textproduct: Boston / Norton

WHAT HAS CHANGED

Gale watches issued for our open waters Thursday night through Friday night. Mainly a widespread cold rain expected later Thursday into Friday...but some minor wet snow accumulations are possible too mainly in the high terrain.

KEY MESSAGES

- A few showers possible across the interior near daybreak Thu. Otherwise...a widespread cold rain focused late Thu into Fri. Rain may flip to or mix with wet snow with the greatest risk for that in the high terrain. Any snow accumulations look minor at this time.

- Cool with mainly dry conditions Saturday through early next week.

DISCUSSION

KEY MESSAGE 1...A few showers possible across the interior near daybreak Thu. Otherwise...a widespread cold rain focused later Thu into Fri. Rain may flip to or mix with wet snow with the greatest risk for that in the high terrain. Any snow accumulations look minor at this time.

Low pressure across the north central plains will shift eastward tonight and emerge off the mid-Atlantic coast Thu. This low will intensifies as it tracks near or inside the Benchmark into Friday. We will break things down in much greater detail below.

As the surface low moves east tonight...mid/high level cloudiness will begin to overspread the region. As the system approaches the mid-Atlantic a S-SE low level jet will develop near daybreak across the interior. This may result in some lower clouds along with a few showers developing at this time as well. As this low pressure system emerges off the coast...a modest E low level jet will develop during the day Thursday. However...model soundings indicate that there is a lot of dry low level air hanging around along the coastal plain...so much of Thu may end up dry/cloudy with just a few spot showers. Therefore...bulk of showers on Thu likely confined to the interior for much of the day and amounts on the lighter side.

The steady/widespread rain will overspread the region Thu after 4-5 pm into the evening hours as deeper forcing/moisture arrives. This will be a result of the surface low pressure intensifying as it passes near or just inside the Benchmark into Fri. Therefore...expect a cold rain for much of the region Thu night into Fri. The question then becomes do thermal profiles become cold enough for the rain to flip to a period of wet snow. Thermal profiles are very marginal and the exact track of the mid level centers along with precipitation intensity will determine if this happens. Right now the greatest potential for this is across the interior high terrain...mainly the east slopes of the Berks/Worcester Hills. However...some of the guidance especially the REFS indicate a track further south. This actually brings the greater risk of wet snow further south into the CT/RI Hills. In fact...there is even a low risk for rain to briefly mix/change with wet snow even right the I-95 corridor. We should have a better idea on this potential in the next 24 hours...but regardless any impacts will likely be rather limited at this point. A coating to 2" of slushy wet snow is a possibility in the high terrain with a low risk of 3". Greatest risk for this would be at elevations near or above 800 feet and particularly near 1500 feet. Of course this will be dependent on the track of the 700 mb low pressure system and if precipitation rates can be heavy enough.

The other story on Friday will be the unseasonably cold temperatures. Given N low level flow along with clouds and precipitation...daytime temperatures will generally be in the 30s to the lower 40s! Bulk of the precipitation should wind down later Fri...but a few left over showers can not be ruled out near the coast Fri night.

KEY MESSAGE 2...Cool with mainly dry conditions Saturday through early next week.

The surface low pressure system slowly shifts further eastward into the Atlantic Saturday. The bulk of the precipitation will have exited with the low. While it will likely be dry in most areas, residual moisture flow may support some isolated/"pop-up" showers. A below normal airmass will be positioned across the region supporting highs in the mid to upper 40s with the higher terrain areas in the upper 30s to low 40s. Breezy NW winds make temperatures feel more like the mid 30s to low 40s. Expect a chilly night Saturday night with temperatures falling into the 20s and 30s. High pressure slowly builds in from the west Sunday into early next week bringing a period of dry conditions. Another breezy cool day Sunday with winds decreasing by Monday as the pressure gradient relaxes. Temperatures slowly moderate closer to seasonable values Tue/Wed.

AVIATION /19Z WEDNESDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Wednesday evening and overnight...High confidence.

VFR and dry conditions. NW Winds 10-15 kts late Wed afternoon diminish and becoming northerly overnight.

Thursday...High confidence.

VFR to start, lowering to MVFR after 18Z with -RA overspreading the region. IFR possible at ORH after 18z. NE winds 10-15 kts, then gusting 20-25 kts at times after 18z.

KBOS Terminal...High confidence in TAF through 18z, then some uncertainty on exacting timing arrival of MVFR and rain in the afternoon.

KBDL Terminal...High confidence in TAF through 18z, then some uncertainty on exacting timing arrival of MVFR and rain in the afternoon.

Outlook /Saturday through Monday/...

Saturday: Mainly VFR, with local IFR possible. Breezy. Slight chance RA.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.

Sunday: VFR. Breezy.

Sunday Night through Monday: VFR.

MARINE

Forecaster Confidence Levels...

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

Tonight through Friday night...

* Gale Watch for the open waters Thu night through Friday night

The main forecast concern is low pressure which will emerge off the mid-Atlantic coast. In response...the pressure gradient will increase and have hoisted Gale Watches for our open waters Thu night through Fri night for the potential of N-NE wind gusts up to 35 knots. Seas will also become quite rough. Have also hoisted small craft advisories for Boston Harbor/Narragansett Bay during this time.

Outlook /Saturday through Monday/...

Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 8 ft. Chance of rain.

Saturday Night: Winds less than 25 kt. Rough seas up to 8 ft. Chance of rain.

Sunday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain.

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 6 PM Thursday to 7 PM EST Friday for ANZ230-236. Gale Watch from late Thursday night through Friday evening for ANZ231>235-237-255-256-282-283. Gale Watch from Thursday evening through Friday evening for ANZ250-251-254-280-281.