textproduct: Boston / Norton

WHAT HAS CHANGED

Added a chance of showers on Monday with an approaching upper level disturbance. Otherwise, no significant changes to the forecast.

KEY MESSAGES

- Drier and cooler this afternoon and overnight as deepening low pressure continues to move away.

- Cloudy and unsettled start to the workweek as multiple weak disturbances move through.

- Monitoring potential storminess late this week into part of the weekend, with lower elevation rain and higher elevation rain mixing with wet snow possible.

- Cloudy, cool, and blustery weather for late weekend into early next week.

DISCUSSION

KEY MESSAGE 1... Drier and cooler this afternoon and overnight as deepening low pressure continues to move away.

Visible satellite shows pockets of stratocumulus clouds indicative of ongoing strong low and mid level cold air advection this afternoon. Another indicator is the stiff west breeze that will continue this afternoon as mixing heights rise to >3 kft and tap into a 35-40 kt LLJ. Model soundings show a well-mixed PBL overnight and so expect lows to remain a bit warmer than they otherwise could be. Lows tonight likely remain above freezing, ranging from the mid 30s inland to the low to mid 40s across coastal areas. Greatest chance of better decoupling and cooler temperatures will be found across interior valleys where lows may dip into the lower 30s early Monday morning.

KEY MESSAGE 2...Cloudy and unsettled start to the workweek as multiple weak disturbances move through.

We remain under WNW flow with another upper level trough clearing the region through Monday night, and with it cooler temperatures prevail aloft. 850 mb temperatures look to fall below 0C late Monday night then steadily improve through the day on Tuesday to around 2- 4C. These cooler conditions aloft will remain supportive of a mix of clouds and sunshine. Guidance has trended towards more in the way of isolated to scattered showers Monday afternoon as low level lapse rates steepen to 8-9 C/km. Best forcing for ascent will be found across NW Massachusetts so expecting scattered coverage of showers there and isolated coverage elsewhere. Highs Monday and Tuesday look to be generally in the 40s and 50s with lows in the 30s. These more seasonable temperatures are expected to continue through at least midweek as the WNW to W flow aloft continues. Breezy conditions at the surface are expected at least for Tuesday as another low looks to pass to our northeast.

KEY MESSAGE 3...Monitoring potential storminess late this week into part of the weekend, with lower elevation rain and higher elevation rain mixing with wet snow possible.

Model-ensembles and AI-based guidance continue to point to potential late-week / early-weekend storminess. However these models continue to vary on the placement, strength and eventual exit of the modeled surface low; as well as the thermal structure and more specifically, the extent to which sub-freezing air aloft can penetrate into Southern New England. A lead shortwave disturbance coming out of the north-central Rockies Tue moves into the central Plains around early Wed; then the 500 mb CONUS pattern amplifies substantially as strong Pacific trough energy induces amplifying upper ridging across the Rockies by midweek. Strong northerly 500 mb flow then helps allow for additional pieces of shortwave energy coming out of the northern Canadian Prairies/northern Canada to dig southward and/or potentially phase with the Rockies trough around Thursday/Thursday night. It's a complicated interaction and how those pieces come together are critical in terms of resolving the above described uncertainties. The net result is a deep upper trough/closed low at 500 mb located somewhere in the OH/TN Valleys; and an organizing surface low moving northward from the mid-Atlantic states Thursday night, and over or in vicinity of Southern New England around Friday, with lingering influence possibly into the upcoming weekend.

Latest guidance indicates that sub-freezing air aloft could struggle to make it into Southern New England at least initially, only then slowly bleeding into interior higher terrain areas in Southern New England late Friday night and/or into Saturday, possibly facilitating a rain to a gloppy wet snow changeover in the higher terrain. Lower elevations and the coastal plain seem more favored to stay as primarily rain due to both above-freezing air aloft and the influx of "milder" onshore flow of maritime air (SSTs still in the mid 50s). The GFS-based guidance has shown a westward/inland trend over the past few cycles which is a warmer and wetter outcome. The international guidance is closer to the 40N/70W benchmark or even further east, which would bring colder air in sooner but would in turn also be more removed from the best moisture/modeled QPF. Highest ensemble probabilities for an inch or more of snow at a 10:1 SLR across the interior higher terrain are still in the moderate range at around 40-60% and are less than 20% for snow totals of 3 or more inches.

Still is time to reassess the guidance, and continued variation in the guidance is likely over the coming days, at least until the lead shortwave becomes better resolved as it comes out of the Rockies around Tuesday.

KEY MESSAGE 4...Cloudy, cool, and blustery weather for late weekend into early next week.

Depending on exactly when the late week/early weekend cyclone pulls away, we'll be left in a cool cyclonic flow aloft. Expect considerable cloudiness and cool temperatures, to go along with blustery northerly winds into early next week.&&

AVIATION /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

Tonight...High confidence.

VFR. SW to WSW winds generally 5-10 kt. Winds towards the Cape and Islands may be slightly higher. Cloud cover increases after midnight with ceilings starting to decline over western MA.

Monday...High confidence.

VFR for most. Local MVFR possible across the higher terrain of central and western MA. Mainly dry, but perhaps a few showers towards western MA. Breezy once more starting in the late morning hours for most, gusting to 20-25 kt, especially for the higher elevations. Winds W becoming more NW through the afternoon.

Monday Night...High confidence.

VFR. Localized high-end MVFR possible towards the higher elevations in western MA. WNW-NW winds 5-10 kt, slightly breezier for the Cape and Islands.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday through Veterans Day: VFR. Breezy.

Wednesday Night: VFR.

Thursday: VFR. Breezy. Chance RA.

Thursday Night: VFR. Windy with areas of gusts up to 30 kt. RA likely.

Friday: Mainly VFR, with local IFR possible. Windy with gusts up to 35 kt. RA likely, SN likely.

MARINE

Forecaster Confidence Levels...

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

Through Monday...High confidence.

Lingering rough seas, mainly across the southern outer coastal waters. The rough seas across those waters are likely to persist through at least Monday night, and perhaps longer. SCA conditions likely in these areas.

Outlook /Tuesday through Friday/...

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

Veterans Day: Winds less than 25 kt. Seas up to 5 ft.

Wednesday Night: Winds less than 25 kt.

Thursday: Winds less than 25 kt. Chance of rain.

Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Chance of rain, slight chance of thunderstorms.

Friday: Strong winds with gusts up to 40 kt. Rough seas up to 12 ft. Rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ232- 233-235-237-250. Small Craft Advisory until 7 PM EST Tuesday for ANZ254>256.