textproduct: Boston / Norton

WHAT HAS CHANGED

Warm Wednesday but the spatial extent of 70 degree or greater temperatures appears to be less than previous forecast updates

KEY MESSAGES

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

- Increasing risk for rainfall tonight into Tuesday. Above normal temperatures continue.

- Period of above normal temperatures peaks on Wednesday, with a chance for low to mid 70s highs. Strong cold front arrives Wednesday afternoon with a chance for showers and and isolated thunderstorm or two.

- Frontal passage brings significantly colder weather on northeast winds Thursday and Friday.

DISCUSSION

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

Offshore high pressure continues our southwest winds and above normal temperatures. Dry weather expected today, although there will be enough mid and high clouds around to limit sunshine at times. It will also be rather breezy, especially near the coast as a 40-60 kt low level jet develops. This jet is above a low level inversion, which will prevent these stronger winds from mixing down efficiently, especially over the coastal waters. Soundings still showed a shallow mixed layer supportive of 25-35 mph gusts over land.

Expecting minimum relative humidity to be higher today. In collaboration with MA fire weather partners, will continue the Special Weather Statement to raise awareness of some drier fuels due to a lack of recent rainfall.

KEY MESSAGE 2...Increasing risk for rainfall tonight into Tuesday. Above normal temperatures continue.

A backdoor front will push south from northern New England and may reach the northern MA border by Tuesday morning. Continued SW flow and advection of higher dewpoint air into our region will result in areas of stratus developing, and can't rule out patchy drizzle overnight along with a few showers as higher humidity moves in. Cloud cover and SW flow will keep low temperatures tonight right around our normal high temperatures for late March.

This front lingers into Tuesday, keeping most of our region within the warm sector of a low pressure moving into the Great Lakes. Considerable cloudiness for all areas though, but weaker forcing (better to our north and west). A modest increase in humidity with drier air aloft probably favors very light rain or drizzle. Cannot completely dismiss the idea of an isolated thunderstorm or two creeping past the Berkshires from NY state during the afternoon. Well above normal temperatures continue.

KEY MESSAGE 3...Period of above normal temperatures peaks on Wednesday, with a chance for lower to mid 70s highs. Strong cold front arrives Wednesday afternoon with a chance for showers and and isolated thunderstorm or two.

Still looking like quite a warm day Wednesday although recent guidance has honed in on the chance for slightly cooler conditions (widespread 60s instead of 70s). Still, with 925mb temps as high as +15C, the potential exists for highs in the mid 70s in some of the usually warmer spots (CT and Merrimack Valleys). Most locations likely warm into 60s/low 70s 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 4...Frontal passage brings significantly colder weather on northeast winds Thursday and Friday.

Heights build to >570dm late week as an upper level ridge builds across the eastern CONUS. We won't feel the impacts from these building heights at the surface, however, as the late week/early weekend still appears cooler, overcast and raw. Increasing NE winds pushes a shallow layer of cold air south across the area. 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 strong inversion will maintain low clouds with intermittent showers and likely lead to a pretty raw day on Thurs. NBM temps in the mid 40s to lower 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.

Another period of strengthening northeast winds likely brings a reinforcing shot cooler temps Saturday. May see some relief from the cooler conditions ahead of a frontal system Sunday, but that may come at the cost of some showers.

AVIATION /06Z MONDAY THROUGH FRIDAY/

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

Today...High Confidence.

VFR. Fairly light winds this morning become SW and increasing to 10-15 kt with gusts to 25-30 kt this afternoon. Areas of LLWS this afternoon over the Cape/Islands with a strengthening low level jet.

Tonight...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.

Tuesday...Moderate Confidence.

MVFR-IFR with scattered rainfall. Some improvement to VFR possible from south to north during the afternoon. Low risk for TSRA along and west of the CT River during the afternoon.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt. Chance RA.

Wednesday: Mainly VFR, with areas MVFR possible. Windy with areas of gusts up to 30 kt. Chance RA.

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

Thursday through Thursday Night: MVFR/IFR conditions possible. Breezy. Chance RA.

Friday: Mainly VFR, 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 today. Could see some gusts approach gale force across the waters south and east of Nantucket, as well as the outer RI coastal waters, but think a Small Craft Advisory is more appropriate. Winds and seas briefly subside tonight into Tuesday, but still expecting rough seas across the southern coastal waters. Extended the Small Craft Advisory into Wednesday where confidence is highest.

Outlook /Tuesday Night through Friday/...

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

Wednesday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 12 ft. Chance of rain.

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

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 this evening for ANZ230- 236. Small Craft Advisory until 11 PM EDT this evening for ANZ231- 250-251. Small Craft Advisory until 2 AM EDT Tuesday for ANZ232>234. Small Craft Advisory until 7 PM EDT Wednesday for ANZ235-237- 254>256.