textproduct: Boston / Norton

WHAT HAS CHANGED

Winter Weather Advisories issued for Essex, Middlesex, and Suffolk Counties for 3-4 inches snow possible tonight. Winter Weather Advisory issued for Hartford and western Hampden County for a glaze of ice possible tonight.

KEY MESSAGES

- A fast-moving clipper will bring a period of accumulating light snow starting late this afternoon through late tonight.

- Quiet pattern overall with periods of nuisance light snow and minimal impacts. Temperatures moderate to near seasonable norms. Attention turns to the late weekend for a potential coastal storm, but forecast confidence remains low due track uncertainty.

DISCUSSION

KEY MESSAGE 1...A fast-moving clipper will bring a period of accumulating light snow starting late this afternoon through late tonight.

A mid-level shortwave trough is expected to move into New England Tuesday night with the surface low tracking well to our north. A SW- NE LLJ accompanies the system helping advect in a plume of above normal moisture(150-200% of normal). Broad ascent ahead of the warm front and advancing LLJ will support a period of snow later today and tonight. Snow/flurries arrive late this afternoon to this evening from west to east with the most consistent showers in MA, especially north. Majority of model and ensemble guidance agrees on a light accumulation event 0.5" to 3". There will be a few things at play that could favor periods of moderate snowfall rates. Model guidance has identified warm frontogenetical forcing somewhere in east/northeast MA this evening. In addition, the advancing LLJ from the southwest will bring stronger ascent as it pushes closer late tonight. Model soundings show sufficient lift within the dendritic growth zone this evening and tonight, showing a favorable environment for more enhanced snow rates. As a result, bands with moderate snow rates are possible with the highest chances for MA with the most consistent banding positioned over northeast MA. For timing, this evening through late tonight is the more likely timeframe to see periods of moderate snow before dry air works in aloft. Precipitation exits the region early Wednesday morning.

HREF probabilities reflect this with 50-70% probabilities across Essex County for 3" snow or greater, but lower probs for greater than 4". Additional counties show potential for closer to 3" inches in surrounding counties such as Middlesex County. All this means is these favored areas for enhanced snowfall, we could see locally up to 4 or 5, mainly in northeast MA. Winter Weather Advisories have been issued in those areas.

Have kept an eye on the secondary low development offshore of the Cape. Its associated inverted trough is more likely favored to impact areas further north (Maine) based on the low position/track. This lowers the risk for another mesoscale forcer to bring enhanced snowfall in our region.

With a warm nose pushing in from the south, a wintry mix or change to rain is possible late tonight/early Wed AM, especially along the immediate south coast and Cape/Islands. Model soundings indicate potential for a change over to freezing rain in Hartford County and in the Berkshires late tonight. This would likely be a brief period, but potentially enough to bring a glaze of ice. As a result we issued a Winter Weather Advisory for those areas for the light glaze of ice possible. Towards the end of the event (after midnight), the upper/mid-levels dry fairly quickly leaving it saturated at the lower levels. Patchy freezing drizzle may be possible for the full column dries out Wednesday morning. Model soundings have been borderline with showing this potential lowering confidence/coverage of the drizzle. Snow amounts will be limited as a result further south (less than 2").

KEY MESSAGE 2...- Quiet pattern overall with periods of nuisance light snow and minimal impacts. Temperatures moderate to near seasonable norms. Attention turns to the late weekend for a potential coastal storm, but forecast confidence remains low due track uncertainty.

Wednesday through Saturday feature generally benign weather. A surface low exits east of the coastal waters on Wednesday as high pressure builds across the Midwest. While the pressure gradient is modest, it will support northwest wind gusts of 20-30 mph Wednesday afternoon. High temperatures remain seasonable in the mid to upper 30s, though wind chills will fall into the 20s. As the surface low departs Wednesday night, a subtle inverted trough extending westward may produce a few snow showers, mainly across Cape Ann and areas southward to outer Cape Cod into early Thursday morning. Moisture is limited and forcing is not well aligned with the dendritic growth zone, limiting snowfall to a light coating at most.

Otherwise, surface high pressure builds across the eastern CONUS through the end of the week, maintaining seasonable temperatures. An upper-level low and northern-stream shortwave cross New England Friday night into early Saturday, bringing a low (<30%) probability of snow showers. This remains a moisture-starved system with PWATs below climatological normals, though minor accumulations are possible across the higher terrain of northern and western Massachusetts.

Looking ahead, guidance continues to signal the potential for a coastal storm late this weekend into early next week. Predictability remains low at this range. Most 18z/00z deterministic guidance (GFS, ECMWF, CMC, and AI guidance) favors a track well offshore and no impacts to southern New England. The UKMET remains an outlier with a closer solution near the benchmark. At this time, confidence in any impacts remains low, though the system bears monitoring.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Through 12Z...High confidence.

VFR. NW winds 5-10 kts. Mid-level cloud decks in central and western southern New England.

Today...Moderate confidence.

VFR and dry to start. VFR cloud bases as light snow moves in during the afternoon from west to east (19-21Z arrival in western MA and 23-00Z arrival at BOS). Ceilings drop to MVFR around or after 00Z. Light NW winds in the morning trend toward the SW after 15Z.

Tonight...Moderate confidence.

IFR/LIFR in snow, moderate at times possible especially across northern MA, including KBOS. Steadiest snow roughly 00z-05z. Snow may end as rain along the south coast. Can't rule out patchy -FZDZ after the bulk of precipitation has ended; however, this is low confidence.

Wednesday...High confidence in trends.

Improving ceilings through the morning. NW winds gusts up 20-25 kts.

KBOS Terminal...Moderate Confidence. -SN arrives more likely between 23-00Z. Ceilings should trend downward as steadier snow develops after 00Z. Period of moderate snow tonight between 00-06Z. This would bring briefly lower visibilities (1/2SM) and IFR/LIFR ceilings. Snow moves out by 09Z.

KBDL Terminal...Moderate Confidence.

Outlook /Wednesday through Saturday/...

Wednesday through Friday: VFR. Breezy.

Friday Night: VFR. Breezy. Slight chance SN.

Saturday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Tuesday through Wednesday Night...High Confidence.

Seas continue to subside this morning, with wave heights of 2-4 ft. Southwest winds remain 10-15 kt with occasional gusts up to 20-22 kt. A surface low moves across northern into central New England tonight, then emerges offshore of southern New England Wednesday morning. In the wake of this system, southwest winds increase and veer to the west-northwest at 15-20 kt with gusts up to 30 kt on Wednesday. Seas build to 4-7 ft on the southern outer waters and 3-6 ft on the eastern outer waters. Small Craft Advisories will likely be needed mid-morning Wednesday through Wednesday night.

Outlook /Wednesday through Saturday/...

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft.

Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of snow.

Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Freezing spray.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

Friday Night through Saturday: Winds less than 25 kt. Slight chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Winter Weather Advisory from 6 PM this evening to 6 AM EST Wednesday for CTZ002. MA...Winter Weather Advisory from 6 PM this evening to 6 AM EST Wednesday for MAZ005>007-009-014-015-026. RI...None. MARINE...Small Craft Advisory until 7 AM EST this morning for ANZ250- 254>256.