textproduct: Boston / Norton

SYNOPSIS

Strong high pressure will continue to provide dry weather through much of this weekend. Decreasing clouds early today in eastern New England, although ocean effect cloud cover will continue across Cape Cod and the Islands through early tonight. Gradual warming temperatures are expected Friday and Saturday. An approaching low pressure will bring the potential for mainly rain late Sunday into Monday, with perhaps a bit of ice at the onset across the interior.

NEAR TERM /UNTIL 6 PM THIS EVENING/

645 AM Update:

Overall no major change with this intermediate update. Regarding the ocean effect precip, it looks to be becoming more focused along a N to S convergence zone, inferred from NE winds at Provincetown and NW winds near the Mass Bay buoy. Still don't think expected accumulations are enough to warrant any change in messaging, with SPS in effect for slippery road conditions in eastern Plymouth and (western) Barnstable Counties. NAM-3km suggests this band could linger until close to 15z. Meanwhile OVC conditions continue over much of central and eastern MA, eastern CT and RI; the coverage is decreasing rapidly across south- central NH. These trends all captured well in going forecast so no changes needed.

Previous discussion from earlier this morning:

Little change on the synoptic scale with strong, broad high pressure centered near Montreal QC extending ridging through Southern New England. That being said, shallow maritime moisture has allowed for an overcast layer of stratus to blanket much of eastern into portions of central MA on into RI, where temperatures were holding steady in the mid 20s to around 30 degrees. This includes a layer of ocean effect stratus which continues across the Cape and Islands, and current radar was also showing intermittent bands of ocean-enhanced precipitation in portions of South Shore and the bay side of Cape Cod. Although temps here are cold enough for snow, patchy freezing drizzle was mixing in with the intermittent snow in these showery bands of precipitation. Meanwhile...travel westward into western MA and the CT Valley and temps have bottomed out into the mid teens to as low as the single digits, with calm winds and clear skies.

Regarding the ocean effect precip bands...I've opted to hoist a special weather statement to address areas of potentially icy roads, which includes the Route 3 corridor and into the Cape over the Sagamore Bridge on Route 6. The moist layer is so shallow that both light snow and freezing drizzle are the two only outcomes, and have also made mention of that in the weather grids too. The bands have been fairly intermittent too, and while Marshfield was reporting visbys down to 2 SM at times, I don't think accumulations will be much worse than greasy coatings. NAM-3km suggests this activity ceases around 9 AM, so wanted to bring some awareness that roads could be slippery in spots for commuters/post-holiday shoppers.

Otherwise the main forecast challenge is timing the dissipation of stratus in eastern MA and RI. Full sun is expected in northern CT and much of western and central MA today. Expect the ongoing stratus layer to gradually peel away, starting soonest on the northern and western periphery of it into the North Shore and central/northwest RI by sunrise, and then through Boston/Providence around mid morning. By afternoon, most areas should trend mostly clear except over the Outer Cape and Islands where it will take until after sundown before clearing occurs. For temperatures today...we actually begin a warming trend with 850 mb temps climbing to around +2 to +3C, but shallow mixing is expected per BUFKIT fcst soundings such that we won't be able to mix to these low- level temps. Instead, offered values in the mid 30s to near 40 for today.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/

345 AM Update:

Tonight:

The strong high pressure then begins to settle southward into Southern New England, with anomalously strong upper level ridging to boot. Although there may be just enough NW wind over the Outer Cape to keep lows in the mid to upper 20s, the remainder of Southern New England is expected to see nearly optimal radiational cooling conditions. I ended up using MOS guidance for lows tonight given these conditions, which supports lows in the teens for most, with single digit to perhaps readings near zero over far northwest MA.

