textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Wintry mix along and north of I-90 and in the high terrain winds down by early-mid morning...as well the burst of plowable snowfall expected in north central/northeast MA. A slippery early morning commute in these locations. Otherwise...areas of fog, spotty very light rain/drizzle may persist at times today & tonight. Any light freezing drizzle confined mainly to the high terrain this afternoon, but black ice may become more of a concern across the rest of the region tonight.

- Turning milder with a warming trend this weekend and with risk for showers Sat night into early Sun.

- Potential for a few days of unseasonably mild conditions next week but have to watch a backdoor front to the north which would bring much cooler temps. Accelerated snowmelt will lead to steady rises on rivers and streams through the week. A period of showers accompany a cold front late Wed-Thu, then turning cooler towards the end of the week.

DISCUSSION

KEY MESSAGE 1...Wintry mix along and north of I-90 and in the high terrain winds down by early-mid morning...as well the burst of plowable snowfall expected in north central/northeast MA. A Slippery early morning commute in these locations. Otherwise...areas of fog, spotty very light rain/drizzle may persist at times today & tonight. Any light freezing drizzle confined mainly to the high terrain this afternoon, but black ice may become more of a concern across the rest of the region tonight.

The forecast remains on track early this morning. Rain and freezing rain have changed to mainly sleet along and north I-90 early this morning. This a result of 925T between -2C and -4C and the depth of the cold layer between 4-5K feet. So the main risk for a very localized areas of 0.25"+ of ice accretion will be in the southern Berks/southern Worcester Hills and the highest locations of the CT Hills. Fortunately...this risk looks to be very localized but power outages are possible if these higher ice amounts are realized.

High resolution CAMS still indicate a period of 20-30 units of lift in the snowgrowth region across north central and especially northeast MA until 5-6 am. Given the soundings are isothermal... intense lift will be needed to flip the sleet over to mainly snow. The HREF/HRRR/RRFS all indicating a window for brief 1" per hour snowfall rates possible through 6 am. A quick 2-4" of snow possible in this region with localized 5-6" amounts not out of the question in far northeast MA near the NH border. As we mentioned...the risk of the heaviest snow will be until 6 am with the threat of accumulating snow ending by 8-9 am in this region.

Otherwise...low pressure moves east of the region today but it will combined with high pressure over the Canadian Maritimes. So although the deeper/moisture forcing will have departed...persistent moist northeast flow will result in dreary weather continuing the rest of today into tonight. Spotty areas of very light rain/drizzle and fog will also remain possible at times. Temps will remain in the 30s today...but they should generally rise above freezing today outside the highest terrain so road conditions will improve later this morning and afternoon in areas impacted by the snow and ice early this morning. W still need to watch for spotty freezing drizzle and slippery travel into this afternoon in the highest terrain...mainly at elevations over 1000 feet in the Worcester Hills/Berks. Perhaps some black ice becomes more of an issue for the rest of the region tonight with temps dropping to near freezing.

Key Message 2...Turning milder with a warming trend this weekend and with risk for showers Sat night into early Sun.

A mid-level ridge/surface high moves into the western Atlantic this weekend directing milder S-SW flow into the region. While mid level temperatures surge (850mb temps as high as 13C) poor mixing with an inversion just off the deck will keep us from tapping into the truly mild temps. Even so, compared to highs in the low to mid 30s on Friday, Saturday will be warmer simply thanks to the winds at the surface flipping from NE to S/SW. Expect a cloudy day with highs in the mid 40s. A cold front then swings through Sunday, and out ahead of that the combination of a 50-60 kts LLJ and a 1.25"+ PWAT plume will lead to scattered light showers. The best consensus for timing is overnight Saturday but still need to get some higher resolution guidance to increase confidence, as some guidance wants to keep shower chances around through the day on Sunday. The best chance for this is southeast MA/coastal RI. For now sticking with thinking that showers and clouds clear out later Sunday allowing temps to further increase well into the 50s.

Key Message 3...Potential for a few days of unseasonably mild conditions next week but have to watch a backdoor front to the north which would bring much cooler temps. Accelerated snowmelt will lead to steady rises on rivers and streams through the week. A period of showers accompany a cold front late Wed-Thu, then turning cooler towards the end of the week.

The warm advection pattern continues through at least Tuesday before our next frontal system brings rain and colder temps mid week. We continue to see signals for highs well into the 60s by Tuesday but, as is fairly typical this time of year, a high pressure over eastern Canada may send a back door cold front into SNE around late Tuesday. This has the potential to spoil the warm temperatures early, especially for northeast MA. It could be a situation where we have a very large temperature gradient between northeast MA and southwest CT. Either way, confidence is higher that a cold front moves through with precipitation and a cooler airmass around Wednesday. Before that, though, increased temps and dewpoints will lead to significant loss of our snowpack, so will have to monitor for rises on rivers and streams.

AVIATION /07Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

06z TAF Update...

Today...High confidence.

IFR/LIFR conditions dominate today. Lingering rain changes to freezing rain and sleet in areas along and north of I-90 as well as parts of the high terrain over the next few hours. Sleet will be favored over freezing rain to the north of I-90 overnight with a change over to a burst of snow across north central and especially northeast MA likely during the time of the heaviest precipitation. The threat of accumulating snow/sleet across north central and northeast MA will come to an end by 13z/14z. Meanwhile...south of I-90 in the lower elevation, ptype mainly will be rain but some sleet may be mixed in at times.

All precipitation tapers to mainly spotty light rain/drizzle by mid- late morning. However...IFR/LIFR conditions likely persist along with areas of fog due to continued onshore flow. Any spotty freezing drizzle will mainly be confined to the highest terrain by late morning and afternoon. NE winds 5 to 15 knots with some 20-25 knot gusts possible near the coast and up to 30 knots or so for parts of the outer-Cape and Nantucket.

Tonight...High confidence.

IFR-LIFR persist. Winds slacken, but remain NE. Areas of spotty light rain/drizzle and fog persist at times. We may have to watch for spotty freezing drizzle/black ice with temps flirting with 32 degrees.

KBOS Terminal...High confidence in TAF. The threat for accumulating snow/sleet will come to an end by 13z/14z.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday: Mainly IFR, with local MVFR possible. Breezy. Areas BR, chance FZDZ, slight chance FZRA.

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

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance RA.

Sunday Night: VFR.

Monday through Monday Night: VFR. Breezy.

Tuesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Today and tonight...High confidence.

Large high pressure over the Canadian Maritimes coupled with low pressure to the south of the waters will continue to generate NE wind gusts of 20 to 30 knots and 4 to 8 foot seas today. Small craft headlines posted for all open waters today. The gradient/NE winds slacken tonight...but will need to continue small craft headlines for all outer-waters given long NE fetch and lingering swell.

Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt. Areas of rough seas. Patchy fog.

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

Sunday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain.

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

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

Tuesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Winter Weather Advisory until noon EST today for CTZ002>004. MA...Winter Weather Advisory until noon EST today for MAZ002>015- 026. RI...Winter Weather Advisory until noon EST today for RIZ001-003. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231>235-237. Small Craft Advisory until 7 PM EST Saturday for ANZ250-251- 254>256.