty to strong by Tues, increasing to 35-45 kt in all areas, with possible gusts to 50 kt at ORH.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...

Wednesday: VFR. Breezy. Slight chance SN.

Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SN.

New Years Day: VFR. Breezy. Chance SN.

Thursday Night through Friday: VFR. Breezy.

Friday Night through Saturday: VFR.

MARINE

Forecaster Confidence Levels...

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

- Strong Gale Force Wind Gusts and light freezing spray tonight through Tuesday night

Tonight through Tuesday night...

A cold front passes through this evening over the waters. Behind it, gale-force W wind gusts up to 45 kt amidst strong cold air advection move in tonight and continue through Tuesday night. Occasional gusts to 50 kt cannot be ruled out. Light freezing spray is another concern tomorrow through tomorrow night, though this risk is also expected to persist through the week.

Outlook /Wednesday through Saturday/...

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of snow.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of snow, chance of rain. Local visibility 1 to 3 nm.

New Years Day: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of snow, chance of freezing spray.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of freezing spray, slight chance of snow.

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow.

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

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Wind Advisory until 1 AM EST Wednesday for CTZ002>004. MA...Wind Advisory until 1 AM EST Wednesday for MAZ003-005>007- 010>024. High Wind Warning until 1 AM EST Wednesday for MAZ002-004-008- 009-026. RI...Wind Advisory until 1 AM EST Wednesday for RIZ001>008. MARINE...Gale Warning until 1 AM EST Wednesday for ANZ230-236. Gale Warning until 7 AM EST Wednesday for ANZ231-250-251-254. Gale Warning until 7 AM EST Wednesday for ANZ232>235-237-255- 256.