textproduct: Boston / Norton

WHAT HAS CHANGED

Given increased confidence in a high-impact winter storm, a Blizzard Warning has been issued for all of RI and eastern MA, including Boston and Providence. All other Winter Storm Watches have been converted to Winter Storm Warnings, except at Nantucket, where a Winter Storm Watch continues, given the uncertainty of rain mixing with the snow at times. Greatest impacts are expected in RI and eastern MA, with highest snow totals and strongest winds.

A High Wind Warning has been posted for Nantucket Sunday night into Monday night.

KEY MESSAGES

- A powerful winter storm brings significant impacts to much of the region Sunday night into Monday, with heavy snowfall, strong winds and blizzard conditions to RI and eastern MA.

- A powerful coastal storm will bring minor to moderate coastal flooding during the late Sunday night/early Monday morning high tide across eastern MA. The greatest impacts will be from Plymouth county southward to Cape Cod and the Islands.

DISCUSSION

KEY MESSAGE 1...A powerful winter storm will impact SNE with heavy snow, strong winds, blizzard conditions and coastal flooding Sunday night into Monday. Here are specific details -

Timing: light snow/flurries will develop Sunday afternoon across CT/RI/MA, however the accumulating snow will begin late Sunday/Sun evening. Then the heaviest snow will occur from late Sunday night into Monday afternoon. Very strong forcing for ascent results in bomogenesis, with multiple model guidance indicating the cyclone will intensify to sub 970mb as it crosses near the 40N/70W benchmark Monday! Model cross sections and soundings have very strong lift in the DGZ along with steep lapse rates, yielding bands of very heavy snow late Sunday night into Monday. The 12z HREF has mean hourly snowfall rates of 3+ inches around 12z Monday over RI and southeast MA! Given the magnitude of the lift and instability, low prob of thundersnow. Intensity of the snow should slacken late in the day Monday and especially Monday evening.

Snow amounts: all model guidance has at least an inch of qpf across RI and southeast MA, with some of the guidance over 2 inches in this region. Thus, very high confidence in at least a foot of snow across RI and southeast MA, with potentially up to 2 feet if these higher scenarios verify. Farther west into CT and western-central MA, some uncertainty how far northwest this heavy qpf rotates. Nonetheless, high confidence for 8-15 inches for CT and western-central MA, therefore Winter Storm Watches have been converted to warnings. Depending on the exact track of the low, rain may mix in a times across Nantucket. Therefore, some uncertainty on 6+ inches here. Hence, we held with the Winter Storm Watch. This will be a heavy/wet snow especially across RI and southeast MA.

Strong to Damaging Winds: a very strong low level NE jet up to 80 kt will traverse RI and eastern MA. Model soundings from both the NAM and GFS support gusts up to 45-55 mph, but as high as 70 mph possible across Cape Cod and the Islands! These wind speeds combined with the heavy snowfall rates will create white out conditions at times, hence a blizzard warning has been issued for RI and eastern MA. If the low trends farther west, blizzard warnings may need to be expanded into the Worcester Hills. Also, the combination of strong winds and heavy wet snow will yield the possibility of power outages across RI and eastern MA. For Nantucket, issued a high wind warning, as model soundings and cross sections have 70 kt of wind aloft extending downward to 500 ft!

Impacts: Heaviest snow and strongest winds are expected from roughly late Sunday night/early Monday morning into Monday afternoon. Travel will be nearly impossible, with snowfall rates 2-4" per hour at times during this period. Also, heavy wet snow will combine with strong winds, yielding the potential for power outages across RI and eastern MA.

KEY MESSAGE 2...Coastal Flooding

A storm surge of 2-3' at the time of high tide early Monday morning (2AM-5AM) will likely yield moderate coastal flooding from Plymouth county southward to Cape Cod and the Islands. Therefore a coastal flood warning has been issued for this portion of the coastline. Farther northward from Boston to the NH border, there is more uncertainty, with a higher probability of minor flooding likely. Therefore, we held with a coastal flood watch there. The greatest storm surge (up to 4 ft) appears to occur during low tide Monday (9- 10AM). However, there could be enough storm surge for minor coastal flooding during the late day high tide (3-6pm). Although, given the astro tide is lower and winds will be more northerly, only expecting minor flooding. Nonetheless, a coastal flood watch remains in effect for this second tide Monday to account for any storm track changes, including timing.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

Rest of Tonight and Sunday...Moderate confidence.

