textproduct: Boston / Norton

WHAT HAS CHANGED

Extended the time of the Small Craft Advisory to Monday evening. Otherwise, no significant changes to the forecast.

KEY MESSAGES

- Unsettled weather continues this weekend as slow low pressure slowly moves away into the Gulf of Maine.

- More clouds than sun for early to midweek, with seasonable temperatures.

- Turning unsettled late this week potentially into part of the weekend.

DISCUSSION

KEY MESSAGE 1...Unsettled weather continues this weekend as slow low pressure slowly moves away into the Gulf of Maine.

Current surface analysis shows that a weak area of low pressure has developed just SE of the islands early this afternoon. This feature will hold the most sway over the weekend's weather as it slowly deepens and moves NE into the Gulf of Maine over the next day or so. Aloft, a potent upper level low will provide enough instability for showers and low clouds providing for a generally raw and unsettled weekend.

For today, expect periods of showers to redevelop this afternoon after a lull this morning. Shower activity will be driven by a rather potent mid level low. This low should pass overhead tonight. The colder air aloft will result in increased lapse rates, which in turn should increase shower coverage later today and tonight. These showers will be much lighter in intensity. The greatest coverage of showers should be towards northern and eastern MA.

For Sunday, expect similarly raw and unsettled conditions as cyclonic flow results in a final round of wrap around showers. Greatest chance for additional appreciable rainfall exists across northern Massachusetts. Any lingering rainfall comes to an end by mid morning Sunday as a much drier air mass wraps in behind departing low pressure. Partial clearing by the afternoon helps to mix the boundary layer allowing for a breezy day with NW winds increasing to between 10 and 15 mph with gusts 20-30 mph.

Temperatures both days increase into the lower to mid 50s with lows falling into the upper 30s to low 40s.

KEY MESSAGE 2...More clouds than sun for early to midweek, with seasonable temperatures.

Southern New England looks to be on the periphery of an active WNWly northern stream flow per ensembles and AI-based solutions through midweek, to go along with cooler profiles aloft (e.g. 850 mb temps around 0 to -2C). While generally dry weather looks to prevail, cooler profiles aloft should support more of a mix of clouds and sun. Highs should run mainly in the upper 40s interior/higher terrain to the mid 50s in the lower elevations, which are around seasonable for this time of year. KEY MESSAGE 3...Turning unsettled late this week potentially into part of the weekend.

Model ensembles and AI-based guidance continue to point to the latter part of the upcoming workweek into a part of next weekend as becoming increasingly active, although there is still quite a bit of uncertainties in the details. This more active period of weather appears to stem from a rather potent northern stream trough coming out of the Canadian Prairie region potentially phasing with trough energy coming out of the central Rockies occurring around midweek. This stream-phasing is indicated more bullishly by the GFS/ECMWF ensemble means, which show a resulting deep closed low at 500 mb near the central Appalachians, and sfc offshore low pressure development near the mid-Atlc states which returns northward or northeastward near or east of the 40N/70W benchmark area around Friday night and continuing into Saturday. The Canadian GEM is more of an outlier, which shows cool but dry weather Fri-Sat as the two streams never phase, instead bringing a coastal low pressure in around Saturday night and/or Sunday.

Given the above, and that is is still effectively a Day-6 to Day-7 forecast, there's still too much uncertainty at this point in time to really drill into the details. Generally speaking, pronounced easterly onshore flow would tend to favor coastal areas and potentially further inland staying as a cool, raw rain given SSTs which are still in the mid 50s. However there appears to be sufficient enough cold air aloft particularly in interior portions of Southern New England that could force a cool-rain-to-wet-snow scenario into the picture, and this is reflected in some ensemble members and in some AI-ensembles. But those are really just big picture pattern-recognition assessments, and we'll need to continue to monitor subsequent guidance for more agreement in terms of the sfc low track, its timing and how far east would sub-0C air aloft extend.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

Today...High confidence.

Many areas may remain IFR through the afternoon and evening based on the latest guidance. NW and WNW winds continue this afternoon into the evening, and generally remain at or below 10 kt.

Tonight...Moderate confidence.

IFR/MVFR ceilings in scattered rain showers overnight. West winds start light and increase through the overnight hours; 10-15 kts with gusts to 20 kt, except for 20-30 kt gusts for Cape and Island terminals. A more solid area of rain moves into the eastern terminals including BOS between 08-09z. Steady rain lingers through at least 12z Sun.

Sunday...High confidence.

MVFR and local IFR conditions improve to VFR by afternoon from SW to NE. MVFR conditions take longer to clear out for the Cape and Islands. W winds increase to 10-15 kt with gusts as high as 30 kt by the afternoon.

KBOS Terminal...High confidence in trends, moderate confidence in exact timing and exact details.

KBDL Terminal...High confidence in trends, moderate confidence in timing and exact details.

Outlook /Sunday Night through Thursday/...

Monday: Mainly VFR, with local MVFR possible. Breezy. Slight chance RA.

Monday Night through Tuesday Night: VFR. Breezy.

Veterans Day: VFR.

Wednesday Night: Mainly VFR, with local IFR possible.

Thursday: VFR. Slight chance RA.

MARINE

Forecaster Confidence Levels...

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

Through Sunday...High confidence on trends, lower confidence on exact timing and details.

Gusty W to NW winds develop tonight into Sunday, which will lead to another round of rough seas, mainly across the outer coastal waters. While there will likely be several hours of a lull in Small Craft Advisory conditions, may just extend it across the outer RI coastal waters for messaging. Rough seas and gusty winds should return by this evening there. Elsewhere, Small Craft Advisory conditions develop tonight and continue through at least Monday night.

Outlook /Sunday Night through Thursday/...

Monday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Chance of rain.

Monday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Tuesday Night: Winds less than 25 kt. Areas of rough seas.

Veterans Day: Winds less than 25 kt. Areas of seas approaching 5 ft.

Wednesday Night: Winds less than 25 kt.

Thursday: Winds less than 25 kt. Slight chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 4 AM to 1 PM EST Sunday for ANZ231. Small Craft Advisory from 10 PM this evening to 7 PM EST Sunday for ANZ232-233. Small Craft Advisory from 1 AM to 1 PM EST Sunday for ANZ234. Small Craft Advisory from 7 PM this evening to 7 PM EST Sunday for ANZ235-237. Small Craft Advisory from 4 AM to 7 PM EST Sunday for ANZ250. Small Craft Advisory from 7 AM to 1 PM EST Sunday for ANZ251. Small Craft Advisory from 10 PM this evening to 7 PM EST Monday for ANZ254. Small Craft Advisory from 7 PM this evening to 7 PM EST Monday for ANZ255. Small Craft Advisory until 7 PM EST Monday for ANZ256.