textproduct: Boston / Norton

WHAT HAS CHANGED

A few snow squalls possible Thursday. Gale Watches were converted to Gale Warnings for Thursday night into Friday as confidence increases in gusty winds impacting the waters late week. Some guidance continues to show the possibility for a more impactful storm late weekend into Monday. While a high impact storm remains an outlier, we continue to monitor this storm that could bring mixed precipitation and/or snow.

KEY MESSAGES

- Unseasonably mild tonight with a few rain showers.

- Much colder and windy starting Thursday with perhaps a few rain/snow showers and even a localized snow squall.

-Mostly dry Thursday but a few showers or snow squalls are possible.

- Uncertainty remains whether we will see some mixed precipitation and/or snow this weekend.

- Very cold air/below normal temperatures for the first half of the next work week.

DISCUSSION

Key Message 1...Unseasonably mild tonight with a few rain showers.

Continued WAA ahead of a deep mid level trough will mean above average temperatures continue into the overnight hours. Thanks to the warm SW flow lows should only dip into the upper 30s to even low 40s in the urban centers. For reference, the average lows for mid January are in the low 20s. Under this warm advection pattern we'll see the atmosphere saturate over the next several hours as the surface low lifts from western NY into northern New England overnight. Light rain showers overspread late afternoon into the evening, especially over western/central MA and CT with lesser coverage further south and east. The bulk of the precip lifts out by sunrise Thursday.

Key Message 2...Much colder air moves into the region Thursday with falling temperatures and perhaps a rain/snow shower and even a few snow squalls.

Following a sweeping cold front on Thursday temperatures will begin to drop steadily leading to an atypical diurnal trend with temps in the 30s (high terrain) and mid 40s early in the day, dropping into the 20s and low 30s respectively by late afternoon. This, as winds really begin to ramp up after noon as cold advection leads to better mixing while the pressure gradient increases between the deepening low as it exits and an incoming ridge of high pressure. By Thursday evening winds will be gusting 25 to 35 mph for most locations and this continues overnight through much of Friday. Considering 925mb temps drop from +2C Thursday afternoon to -11C Friday morning, we'll see a drastic drop in temps accompanying these winds. 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 +5F range for most locations (as cold as -10F in the Berkshires). It will be a brief shot of arctic air, though, with a warmer airmass right behind it.

Key Message 3...Mostly dry Thursday but a few showers or snow squalls are possible.

When it comes to precipitation, the bulk of the region is dry Thu- Fri. The exception is a chance for some widely scattered snow showers or squalls that are possible during the afternoon and evening on Thursday. The highest likelihood is for western MA/CT in the afternoon, but there is potential that these could spread into eastern MA/RI by late evening. Guidance has continued to hint at this possibility as the likelihood increases of a confluence of steep lapse rates and a strong cold front with lingering low level moisture and gusty winds; the amount of moisture available continues to be the biggest question. While the NAM is the most bullish, other guidance does indicate a quick ramp up of the snow squall parameter and even some weak CAPE as that front moves through. The NAM, GFS, and Canadian models all show 60-80 J/kg of surface based CAPE. accompanying that front.

KEY MESSAGE 4...Uncertainty remains whether we will see some mixed precipitation and/or snow this weekend.

The latest deterministic GFS was along the western edge of the solution envelope, with the Canadian on the eastern edge. All told this provides an error range of nearly 500 miles just between these two sources. The ensembles showed similar uncertainty. Cluster analysis showed the most favored solutions is for a storm track near to just south of our region. Thus, significant uncertainty in the details remains. Kept a mention of the precipitation in the forecast for sometime between Saturday into Sunday night, mainly towards the southeast coast of New England.

With such large differences in the guidance, focusing on a singular deterministic model run is not recommended at this time. We expect to have greater clarity in the outcomes for this weekend over the next 36-48 hours.

KEY MESSAGE 5...Very cold air/below normal temperatures for the first half of the next work week.

Above normal Saturday anticipated to trend to near normal values for Sunday, followed by below normal temperatures by next Tuesday.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

00z TAF Update...

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

VFR first half thru 04z west and 06z then low end MVFR to IFR conditions overspread the region from west to east during the overnight hours. A few showers tonight. 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: VFR. Strong winds with local gusts up to 40 kt.

Friday Night: VFR. Windy with local gusts up to 30 kt. Slight chance SN.

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

Saturday Night: VFR. Chance RA, slight chance SN.

Sunday: VFR. Breezy. Slight chance SN.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SN.

Martin Luther King Jr Day: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

This afternoon through Thursday night...High Confidence.

Seas 2-5 feet persist tonight across the southern outer- waters. A strong cold front crosses the region early Thu 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 gust Thu afternoon and gusting to 35 kt by Thursday night. Seas also increase to 6 to 9 feet on the southern waters Thursday into Thursday night, 4 to 6 feet on the eastern waters.

Outlook /Friday through Monday/...

Friday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 11 ft.

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

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

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 25 kt. Local rough seas. Slight chance of snow.

Martin Luther King Jr Day: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 1 AM to 7 AM EST Friday for ANZ230- 236. Gale Warning from 7 AM to 4 PM EST Friday for ANZ230-236. Small Craft Advisory from 1 PM Thursday to 1 AM EST Friday for ANZ231-251. Gale Warning from 1 AM to 4 PM EST Friday for ANZ231-251. Small Craft Advisory from 7 AM to 7 PM EST Thursday for ANZ232>235-237. Gale Warning from 7 PM Thursday to 4 PM EST Friday for ANZ232>235-237. Small Craft Advisory until 7 PM EST Thursday for ANZ250- 254>256. Gale Warning from 7 PM Thursday to 10 PM EST Friday for ANZ250- 254>256.