textproduct: Boston / Norton

WHAT HAS CHANGED

Snow is coming to an end for eastern MA in the next 2-5 hours after some hyper localized snowfall this morning. Parts of northeast MA and southern RI where received around 12 and 9 inches respectively. Expected snow amounts have been lowered for the south shore of MA, while there have been no significant changes to the forecast dangerously cold wind chills tonight.

KEY MESSAGES

- After some hyper localized snowfall this morning, snow tapers off through 7pm except for Cape Cod and Nantucket where ocean effect snow continues overnight.

- Dangerous cold tonight into Sunday. Gusty winds produce wind chills as cold as 10 to 30 degrees below zero. High confidence in hazardous freezing spray over the waters.

- Quiet to start next week then another disturbance could bring unsettled weather mid to late week.

DISCUSSION

Key Message 1...After some hyper localized snowfall this morning, snow tapers off through 7pm except for Cape Cod and Nantucket where ocean effect snow continues overnight.

Well the very dynamic system we expected has lived up to expectations with hyper localized maxima over northeast MA and southern RI. A small strip in Essex county has received over a foot of snow while the immediate coast of RI received 8 inches by 10 am. The combination of mesoscale banding from surface convergence associated with the inverted trough, the arctic front, and ocean effect enhancement will continue to drop light to moderate snow for locations generally east of Worcester through 4-7 PM dropping an additional 1 to 3 inches between 1 PM and 7PM. The only place expected to see snow continue beyond around 7pm is Cape Cod and Nantucket where the favorable wind trajectory will lead to continued ocean effect showers through midnight, and even off and on through mid day Sunday. By the time all is said and 2 to 4 inches of snow is likely on Cape Cod with even some localized amounts over 4 inches.

Key Message 2...Dangerous cold tonight into Sunday. Gusty winds produce wind chills as cold as 10 to 30 degrees below zero. High confidence in hazardous freezing spray over the waters.

We continue to have high confidence that today's arctic front ushers in an anomalously cold airmass (925 mb temps as cold as -16C), accompanied by a strong LLJ (40-45 kts at 925mb), 30-40mph of which should mix down as strong gusts this evening into the overnight hours. The combination of strong winds and cold air will lead to dangerous wind chill temperatures on the order of -10 to -15F in eastern MA/RI and between -15 and -30 F in the highest elevations of the Worcester Hills and Berkshires. While these temperatures will bottom out around 7 am (with actual temps in the single digits +/- 0F) it will be a slow warm up, never feeling above the single digits during the afternoon. Some locations may not crack a wind chill above zero.

Key Message 3...Quiet to start next week then another disturbance could bring unsettled weather mid to late week.

The distant offshore low to our southeast continues its way out to sea for the start of the week and high pressure over the eastern Great Lakes builds in. Gusty winds from 20 to 30 mph persist through Sunday before the pressure gradient starts to weaken, and high pressure takes control of the pattern over southern New England Monday into Tuesday. Dry conditions make a return with continued below-normal temperatures, though Wednesday could see highs in the mid 30s. These are still below normal, but may feel much warmer than what we've dealt with lately.

We are continuing to monitor another possible system that could impact southern New England sometime midweek. Latest guidance still doesn't have a solid grasp on track or exact timing, which is not expected this far out. But generally, 925 mb temperatures could climb to around -5C and even 0C by Wednesday morning. A low from the NW may cross over the northeast that could lead to showers across southern New England. But again, it is too far out to know for certain and much can and will change between now and then.

AVIATION /19Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

This afternoon...Moderate confidence.

MVFR-IFR conditions in areas of snow with localized heavier snow bands and LIFR across eastern MA and RI terminals. Increasing N-NW winds from W to E with gusts to 25-35 kt developing.

Tonight...Moderate confidence in timing.

MVFR improves to VFR during the evening, except for Cape Cod and Nantucket where lower cigs/vsbys linger in ocean effect snow showers. NW wind gusts 25-35 kt. Occasional gusts on Cape Cod and Nantucket to 40 kt possible just before midnight.

Sunday...High confidence.

VFR. Gusty NW winds continue to gust 25-30 kts in the morning, decreasing to to 18-25 kts in the afternoon.

Outlook /Sunday Night through Thursday/...

Monday through Monday Night: VFR. Breezy.

Tuesday: VFR. Slight chance SN.

Tuesday Night: Mainly VFR, with local IFR possible. Chance SN.

Wednesday: Mainly VFR, with local MVFR possible. Slight chance SN.

Wednesday Night: VFR. Slight chance SN.

Thursday: VFR.

MARINE

Forecaster Confidence Levels...

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

Headlines:

* Gale Warnings from Sat afternoon into Sunday.

* Heavy Freezing Spray warnings for Saturday afternoon through early Mon morning.

Gusty N winds 30-40 kt this afternoon through tonight behind the arctic front. Areas of heavy freezing spray will develop tonight into Sunday as gusty gusty winds combine with arctic air moving into the region. Heavy freezing spray produces ice accretion rates up to 1 inch/hr creating very dangerous conditions for vessels though Monday morning. Seas peak around 8-12 ft tonight, decreasing to 6-8 ft by Sunday night.

Outlook /Sunday Night through Thursday/...

Monday: Winds less than 25 kt. Areas of rough seas.

Monday Night: Winds less than 25 kt. Seas up to 5 ft.

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of snow.

Tuesday Night: Winds less than 25 kt. Chance of snow, chance of rain.

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain, slight chance of snow.

Wednesday Night through Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Extreme Cold Warning from 6 PM this evening to 1 PM EST Sunday for CTZ002>004. MA...Extreme Cold Warning from 6 PM this evening to 1 PM EST Sunday for MAZ002>004-008>012. Winter Weather Advisory until 7 PM EST this evening for MAZ004- 005-012>021-026. Cold Weather Advisory from 6 PM this evening to 1 PM EST Sunday for MAZ005>007-013>023-026. Winter Storm Warning until 7 PM EST this evening for MAZ006- 007. Winter Weather Advisory until 1 AM EST Sunday for MAZ022>024. RI...Winter Weather Advisory until 7 PM EST this evening for RIZ001>008. Cold Weather Advisory from 6 PM this evening to 1 PM EST Sunday for RIZ001>008. MARINE...Gale Warning until 7 AM EST Sunday for ANZ230-236. Freezing Spray Advisory until 7 PM EST Sunday for ANZ230. Gale Warning until 1 PM EST Sunday for ANZ231-232-250-251-254. Heavy Freezing Spray Warning until 7 AM EST Monday for ANZ231>237-250-251-254>256. Gale Warning until 10 AM EST Sunday for ANZ233>235-237. Gale Warning until 1 PM EST Sunday for ANZ255-256.