textproduct: Boston / Norton

WHAT HAS CHANGED

Temperatures have trended warmer with a slower cold front today. Highs may reach the upper 40s for most of the region with perhaps a few 50 degree readings in the I-95 corridor. This has reduced the threat for daytime snow squalls but there is still a chance for rain or even graupel showers during the afternoon. A dusting to 2" of snow possible very late Friday night into Saturday mainly northwest of I-95. There is the potential for a plowable snowfall across parts of the region Sunday into Sunday night night if coastal low pressure tracks close enough to the coast...but that remains uncertain. High confidence in a shot of arctic air later Monday into Wednesday with bitterly cold wind chills possible.

KEY MESSAGES

- Unseasonably mild today with a few rain and elevation snow showers possible. Turning windy and much colder tonight and Friday.

- A dusting to 2" of snow possible very late Fri night into Sat with temps rising above freezing outside the highest terrain by afternoon. Bulk of the snow likely northwest of I-95.

- Coastal storm may bring a plowable snow to parts of the region Sun into Sun night if it tracks close enough to the coast...but that remains uncertain.

- Shot of arctic air follows later Mon into Wed with bitterly cold wind chills and highs temps held between 15 and 25 Tue into Wed. Wind Chills below zero with moderate freezing spray/gale force wind gusts across our waters.

DISCUSSION

KEY MESSAGE 1...Unseasonably mild today with a few rain and elevation snow showers possible. Turning windy and much colder tonight and Friday.

Unseasonably mild today with high temps generally between 45 and 50...but the big story will be much colder and windy weather working into the region tonight and Friday.

Winds ramp up behind the front with an increasing pressure gradient as low pressure deepens to the north. Northwest winds at 850mb increase to 40 to 50 kts as low level lapse rates increase to 7.5-9 C/km. This will translate to a gusty day with wind gusts steadily increasing through the afternoon and overnight peaking around 30-40 mph. Mid level temperature change will be somewhat dramatic through the afternoon with 850 mb temps falling from +1C this morning to -14C tonight. Lows Friday morning will be 15 to 20F colder than the night previous, in the teens. However, the bigger story will be the frigid wind chill values, in the -5 to +10F range for most location. It will be a brief shot of arctic air, though, with a warmer airmass right behind it.

Generally dry weather prevails today...but a few brief rain showers/elevations snow showers possible. May even see some graupel with instability and cold temps aloft. Strong/cold westerly flow may allow for lake effect moisture to result in a few brief flurries/snow showers tonight with perhaps even a localized snow squall. Overall though the main story will be the much colder temps.

KEY MESSAGE 2...A dusting to 2" of snow possible very late Fri night into Sat with temps rising above freezing outside the highest terrain by afternoon. Bulk of the snow likely northwest of I-95.

A ridge of high pressure off the mid-Atlantic coast moves east and further away from the region Fri night into Sat. In response...shortwave energy lifts northeast across western and northern New England along with a few weak waves of low pressure. In response...a modest southwest LLJ will develop very late Fri night into Sat and over run the cold dome at the surface. The result will be snow developing after midnight and particularly toward daybreak across interior southern New England continuing at times on Sat. A coating to 2" of snow is possible northwest of I-95 which may result in some slippery travel across the interior into Sat morning. However...southerly flow will result in temps rising above freezing across all locations except the highest terrain by Sat afternoon. So while snow may still be in the air Sat afternoon...most treated roadways will just be wet by that time.

The deeper forcing and moisture is focused across the interior...but may see a brief period of light snow near and even southeast of I-95. Regardless...southerly winds will be advecting warmer air into eastern MA/RI with temps rising into the upper 30s and lower 40s Sat afternoon. So really no concerns in this region and any light snow that reaches into this region would change to light rain by afternoon.

KEY MESSAGE 3...Coastal storm may bring a plowable snow to parts of the region Sun into Sun night if it tracks close enough to the coast...but that remains uncertain.

