textproduct: Boston / Norton

WHAT HAS CHANGED

Winter Weather Advisories posted for Tuesday afternoon to Wednesday morning for interior Southern New England for light accretion of icing and minor snow and sleet accumulation. There is also increasing confidence on a period of a wintry mix Thursday night into Friday across northern MA.

KEY MESSAGES

- Wintry mix of snow, sleet and freezing rain brings slippery roads to interior Southern New England Tue afternoon and evening; brief wet snow changes to plain rain and minimal to nil impact for the MA/RI coastal plain.

- Dry and very pleasant weather arrives Wednesday, feeling mild with March sunshine, light winds and highs in the upper 40s to lower 50s.

- A period of wintry precip remains possible Thu night into early Fri.

- Pattern change towards milder weather this weekend and potentially warmer next week.

DISCUSSION

215 PM Update:

KEY MESSAGE 1...Wintry mix of snow, sleet and freezing rain brings slippery roads to interior Southern New England Tue afternoon and evening; brief wet snow changes to plain rain and minimal to nil impact for the MA/RI coastal plain.

Quasi-stationary frontal boundary lying across the OH Valley and mid- Atlantic Piedmont region will lift northward on Tue, spreading clouds and warm-frontal precipitation northward into Southern New England Tue starting mainly during the early to mid-afternoon hours. This precip will be falling into a retreating modified-Arctic airmass coming out of another chilly night tonight. However the combination of onshore/east flow and associated warming surface temps along the coastal plain to go along with limited surface heating before turning overcast during the morning hours could offset evaporative/wet-bulb cooling until precip arrives. Given the now-delayed arrival of precip and questions on how soon arrival of clouds come in, how cold surface temps could still prove to be a challenge; utilized some of the colder 2-m temps given the potential for wet-bulbing which model-blended solutions tend to wash out or not resolve as well.

We still expect a wintry mix of snow/sleet/freezing rain in interior Southern New England during the afternoon and evening hours where winter weather advisories have been posted from Tue noontime til early Wed morning. The main impact in those areas is from icing, with up to a tenth of an inch of ice accretion, and up to an inch of combined snow/sleet accumulation at outset. It is somewhat debatable/uncertain how much road impact there may be during the Tue afternoon drive, and that's especially the case if cloud cover is slow to arrive and ends up permitting several hours of strong early-March sun to warm up pavement; feel more confident in at least slippery road conditions developing by the early evening hours, as temps hover or slightly cool on light NE drainage winds which will help sustain frozen p-types in interior Southern New England until precip comes to an end Wed morning.

In the coastal plain, a brief period of wet snow during the early to mid afternoon Tuesday should mix over with rain with temps in the mid 30s, then change to a plain rain for the remainder of the evening where adverse road impacts should prove minimal.

KEY MESSAGE 2...Dry and very pleasant weather arrives Wednesday, feeling mild with March sunshine, light winds and highs in the upper 40s to lower 50s.

Short wave ridging in fast flow aloft advects across SNE, providing a very pleasant, dry Wed across SNE. Mild with highs in the upper 40s and low 50s. It feel even milder given light winds and full March sunshine.

KEY MESSAGE 3...A period of wintry precip remains possible Thu night into early Fri.

Fast, wavy zonal upper air pattern yields the next precip event for SNE Thu night into Fri. 1040 mb anticyclone over southeast Quebec into the Maritimes will yield a wedge of shallow cold air into SNE. This will support the risk of a wintry mix this period, with highest probs of an icy mix across northern MA. It's possible this shallow cold air could bleed farther south, with a low risk of a wintry mix near or into the I-95 corridor. Just too early to tell, this needs to be watched. Not a major winter event, but it only takes a small amount of ice to impact travel. Stay tuned.

KEY MESSAGE 4...Pattern change toward milder weather this weekend and potentially warmer next week.

Good multi-model agreement on a pattern change beginning this weekend and continuing into next week, with a southeast/western Atlantic ridge. This will promote SW up the eastern seaboard into SNE, with temps rising into the low 50s Saturday, and possibly low 60s away from the south coast Sunday and Monday. Dew pts will be rising into the low 50s then, so definitely a mild feel to the airmass, along with accelerating the erosion of the the snow pack with dew pts rising into the 50s and SW winds 10-15 mph providing some mixing around the snowcover.

AVIATION /04Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

06z TAF Update...

Today and tonight...High confidence in trends with moderate confidence in timing.

MVFR-IFR conditions in mainly snow overspread the region from southwest to northeast in the 15z to 20z time frame. Ptype initially mainly snow but a quick change to rain from south to north occurs in the 21z to 01z timeframe along the coastal plain with perhaps a brief period of sleet during the transition. However...across portions of the interior temps near or just below freezing will result in snow/sleet transitioning to pockets of light freezing rain by early evening. IFR to LIFR conditions expected tonight with periods of rain along the coastal plain and pockets of light freezing rain across parts of the interior. Winds generally less than 10 knots today and tonight.

KBOS Terminal...High confidence in TAF. Snow arrives near of just after 19z and flips to rain by 23z with perhaps a brief period of sleet during the transition. Little impact on runways expected.

KBDL Terminal...High confidence in TAF. Snow arrives around 16z/17z and flips to light rain/freezing rain by 22z/23z with perhaps a period of sleet during the transition. Temps this evening will be near freezing...so impacts may be somewhat limited on runways but some icing can not be ruled out.

Wednesday...Moderate confidence.

MVFR-IFR with even localized LIFR conditions in low clouds/fog patches early Wed morning improve to VFR by Wed afternoon. It is possible fog could linger longer in low lying locations given very weak winds/poor mixing.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR. Slight chance SN.

Thursday: Mainly VFR, with local IFR possible. Chance RA.

Thursday Night: MVFR/IFR conditions possible. Breezy. Chance RA, FZRA likely.

Friday: MVFR/IFR conditions possible. Breezy. RA likely, FZRA likely.

Friday Night: MVFR/IFR conditions possible. Slight chance RA.

Saturday: Mainly VFR, with areas IFR possible. Breezy. Slight chance RA.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday Night...High confidence.

Winds and seas remain below small craft advisory thresholds through at least Tuesday afternoon, with south to southeast winds around 10-15 kt. Seas may begin to build late Tuesday night into Wednesday to around 4-6 ft on the southeast outer waters, which could prompt small craft advisories. Reduced visibilities possible in snow to rain Tuesday afternoon.

Outlook /Tuesday Night through Saturday/...

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain, slight chance of freezing rain.

Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain likely.

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain likely.

Friday Night through Saturday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Winter Weather Advisory from noon Tuesday to 7 AM EST Wednesday for CTZ002>004. MA...Winter Weather Advisory from noon Tuesday to 7 AM EST Wednesday for MAZ002>012-014-026. RI...Winter Weather Advisory from noon Tuesday to 7 AM EST Wednesday for RIZ001. MARINE...Small Craft Advisory from 10 PM Tuesday to 7 PM EST Wednesday for ANZ254>256.