textproduct: Boston / Norton

WHAT HAS CHANGED

Winter Weather Advisory for central/western MA is cancelled. The system currently producing some light rain showers in CT/RI, western MA is now forecast to only produce a coating to an inch of snow, with possibly amounts between 2-3 inches in The Berkshires through this evening. Low confidence in advisory thresholds being met, and not expecting any significant impacts. Thus, The advisory has been cancelled.

Wintry mix expected Friday into Saturday with the greatest risk for several inches of snow across northern Massachusetts. Latest guidance favors a graze/miss with powerful coastal storm Sunday night into Monday, but a shift just a bit northwest would bring the potential for heavy snow, strong winds & coastal flooding. All options remain on the table.

KEY MESSAGES

- Light rain/snow showers this evening will be followed by a period of quiet weather with high pressure supporting dry conditions through Thursday night.

- Wintry mix Fri-Fri night with exact snow/ice amounts uncertain. Greatest risk for several inches of snow will be across northern MA. Snow showers linger Sat with additional accumulations possible. - Latest guidance favors a graze/miss with powerful coastal storm Sun night-Mon, but a shift just a bit northwest would bring the potential for heavy snow, strong winds & coastal flooding. All options remain on the table.

DISCUSSION

KEY MESSAGE 1...Light rain/snow showers this evening will be followed by a period of quiet weather with high pressure supporting dry conditions through Thursday night.

A frontal wave and area of low-pressure currently producing some light rain showers in southern New England has progressed far enough south to reduce the overall risk of advisory level snowfall in southern New England. Temperatures across the region currently too warm to support snowfall with surface temperatures ranging from roughly 33-38 degrees. As the afternoon/evening progresses, some cooler air will surge south and is likely to support a period of heavy wet snow showers.

Nonetheless, not expecting any significant accumulations with only a coating to an inch for most locations south and west of Worcester. The Berkshires and higher elevations of western MA/CT are expected to have the most accumulation, but still only around 1-2 inches. The winter weather advisory has been cancelled sinced most locations are no longer expected to reach advisory levels. In addition to the brief period of rain/snow showers, there is also a low risk for a brief period of freezing rain/icing across southeastern MA and southern RI, however the overlap period of rain with sub-freezing temperatures is expected to be very brief so confidence in any icing at the surface is low.

KEY MESSAGE 2...Wintry mix Fri-Fri night with exact snow/ice amounts uncertain. Greatest risk for several inches of snow will be across northern MA. Snow showers linger Sat with additional accumulations possible. The main forecast concern revolves around snow amounts and wintry mix/rain locations Friday afternoon and night across southern New England. Quite a complex forecast as high pressure across Quebec looks to provide enough of a dry/cold antecedent airmass to result in snow and ice across portions of the region. Low pressure then tracks across the Great Lakes with a secondary low pressure system developing off the NJ coast. This is where the forecast becomes quite complex and a race on how quickly the secondary low pressure develops. The reason is that the initial low pressure system will allow mid-level warmth to advect northward across our region...while the secondary low will try to cut that off. So the earlier secondary low pressure develops will result in more snow...while a later development allow for more ice/rain. The NAM/RRFS are the quickest to advance the mid level warmth...while the RGEM/GFS are the slowest. This will make the difference between much of the region receiving several inches of snow or more ice/rain especially southern locations. Even if the warmer mid level solutions verify...shallow cold air may be trapped across parts of the interior resulting in freezing rain.

The forecast remains interesting into Sat as vigorous shortwave energy may result in an inverted trough like feature and periods of snow showers lingering with additional accumulations not out of the question.

So in a nutshell...given the uncertainty we have blended the guidance. The greatest potential for several inches of snow exists across northern MA. This certainly looks like an advisory event...but can not rule out a marginal warning situation across parts of northern MA. This risk would increase if that inverted trough feature sets up and snow showers linger through Sat.

KEY MESSAGE 3...Latest guidance favors a graze/miss with powerful coastal storm Sun night-Mon, but a shift just a bit northwest would bring the potential for heavy snow, strong winds & coastal flooding. All options remain on the table.

The overall theme of the last two main model cycles is more of an offshore track with a potentially very powerful coast storm Sun night into Mon. If this were to come to fruition...we would escape with mainly a graze or even a complete miss. That being said...this is a Day 4-5 forecast which is an eternity in the model world. It would not take much of a shift northwest to bring the potential of heavy snow, strong winds and coastal flooding back into the forecast. Plenty of time here and the model trends will be very important over the next 48 hours. Not much more we can say at this point...but it is way too early to write this one off and it still bears watching.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

Rest of Today and Tonight...Moderate Confidence.

MVFR/IFR celings and visibility with IFR ceilings focused more toward the south coast. Periods of -RA changing over to -RASN later this evening as temperatures fall. Expect significant improvements back to VFR by 06Z as showers taper off. Light northeast winds.

Thurdsay and Thursday night.

High pressure supports VFR conditions through tomorrow night. Winds gradually shift from northeast to southeast during the day tomorrow around 5 knots.

KBOS Terminal...High confidence.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Friday through Monday/...

Friday: MVFR/IFR conditions possible. Breezy. RA, chance SN, chance FZRA.

Friday Night: Mainly IFR, with local VFR possible. Breezy. SN, chance RA, chance FZRA, chance PL.

Saturday: MVFR/IFR conditions possible. Breezy. Chance SN, chance RA.

Saturday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHSN.

Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHSN.

Sunday Night: Mainly VFR, with local IFR possible. Windy with gusts up to 35 kt. Chance SN.

Monday: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt. Chance SN.

MARINE

Forecaster Confidence Levels...

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

High confidence through the end of this week.

Weak low pressure will pass across the southern coastal waters this afternoon and evening. Leftover E swell will maintain 5 ft seas on outer waters where Small Craft Advisories remain posted. Otherwise, relatively light winds and seas expected through Thursday.

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Rain, snow likely, freezing rain. Local visibility 1 to 3 nm.

Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain, snow. Visibility 1 to 3 nm.

Saturday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain, chance of snow.

Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow showers.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft. Slight chance of snow showers.

Sunday Night: Strong winds with gusts up to 45 kt. Rough seas up to 12 ft. Chance of snow.

Monday: gale force winds with gusts up to 40 kt. Rough seas up to 19 ft. Chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 AM EST Thursday for ANZ250. Small Craft Advisory until 7 PM EST Thursday for ANZ254>256.