textproduct: Boston / Norton

WHAT HAS CHANGED

Temperatures were increased today with highs reaching the upper 40s to the middle 50s expected. A strong cold front may bring a few snow showers and perhaps even a localized snow squall Thursday into Thursday evening with the greatest risk for that across interior southern New England. Winds increased later Thursday into Friday with Gale Watches issued for all our waters. This will result in wind chills by daybreak Friday between 5 below and 5 above zero and perhaps near 10 below in the highest terrain. Some of the overnight guidance especially the AI versions have increased potential for some mixed precipitation and/or snow over the weekend...but confidence remains low.

KEY MESSAGES

- Unseasonably mild today with highs in the upper 40s to the middle 50s with a few rain showers possible tonight.

- Colder air begins to work into the region Thu with falling temperatures and perhaps a few rain/snow showers and even a localized snow squall.

- Windy & very cold Thu night-Fri. Wind chills between 5 below and 5 above and near 10 below in the highest terrain Fri morning.

- Uncertainty remains whether we will see some mixed precipitation and/or snow this weekend. There have been some westward trends in some of the overnight guidance...but need to see if this continues over the next 24-48 hours.

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

DISCUSSION

KEY MESSAGE 1...Unseasonably mild today with highs in the upper 40s to the middle 50s with a few rain showers possible tonight.

Strong shortwave will dig and deepen over the Great Lakes this afternoon. Guidance shows heights falling to around 510dm as the shortwave moves E. Ample southwesterly WAA ahead of the feature allows for a very unseasonably mild day. High temps today will likely overachieve given the mild start and reach the upper 40s to the middle 50s

Column will take a while to saturate through the day with a rather stubborn layer of dry air between 5-10 kft modeled on BUFKIT soundings. This means that shower activity will likely hold off until this evening into the overnight. Column will start off quite warm for mid January so expecting precipitation to start as rain tonight. Will see a strong cold front make its way through the CWA by daybreak Thursday, it's possible that some light snow could expand as far east as the Worcester Hills. Little snow accumulation is expected.

KEY MESSAGE 2...Colder air begins to work into the region Thu with falling temperatures and perhaps a few rain/snow showers and even a localized snow squall.

Strong cold front sweeps through the region early Thursday morning trailing behind deepening low pressure as it pulls away into northern New England. Strong CAA leads to non diurnal temperature trends Thurs with temps starting in the upper 30s in the terrain and lower to mid 40s elsewhere. High res guidance shows temps falling through the 30s and perhaps mid to upper 20s by 00z Friday. Will feel even colder thanks to winds gusting 20-25 mph late in the day as the pressure gradient tightens between the deepening low and the incoming ridge of high pressure. CAA continues into early Friday with 925mb temps dropping to -15C before rebounding as heights rise toward the weekend. This means one night (Thursday night) of lows in the single digits and low teens. Friday, highs only reach into the 20s with continued breezy winds.

Finally, we will have to watch for the chance of snow showers/squalls late Thursday morning into the afternoon especially for western Mass. Boundary layer may be mild enough for even a few rain showers initially towards the I-95 corridor. High res guidance is somewhat split with the NAM 3km showing more moisture and even some low CAPE values. The HRRR is less enthused due to drier air working in on west flow. Regardless, the threat will need to be monitored as lapse rates steepen and ample forcing arrives via the Arctic front later Thursday afternoon.

KEY MESSAGE 3...Windy & very cold Thu night-Fri. Wind chills between 5 below and 5 above and near 10 below in the highest terrain Fri morning.

Low pressure rapidly intensifies as it lifts northeast into the Canadian Maritimes. This result in a brief shot of very cold air with 850T dropping to between -18C/-19C by daybreak Fri. We may see a lingering spot snow shower or two Thu night...but the main story will be a brief shot of very cold air.

Winds will likely overachieve given the magnitude of the CAA and expect westerly wind gusts of 25 to 45 mph. This will result in low temperatures by daybreak in the teens with perhaps some high single digit readings in highest terrain. This coupled with the windy conditions will result in Wind Chills between 5 below and 5 above early Fri morning and perhaps near 10 below zero across the highest terrain. It remains windy and cold on Fri with high temperatures only in the upper 20s and lower 30s across most locations.

KEY MESSAGE 4...Uncertainty remains whether we will see some mixed precipitation and/or snow this weekend. There have been some westward trends in some of the overnight guidance...but need to see if this continues over the next 24-48 hours.

There remains considerable uncertainty on the track/timing and strength of a potential offshore/coastal low pressure system this weekend. The long range guidance continues to struggle with the potential outcomes given several pieces of northern stream energy along with differences in their timing/strength and amplitude. This will ultimately help to determine where/when offshore low pressure develops as well as its strength.

We have seen some of the 00z guidance track trend a bit back towards the coast this weekend. This is particularly true with the 00z UK/ICON guidance as well as the GEFS AI version. Meanwhile...the operational GFS/ECMWF/CMC are still basically a very small glancing blow/miss. Their individual ensemble members still lean that way...but there are a few that support a track closer to the coast than yesterday. Model trends over the next 24 to 48 hours will be key...but something will need to watch.

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

Regardless of what happens this weekend...long range ensembles are in very good agreement on upper level ridging across western north America with a trough across the eastern CONUS. This should result in very cold/below normal temperatures for the first half of the next work week.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Today...High Confidence.

VFR despite mid level cloudiness. S-SW winds 5 to 15 knots.

Tonight...Moderate confidence.

Mainly VFR into at least the first half of the evening. Widespread 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 Thu morning improve to mainly VFR during the afternoon. However...a few brief spot rain/snow showers possible and perhaps 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.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR. Windy with gusts up to 35 kt. Slight chance SHSN.

Friday: VFR. Windy with gusts up to 35 kt.

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

Saturday: VFR. Breezy. Chance RA, chance SN.

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

Sunday: VFR. Breezy. Chance SN.

MARINE

Forecaster Confidence Levels...

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

Today through Thursday...High Confidence.

Southwest wind gusts of 20 to 30 knots early this morning gradually diminish later today and tonight as core of LLJ departs. Seas will also temporarily diminish...but marginal 5 foot seas may 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.

Outlook /Thursday Night through Sunday/...

Thursday Night: Moderate risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Freezing spray, slight chance of snow showers.

Friday: Moderate risk for gale force winds with gusts up to 40 kt. Seas up to 5 ft. Freezing spray.

Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas.

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

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of rain, chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Gale Watch from late Thursday night through Friday afternoon for ANZ230-236. Small Craft Advisory until 1 PM EST this afternoon for ANZ231>235-237-250-251. Gale Watch from Thursday evening through Friday afternoon for ANZ231>235-237-250-251-254>256. Small Craft Advisory until 7 AM EST Thursday for ANZ254>256.