textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes since the previous forecast update. A Winter Weather Advisory remains in effect for the threat of freezing rain across portions of southern New England through this morning. Most locations along the I-95 corridor will experience a light glace of ice, though locations across interior southern New England may see an additional ice accumulation of 0.1". Plan on slick travel this morning.

KEY MESSAGES

- Freezing rain creates hazardous road conditions this morning for much of southern New England. Improvements by late morning to early afternoon, quieter conditions tonight to Thursday.

- Pattern change brings in milder temperatures late week with periods of rain through the weekend. Gusty west winds late Sunday into Monday.

DISCUSSION

KEY MESSAGE 1...Freezing rain creates hazardous road conditions this morning for much of southern New England. Improvements by late morning to early afternoon, quieter conditions tonight to Thursday.

Ongoing freezing rain across portions of the area this morning is creating hazardous travel conditions on untreated surfaces. A Winter Weather Advisory in effect through 10 AM for northern Rhode Island, northern Connecticut, and much of Massachusetts away from southeast sections, including Cape Cod and the Islands.

A low pressure system over the eastern Great Lakes continues to move east-northeast across central and northern New England. Ahead and east of the low, a mid-level warm front brought an initial band of precipitation Tuesday evening, with a surface warm front arriving a few hours later. This has allowed surface temperatures to rise above freezing across the coastal plain, temporarily ending the freezing rain threat. Interior and high-elecvation locations remain more susceptible, where cold air is still entrenched near the surface and freezing rain continues. Model guidance continues to show a weak secondary area of low pressure developing as the primary low exits. This will induce a rapid shift in winds to the northwest to north- northwest, allowing colder air to drain southward. As a result, marginally warm surface temperatures may fall from the middle 30s into the lower 30s, bringing a renewed threat for freezing rain and possibly some snow showers on the back edge of the system as it wraps up and exits late this morning. Any lingering precipitation tappers off between 10 AM and 1 PM, with the remainder of the afternoon remaining cloudy and temperatures holding in the middle 30s.

Cold air advection for Wednesday night into Thursday morning, with drying conditions and northwest winds around 10 mph. Overnight lows fall below freezing, allowing any untreated wet surfaces to refreeze. By Thursday, increasing mid-level heights and high pressure build east from the Mid-Atlantic coast to the waters south of southern New England. Warm air advection supports milder a milder airmass, with afternoon highs in the middle 40s under partly to mostly clear skies.

KEY MESSAGE 2...Pattern change brings in milder temperatures late week with periods of rain through the weekend. Gusty west winds late Sunday into Monday.

There is good agreement among ensemble guidance for a pattern change later in the week favoring a period of milder temperatures and generally unsettled weather. A subtropical ridge builds in from the south into Friday accompanied by warming temperatures aloft. This will support above normal temperatures rising into the 40s to near 50 during the day Friday. The northern stream pattern trends active Friday into the weekend with a series of shortwave troughs with a weak wave tracking to the north across the Great Lakes Fri-Sat followed by a deeper trough pushing across the northeast with a secondary low development. With ample moisture, this will support a few rounds of rain Friday through the weekend.

SW flow aloft will help advect in above normal moisture into the region, around 250-300 percent of normal. This is certainly in the upper percentiles of climo. Ensembles show a more likely range of 0.50 to 1" of rain, although there are some individual solutions that indicate potential for locally higher amounts. Something to keep an eye on for trends in future guidance. For timing, the first round of rain moves through Friday afternoon/Friday night. The second "wave" will be more robust/synoptically supported bringing in a period of steadier rainfall Saturday into Sunday.

Relatively cooler air moves behind the system bringing seasonable temperatures Sunday into early next week. Gusty westerly winds are looking more likely later Sunday into Monday with an enhanced pressure gradient and some cold advection post cold-front. Ensemble guidance shows moderate probabilities (50-60%) for gusts greater than 40 mph for the east Berkshires and 30-50% probabilities for the Worcester Hills and Cape/Islands.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

06z TAF update...

Through 12z... Moderate Confidence.

Low cigs/vsbys becoming widespread IFR-LIFR as RA and FZRA overspreads the region. Mostly FZRA interior with brief snow possible at onset north of Route 2. Otherwise, rain near the coast. Light N-NE wind becoming E near the coast.

Today... Moderate Confidence.

IFR-LIFR conditions persist in the morning with gradual improvement to MVFR-VFR through the afternoon away from the coast. Areas of FZRA or FZDZ in the interior may expand toward the E-NE MA coast during the morning. Winds shifting to N-NW during the morning increasing mid-late afternoon.

Tonight... High Confidence.

Mainly VFR, although MVFR may linger into the evening for Cape/Islands. NW wind 5-15 kt.

Thursday... High Confidence.

Dry. VFR. Light NW wind becomes W, less than 8 knots. Wind may become calm after 21z with high-pressure moving into the region.

KBOS Terminal... Moderate Confidence.

IFR cigs with LIFR cigs/vsbys developing late into Wed morning. Rain develops after 02z but could begin as a brief period of FZRA before temps climb above freezing. Winds shift back to N-NW Wed morning and that may lead to some -FZRA/-FZDZ as colder air is drawn southward.

KBDL Terminal... Moderate Confidence.

Conditions lowering to IFR tonight with pockets of LIFR. Areas of FZRA develop after 00z transitioning to -RA/-DZ late tonight as temps climb above freezing.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR.

Friday: Mainly VFR, with local MVFR possible. Breezy. Chance RA, slight chance FZRA.

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

Saturday: MVFR/IFR conditions possible. Breezy. RA likely.

Saturday Night: Mainly MVFR, with areas IFR possible. Breezy. RA.

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

MARINE

Forecaster Confidence Levels...

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

Key Point:

- Small Craft Advisory in effect today & Wednesday for the southern waters and eastern outer waters for seas greater than 5 feet.

Today through Thursday... High Confidence.

Low-pressure system moves east of the Gulf of Maine with increasing winds from the W, gusts between 20 to 30 knots. Occasional mixed wintry precipitation tapper off from southwest to northeast during the late morning into the early afternoon. Seas across the southern waters increasing 4' to 8', eastern waters 3' to 6'.

An area of high-pressure exits off the Mid Atlantic Coast on Thursday morning, settling over the southern waters. Seas and winds diminish, falling below advisory criteria.

Outlook /Thursday Night through Sunday/...

Thursday Night: Winds less than 25 kt.

Friday through Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of rain.

Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Rain likely.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Winter Weather Advisory until 10 AM EST this morning for CTZ002>004. MA...Winter Weather Advisory until 10 AM EST this morning for MAZ002>017-026. RI...Winter Weather Advisory until 10 AM EST this morning for RIZ001>004. MARINE...Small Craft Advisory from 1 PM this afternoon to 1 AM EST Thursday for ANZ235-237. Small Craft Advisory from 1 PM this afternoon to 7 AM EST Thursday for ANZ250. Small Craft Advisory from 1 PM this afternoon to 1 PM EST Thursday for ANZ254. Small Craft Advisory from 7 AM this morning to 1 PM EST Thursday for ANZ255-256.