There continues to be a large spread in the track/intensity and timing of coastal low pressure for the latter half of the weekend. The guidance continues to struggle with several pieces of northern stream energy along with their timing and amplitude. This will ultimately determine whether or not phasing can occur with southern stream energy. This would allow upper flow to become more amplified resulting in low pressure system tracking closer to the coast with a more significant impact. Lack of phasing would allow for the low to track further east with a more limited impact. Given this is still a day 4 forecast...all options still remain on the table. The 00z GFS/CMC models continue to have a track closer to the coast potentially bringing a plowable snow to parts of the region. Meanwhile...the 00z ECMWF/UKMET have a track further east with more of a light glancing blow to eastern New England. There also remains quite the spread on the individual ensemble members of each model...showing that we need to keep all options on the table at this point. We did want to point out that the EPS AI ensembles are much closer to the coast with a more significant impact than the regular EPS ensembles. Certainly could be a signal that the EC may correct further west...but again too early to lock in any potential outcomes.

KEY MESSAGE 4...Shot of arctic air follows later Mon into Wed with bitterly cold wind chills and highs temps held between 15 and 25 Tue into Wed. Wind Chills below zero with moderate freezing spray/gale force wind gusts across our waters.

Regardless of what happens Sun into Sun night...long range ensembles are in very good agreement on upper level ridging across western North America with a deep trough across the eastern states for the first half of next week. An arctic cold front crosses the region Mon with bitterly cold air working into the region in the later Mon to Wed time frame. 850T will likely drop into the -20C to -24C for a time. This should result in high temps only in the 15 to 25 degree range Tue and Wed. Lows should drop into the 0 to 10 degree range with perhaps some below zero readings. Wind Chills below zero with moderate freezing spray and gale force wind gusts across our waters.

AVIATION /09Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

06z TAF Update...

Rest of Tonight...Moderate confidence in timing of IFR conditions.

MVFR and IFR conditions continue through the overnight hours. A few showers tonight thru 09z ending from W to E. S winds generally 10 knots or less.

Thursday...High confidence.

Low end MVFR to IFR conditions Thursday morning becoming VFR by the afternoon. Dry on the whole but a few spot rain/snow showers are possible, even a localized snow squall across the interior. SW winds shifting to the W later in the day with gusts increasing to between 20 and 30 knots.

Thursday night...Moderate confidence.

VFR. Gusty W winds continue overnight gusting 20 to 30 kts. A few quick hitting snow showers may impact terminals in the first half of the night, but confidence in placement and timing of these is low.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday through Monday/...

Friday Night: VFR. Breezy. Chance SN.

Saturday: Mainly VFR, with local IFR possible. Chance SN, chance RA.

Saturday Night: VFR.

Sunday: Mainly VFR, with local IFR possible. Chance SN.

Sunday Night: Mainly VFR, with local IFR possible. Breezy. Chance SN.

Martin Luther King Jr Day: VFR. Windy with local gusts up to 30 kt.

MARINE

Forecaster Confidence Levels...

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

Today through Friday...High Confidence.

A strong cold front crosses the region today allowing for winds to pick back up as the day wears along with SW winds shifting more to the W with 25 to 30 knot gusts. Strong CAA will result in W 35-40 knot wind gusts tonight into Friday with light freezing spray. Seas across the southern waters will build to between 6 and 11 feet by early Friday.

Outlook /Friday night through Monday/...

Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

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

Saturday Night: Winds less than 25 kt. Areas of rough seas. Slight chance of rain showers.

Sunday: Winds less than 25 kt. Local rough seas. Chance of rain, chance of snow.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of snow.

Martin Luther King Jr Day: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Gale Warning from 1 AM to 4 PM EST Friday for ANZ230-236. Gale Warning from 7 PM this evening to 4 PM EST Friday for ANZ231>235-237-251. Gale Warning from 7 PM this evening to 10 PM EST Friday for ANZ250-254>256.