Friday:

High pressure south of Long Island will shift winds toward a light SWly direction. This will also continue the warming trend aloft, although mixing still looks too shallow to mix down the +4 to +5C air at 850 mb. Full sun and dry weather are expected, but for temps, I opted to mix from about 925 mb with values here around 0C. Most areas should reach into the upper 30s, although a few lower 40s are possible.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Key Messages

* Mild temperatures expected through the middle of next week

* Trending toward unsettled weather by Sunday with more clouds than sun and multiple opportunities for precipitation

* Low risk for freezing rain across the interior Saturday night into Sunday morning

Saturday and Sunday

A large area of high pressure moves off the coast of The Carolinas Friday night through Saturday. This will support a pattern change characterized by mild temperatures, cloudiness, and multiple opportunities for precipitation. Saturday will feature increasing cloudiness and temperatures in the 40s as southerly flow advects moisture and milder temperatures over southern New England. There is a low chance for some warm advection driven showers on Saturday, but otherwise expecting cloudy but dry conditions. Forcing for ascent looks to strengthen Saturday night into Sunday as pulses of short- wave energy begin to traverse over the region. This should support periods of steady light precipitation Saturday night into Sunday. With a very warm column, we wouldn't expect any snowfall, however, surface temps near freezing over the elevated areas of interior MA may be at risk for a freezing rain event. This will depend on timing as the milder air mass in place will only support sub-freezing temperatures for a few hours Saturday night/early Sunday morning over portions of The Berkshires and Worcester Hills. The Canadian Ensemble (GEPS) is more bullish for freezing rain with greater than a 50% chance of at least a glazing by Sunday morning. The GEFS on the other hand only supports a 10 to 20 percent chance. As mentioned previously, this will depend heavily on timing, so we'll be monitoring that aspect of the forecast closely this weekend as higher resolution model guidance becomes available.

Next Week

After a steady round of warm frontal precipitation on Sunday, a more substantial round of rainfall will be in the cards Sunday night into Monday as a wave of low-pressure moves over The Northeast. This will be followed by a lull (likely on Tuesday), before another wave of short-wave energy deepening over the southeast may bring a coastal storm to southern New England by the middle of next week. Given the mild antecedent conditions leading up to the middle of next week, we wouldn't expect this system to be of the Nor'Easter/snow storm variety, but we'll see how the forecast shakes out as we get into next week. For now, there is moderate confidence in mild/unsettled weather through at least next Wednesday. Stay tuned for further details....

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecast Confidence Levels:

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

12z TAF Update:

Today: High confidence.

BKN/OVC stratus at most airports this morning with bases 030-035, although BDL and BAF are SKC VFR. Expect stratus to decrease in coverage to VFR from NW to SE; it will take until tonight before ocean effect clouds over the Cape and Islands become VFR. NW winds 5-8 kt today then become more light WNW late in the day.

Tonight: High confidence.

Any leftover MVFR bases out over the Cape and Islands should trend to VFR early. Should be VFR for the remaining airports. It's currently viewed as low-prob with no mention in the TAFs, but there are some signals for patchy radiation fog tonight in eastern New England. Light WNW to W winds.

Friday: High confidence.

VFR. Light W/WNW winds become SW around 5 kt by 13 to 15z.

KBOS TAF...High confidence in TAF. BKN/OVC VFR bases, 035 should be common but could slip briefly to 030 thru 13z. Decreasing cloud coverage will be the trend. NW winds 5-8 kt becomes WNW around 5 kt or less by 22z, which continues into tonight.

KBDL TAF...High confidence in TAF. VFR today and tonight with light N winds.

Outlook /Friday Night through Monday/...

Friday Night: VFR.

Saturday: Mainly VFR, with local IFR possible. Chance RA.

Saturday Night through Sunday: MVFR/IFR conditions possible. RA likely.

Sunday Night through Monday: Mainly MVFR, with areas IFR possible. Breezy. RA.

MARINE

Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.

350 AM Update:

Opted to issue a lower-end SCA for leftover 5 ft seas for the waters east and south of Cape Cod through tonight. Early morning buoy obs at Jeffrey's Ledge were running around 4 ft, although buoy 44011 near Georges Bank was nearly 9 ft. Expect continued 5 footers through today in those far southeastern waters, with seas elsewhere running 4 ft or less.

NNW winds today around 10-15 kt to steadily decrease and shift to light W tonight and then become SW around 5-10 kt on Friday.

Mainly dry weather is expected, although there could be patchy freezing drizzle through mid morning today for vessels traveling through Cape Cod Bay, Mass Bay and east of Cape Cod.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt.

Saturday: Winds less than 25 kt. Chance of rain.

Saturday Night through Sunday: Winds less than 25 kt. Rain likely.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain likely.

Monday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 8 ft. Rain likely.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ254-255.