textproduct: Boston / Norton

WHAT HAS CHANGED

The risk for wintry precipitation is lower for Thursday but several days of cool, overcast and raw weather look to be in store for late week into the first weekend in April.

KEY MESSAGES

- Breezy and unseasonably mild Monday away from the south coast.

- Period of above normal temperatures Tuesday and Wednesday, with a chance for low to mid 70s highs on Wednesday. Nighttime lows Tuesday night could be significantly above normal. Cold front moves in Wednesday afternoon and night bringing showers and a low chance for a rumble or two of thunder.

- Overcast, cool and raw weather Thursday through Saturday on northeast winds. Intermittent rain showers possible but better chance for rain on Friday as frontal boundary shifts southward.

DISCUSSION

KEY MESSAGE 1...Breezy and unseasonably mild Monday away from the south coast.

High pres moves offshore tonight and Monday with SW flow continuing. This will result in a milder night tonight and an unseasonably mild day Mon in the interior valleys. 925 mb temps increase to 8-10C so temps should reach the mid-upper 60s across CT valley and interior NE MA with mid 50s along the south coast. Dry weather expected through Mon although there will be enough mid-high clouds around to limit sunshine at times but overall a partly sunny day expected. It will also be rather breezy, especially near the coast as a 40-60 kt low level jet develops. The jet is above a low level inversion which will prevent these stronger winds from mixing down but soundings show a shallow mixed layer supportive of 25-35 mph gusts.

A backdoor front will push south from northern New Eng and may get into NE MA by Tue morning. Continued SW flow and advection of higher dewpoint air into SNE will result in areas of stratus developing and can't rule out patchy drizzle overnight along with a few showers as higher PWATs move in. Cloud cover and SW flow will keep low temps in the 40s to near 50 in the CT valley.

KEY MESSAGE 2...Period of above normal temperatures Tuesday and Wednesday, with a chance for low to mid 70s highs on Wednesday. Nighttime lows Tuesday night could be significantly above normal. Cold front moves in Wednesday afternoon and night bringing showers and a low chance for a rumble or two of thunder.

Challenging temperature forecast for Tuesday as a backdoor cold front tries to slip southward out of NH/ME into northern MA, while increasingly milder southerly flow builds into CT and western MA. Considerable cloudiness in all areas though, but nebulous forcing (better to our north and west), a modest increase in PWATs with drier air aloft probably favors very light rain or drizzle. Daytime max temps could struggle to get into the low 50s Tuesday in NE/eastern MA, but the further south and west one goes, better chance at highs in the 60s.

The warmer air aloft advecting in eventually wins out though, as southerly winds and continued overcast allow for a mild and increasingly moist Tue night. Highs for the day in NE MA could occur closer to midnight, but elsewhere, temps may not fall very far and/or rise some with values in the mid 50s. Potential exists for one of the milder nights we've seen in a while, and there's a chance sites like Hartford, Springfield and surrounding towns stay above 60 degrees for lows.

Coming out of a likely very mild and breezy Tuesday night, Wednesday still looks to be a quite mild day away from the south coast as 850 mb temps warm to +10 to +12C and 925 temps sit around 14 to +17C. Potential exists for highs in the mid 70s in some of the usually warmer spots (CT Merrimack Valleys) with upper 60s/low 70s elsewhere away from the south coast where highs will be kept cooler in the 50s/lower 60s given SW winds off the water. How warm we ultimately get will depend on the still-unclear timing of a cold front that will be shifting southeastward. Front also brings a better chance for at least showers, but with a low chance for a rumble or two of thunder based on narrow CAPE profiles with surface-based CAPEs around 500 J/kg. Front should have made it into the southern waters by overnight, with temps on the downswing into the upper 30s to mid 40s as the front moves south.

KEY MESSAGE 3...Overcast, cool and raw weather Thursday through Saturday on northeast winds. Intermittent rain showers possible but better chance for rain on Friday as frontal boundary shifts southward.

The late-week/early weekend period is the cooler, overcast and raw portion of the forecast. Increasing NE winds as shallow near-surface colder air filters southward, but temps aloft remain quite warm under SWly 850-500 mb flow with 925 mb temps around +2 to +8C. Although the threat for wintry precipitation looks minimal now, this pattern will maintain low clouds with intermittent showers and likely lead to a pretty raw day on Thurs. NBM temps in the mid 40s to low 50s are almost certainly too optimistic following its typical diurnal temperature curve, and that's very probably not appropriate given overcast and persistent NE winds. Plenty of room to go lower on temps in future updates but potential exists for widespread upper 30s to mid 40s with NE winds Thurs around 10-15 mph. Temps probably not going very far either Thurs night or Fri with highs in the mid 40s, with a better shot at widespread rain Fri as a cool front moves in from NY.

We again repeat the same weather pattern Sat as the same one from Thurs, with shallow cool air on NE winds and persistent low clouds under a continued mild profile of air aloft.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

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

Through Monday...High Confidence.

VFR. SW gusts to 25 kt drop off tonight then redevelop Mon with gusts to 25-30 kt. Areas of LLWS develops late tonight and Mon over the Cape/Islands with a strengthening low level jet.

Monday Night...Moderate Confidence.

Areas of MVFR-IFR stratus developing, first over the Cape/Islands during the evening then expanding inland overnight. Timing of lower cigs and areas extent is uncertain. A few showers or patchy drizzle developing overnight.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: Mainly MVFR, with local IFR possible. Breezy. Slight chance RA.

Tuesday Night: Mainly MVFR, with areas VFR possible. Windy with gusts up to 35 kt. Slight chance RA.

Wednesday: Mainly MVFR, with areas VFR possible. Windy with gusts up to 35 kt. Chance RA, isolated TSRA.

Wednesday Night: Mainly MVFR, with areas VFR possible. Breezy. Chance RA, isolated TSRA.

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

Thursday Night: Mainly MVFR, with areas IFR possible. Breezy. Chance RA.

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

MARINE

Forecaster Confidence Levels...

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

Persistent gusty SW winds will continue into Monday. Winds may briefly drop off a bit tonight, but increase again Mon with gusts up to 30 kt. The gusty winds will linger into Mon evening over the south coastal waters before diminishing as the LLJ moves offshore. We extended the SCA into Mon night as hazardous seas linger after the winds drop below SCA.

Outlook /Tuesday through Friday/...

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain. Local visibility 1 to 3 nm.

Tuesday Night: Strong winds with gusts up to 35 kt. Rough seas up to 13 ft.

Wednesday: Strong winds with gusts up to 35 kt. Rough seas up to 12 ft. Chance of rain, isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain, isolated thunderstorms.

Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain.

Thursday Night through Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Monday for ANZ230-236. Small Craft Advisory until 11 PM EDT Monday for ANZ231-250-251. Small Craft Advisory until 2 AM EDT Tuesday for ANZ232>234. Small Craft Advisory until 8 AM EDT Tuesday for ANZ235-237- 254>256.