textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Mainly dry weather with cooler onshore flow today through the weekend, though some potential for light rain showers along the South Coast on Sunday.

- High pressure with onshore flow continues into midweek, but temperatures start to modify closer to seasonable. Unsettled weather then develops around mid to late next week.

DISCUSSION

KEY MESSAGE 1...Mainly dry weather with cooler onshore flow today through the weekend, though some potential for light rain showers along the South Coast on Sunday.

Southern New England is stuck in a rather blocky midlevel pattern, placed between a broad upper level circulation spiraling around the Canadian Maritimes and far northeastern Maine and an amplified ridge downstream of another closed circulation over the Canadian Rockies. Meanwhile dry surface high pressure continues to ridge southward from Quebec, associated with an extremely dry airmass (PWATs around 0.2 to 0.4"). The circulation to our northeast is associated with an anomalously cool airmass, which will remain with us through the weekend with a period of onshore flow and seabreezes prevailing as well.

Early this morning a pretty extensive canopy of mid-level clouds roughly bisects Southern New England, leading to less clouds and cooler temps east (30s) and comparatively milder west under the cloud deck (40s-low 50s). Radar's showing some echoes here but they're not reaching the ground given dewpoint depressions of 20-25 degrees. This cloud cover should shunt itself southward through the mid morning hours, with full sun anticipated for today. Local seabreezes develop for the coastlines, and the airmass will remain quite dry but winds today will also be quite a bit weaker than yesterday. Highs could struggle to get to the low 50s before the onshore flow develops near the coasts, with full sun and 50s/low 60s inland.

For the weekend...mid level clouds to overspread Southern New England again Saturday as a weak shortwave disturbance coming out of the Gt Lakes links up with subtle trough energy around the NE Canadian upper low. Some of the more coarser-resolution models try to shift some showers into western portions of MA and CT Saturday, but this seems exaggerated; in fact most of the model- derived QPF is more restricted to SW CT/lower Hudson Valley Sat despite there being quite a bit of simulated reflectivity being modeled. Again a reflection of what should be quite a bit of midlevel clouds vs any precip. Onshore flow continues and the canopy of clouds could mean Sat ends up being quite a bit cool in the 40s to lower 50s. Though it's not well agreed upon, there's some indication that as low pressure develops south of Long Island Sunday morning that the surface ridge could weaken enough to allow for some showers to develop into southern RI and remaining sections of the South Coast with some enhanced NE winds; that might be the better chance for any showers but these will be on the light side.

KEY MESSAGE 2...High pressure with onshore flow continues into midweek, but temperatures start to modify closer to seasonable. Unsettled weather then develops around mid to late next week.

Broad Canadian high pressure then reasserts itself back into Southern New England early to mid next week. Dry weather resumes but our low-level temperatures modify, supporting temperatures closer to late- April normals, with continued onshore flow. It looks like the blocky weather pattern begins to break down around mid to late next week, which should bring with it better chances for rain showers, but uncertain at this range when those showers would be more focused after several days of dry weather preceding it.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

12z TAF Update: High confidence.

VFR through the period. For today, northerly winds 5-10 kt, with sea-breezes developing around 14-16z eastern MA coast and south coast 15-17z. Winds then turn E/ENE around 5-10 kt tonight into Saturday, with an increasing canopy of VFR clouds through Saturday.

KBOS Terminal...High confidence in TAF. Winds return to SE seabreezes around 14-15z. Winds then turn ENE early tonight with possible SCT- BKN050 clouds.

KBDL Terminal...High confidence in TAF. VFR, early-day midlevel clouds trend to SKC by mid-morning with N to NE winds.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday Night: VFR. Slight chance SHRA.

Monday through Monday Night: VFR. Breezy. Slight chance SHRA.

Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

High confidence through this weekend.

Winds and seas remain below SCA levels through much of this weekend, east/southeast winds through Saturday around 5-10 kt and seas 4 ft or less. Possible fringe SCA conditions Saturday night into Sunday on southern waters with enhanced NE winds and seas nearing 5 ft as low pressure passes to our south.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday: Winds less than 25 kt. Chance of rain showers.

Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

Monday Night through Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.