MVFR with IFR for ORH and pockets of VFR in NE MA. Light snow showers possible tonight mainly across western MA and CT. MVFR CIGS remain Sunday with light ENE winds. Snow showers wind down between 08 and 10z.

Sunday Night: High Confidence

MVFR turning IFR as light snow overspreads the region between 22-04z. Winds become gusty out of the NE at 15-20 knots. Snow rates pick up overnight sunday becoming very heavy at times. Winds increase overnight with gusts of 50-70 knots possible in eastern MA/RI esspically for the Cape and Islands. Significant LLWS with 70 knots of wind down to 500 feet.

KBOS Terminal...Moderate confidence in TAF.

Mainly MVFR tonight, however periods of VFR possible. MVFR moves back in for Sunday with increase SE winds. Snow should hold off until after 04z Monday. Snow quickly becomes heavy with hourly rates greater than 1" likely after 10z. Blizzard conditions expected with gusts up to 50kts by daybreak Monday.

KBDL Terminal...Moderate confidence in TAF.

MVFR for the TAF period. Light snow reaches the terminal Sunday around 00z. Snow quickly becomes heavy with hourly rates greater than 1" likely after 06z.

Outlook /Monday through Thursday/...

Monday: Mainly IFR, with areas MVFR possible. Strong winds with gusts up to 55 kt. SN, areas FG.

Monday Night: Mainly VFR, with local MVFR possible. Strong winds with gusts up to 45 kt. Chance SN.

Tuesday: VFR. Windy with local gusts up to 30 kt.

Tuesday Night: VFR. Breezy. Slight chance SN.

Wednesday: MVFR/IFR conditions possible. Breezy. Chance SN, chance RA.

Wednesday Night: Mainly VFR, with local IFR possible. Chance RA, chance SN.

Thursday: VFR. Breezy. Chance RA.

MARINE

Forecaster Confidence Levels...

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

Tranquil weather tonight, with a ridge of high pressure over the waters. Then a very powerful storm develops off the Mid Atlc coast Sunday, rapidly intensifying Sunday night and Monday into a dangerous storm, as it moves near the 40N/70W benchmark. This storm will be accompanied by very strong winds up to 60 kt and seas 15-25 ft across the RI and MA waters. Heavy snow will reduce vsby to near zero at times Sunday night and Monday. The storm exits into the maritimes Monday night, with improving weather conditions Tuesday and beyond.

Outlook /Tuesday through Thursday/...

Monday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 28 ft. Chance of snow. Local visibility 1 nm or less.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 13 ft. Chance of freezing spray.

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

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain, chance of snow. Local visibility 1 to 3 nm.

Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain.

Thursday: Winds less than 25 kt. Areas of rough seas. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Winter Storm Warning from 4 PM this afternoon to 7 AM EST Tuesday for CTZ002>004. MA...Winter Storm Warning from 4 PM this afternoon to 7 AM EST Tuesday for MAZ002>006-008>012-026. Blizzard Warning from 4 PM this afternoon to 7 AM EST Tuesday for MAZ007-013>023. Coastal Flood Watch from late tonight through Tuesday morning for MAZ007-015-016. Coastal Flood Warning from 1 AM to 7 AM EST Monday for MAZ019- 022>024. Winter Storm Watch from this afternoon through Tuesday morning for MAZ024. High Wind Warning from 10 PM this evening to 1 AM EST Tuesday for MAZ024. RI...Blizzard Warning from 4 PM this afternoon to 7 AM EST Tuesday for RIZ001>008. MARINE...Storm Warning from 10 PM this evening to 1 AM EST Tuesday for ANZ230>237-250-251-254>256.