textproduct: Boston / Norton

WHAT HAS CHANGED

Brief snow showers or possible snow squalls developing late this afternoon to early tonight, best chance for interior Southern New England but still possible for eastern MA and RI. Gusty to strong winds then develop tonight and peak overnight to early Monday before easing. Still monitoring a possible coastal storm system late in the upcoming workweek but uncertainty remains large on its strength and track.

KEY MESSAGES

- Cold front brings risk for brief snow showers and possible snow squalls late this afternoon to early tonight.

- Turning windy and much colder tonight into early Monday morning.

- Conditions turn unsettled by Wednesday with periodic showers. Continuing to monitor a potential coastal system towards the end of the week.

DISCUSSION

KEY MESSAGE 1...Cold front brings risk for brief snow showers and possible snow squalls late this afternoon to early tonight.

We continue to monitor the progress of a cold front, now working its way through central NY from roughly Syracuse to Binghamton. A broken line of heavy snow showers and snow squalls was marking the location of this front. While this seems to be well handled by short-term model forecasts, it seems to be moving about a couple hours earlier than those model forecasts would indicate. Although temperatures have been warm enough for initial plain rain, rapid surface temperature cooling in the minutes after its arrival has allowed for a changeover to brief heavy snow with visbys as low as one-half mile. Simple extrapolation puts the cold front and this band of precipitation into the Berkshires/I-91 corridor between 3 and 5 PM, and into central MA, eastern CT and western RI between 4 and 7 PM. Somewhat higher confidence in these locations having a better chance at experiencing brief (< 60 min duration) snow showers which could reduce visibility substantially and slicken roads in its short duration. Based on model forecasts it's less certain if this band maintains itself into the Boston to Providence I-95 corridor and east/southward - if it were to, it would likely be in the 6 to 8 PM timeframe. Reminder that snow squalls are primarily a transportion hazard, but since there could be a higher volume of traffic on main and secondary roads/interstates than a typical Sunday afternoon to early evening, we wanted to give this threat a little more visibility. May consider snow squall warnings which are products geared for motorists if visibilities were to drop to white-out conditions, which are at least possible.

KEY MESSAGE 2...Turning windy and much colder tonight into early Monday morning.

Passage of the cold front this evening will be marked by steadily falling temperatures into the mid 20s and increasing WNW wind gusts with rapid drying likely as well as sharp cold advection develops. NWly wind gusts in the 35 to 45 mph range develop later tonight and peaking into the overnight to early Monday morning hours, with gusts up to 50 mph in the Berkshires. The Wind Advisory was maintained for the Berkshires, but felt gusts were too borderline elsewhere to warrant any spatial expansions. Given the strong winds and falling dewpoint temperatures, that should be enough to permit good evaporation/drying of wet pavement so the risk of black ice should be on the low side.

Easing WNW winds are expected Monday morning, although still a rather breezy day, with winds eventually turning WSW as an approaching weak wave of low pressure passing to our north brings some midlevel clouds for Mon aftn.

KEY MESSAGE 3...Conditions turn unsettled by Wednesday with periodic showers. Continuing to monitor a potential coastal system towards the end of the week.

Tuesday looks to remain primarily dry with warmer temperatures in the low 40s. By Tuesday night/Wednesday morning, a weak shortwave pushes through and may bring a few scattered showers. Uncertainty remains high on if the showers will remain as all rain or mix in a few snow flurries. Regardless, DESI probabilities of accumulation >0.01" remain less than 30 percent across southern New England.

Expecting the pattern to become more amplified as we head towards the end of the week, with colder temperatures making a return by Thursday night/Friday morning. We're continuing to monitor the potential for a coastal low to form Thursday into Friday in the mid- Atlantic or just offshore. Confidence remains low on the potential impacts at this time as deterministic and ensemble guidance (both model to model and run to run) remain quite spread in possible tracks and timing. Ensembles indicate the low moving across anywhere from northwest MA, southeast MA, or completely offshore. Will continue to monitor trends as the details become more clear in the guidance.

AVIATION /06Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

TAF Update: 06z

Through 12z... High confidence.

VFR. Gusty to strong WNW winds 15-25 kt, gusts 30-40 kt, on the higher end of that range around the western higher terrain.

Today and Tonight... High confidence.

VFR. Gusty NW winds 15-25 kt with gusts 30-40 kt thru mid-morning, then a gradual easing of winds/gusts through the late morning as a layer of mid-level clouds comes in. Late in the day, winds become WSW around 10 kt which continue into the evening/overnight.

Tuesday... High confidence.

VFR, dry, with increasing mid-level clouds during the afternoon. SW winds 10-12 knots, coastal sites have occasional gusts to 18 knots.

KBOS Terminal... High confidence.

Gusty to strong WNW winds, gusts up to 35 knots into midday, before easing this afternoon.

KBDL Terminal... High confidence.

Gusty to strong WNW winds, gusts 30-35 kt into late morning, before easing midday.

Outlook /Tuesday through Friday/...

Tuesday: VFR.

Tuesday Night: VFR. Breezy. Slight chance RA.

Wednesday: Mainly VFR, with local MVFR possible. Breezy. Chance RA.

Wednesday Night: Mainly VFR, with local IFR possible. Chance RA.

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

Thursday Night: VFR. Windy with local gusts up to 30 kt. Chance SN, chance RA.

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

MARINE

Forecaster Confidence Levels...

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

Today through Tuesday... High confidence.

Gale Warnings in effect this evening on all waters. Initial westerly winds around 10 kt shift to WNW upon cold frontal passage and become gusty, with gusts 35 to 40 kt. Seas 7-12 ft on the outer waters with 3-5ft seas nearshore as the NW winds develop. Will need to downshift gale warnings to small craft advisories as winds begin to ease into early Monday morning, with winds becoming WSW around 15-20 kt by late in the day, and continuing into Monday evening.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Slight chance of rain.

Wednesday Night through Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain.

Thursday Night: Strong winds with gusts up to 35 kt. Local rough seas. Chance of rain, chance of snow. Local visibility 1 to 3 nm.

Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Wind Advisory until 9 AM EST Monday for MAZ002-008-009. RI...None. MARINE...Gale Warning until 7 AM EST Monday for ANZ230>237-251. Gale Warning until 10 AM EST Monday for ANZ250-254>256.