textproduct: Boston / Norton

WHAT HAS CHANGED

Small craft advisories now in effect for all waters through Sunday. Best chance for widespread rains is during Sunday afternoon, then a cooldown to temperatures into early next week.

KEY MESSAGES

- Turning overcast with cool onshore breezes and perhaps some drizzle thru midnight, then another round of scattered showers overnight into the pre-dawn hours.

- Still overcast most of Sunday but with modest warming; while generally dry during the morning, widespread rains develop during the afternoon with a cold front, clearing into the waters by evening.

- Rain/snow showers possible Monday night into Tuesday morning, but otherwise dry and cool.

- Temperatures increase through the second half of next week and conditions remain dry.

DISCUSSION

KEY MESSAGE 1...Turning overcast with cool onshore breezes and perhaps some drizzle thru midnight, then another round of scattered showers overnight into the pre-dawn hours.

A backdoor cold front was working its way through central MA and eastern CT, bringing increasing marine cloudiness, much cooler air (40s to low 50s common) and a gusty ENE wind in the 25-35 mph range across eastern MA and RI. This backdoor front will continue to surge westward toward the spine of the Berkshires thru late afternoon. As the PBL continues to cool, expect cloudiness to continue to fill in and lower/thicken as we move into the mid evening hours. There could be some patchy drizzle around as the overcast stratus layer takes hold, but much of the time is dry. Will be rather cool and moist with temps in the mid 30s to low 40s by midnight, with E/ESE winds around 5-10 mph this evening (gusts to 20 mph near the coast).

The lingering frontal boundary then begins to return northward as a warm front overnight, in response to strengthening 925-850 mb warm/moist advection on SWly 40-45 kt LLJ. Rising PWATs and lowering Showalter indices to around 0 units then should allow for a round of scattered showers to develop and move northward sometime thru the 11 pm to 5 am timeframe. Wouldn't rule out a rumble of thunder given falling Showalter indices but this seems like the exception vs the rule. That will also bring with it slowly rising temperatures and dewpoints into the pre-dawn hours, although overcast conditions to continue.

KEY MESSAGE 2...Still overcast most of Sunday but with modest warming; while generally dry during the morning, widespread rains develop during the afternoon with a cold front, clearing into the waters by evening.

We then get into a cloudy warm sector with SW winds around 10 mph (a bit stronger over the Cape and Islands). This cloud cover will be tough to shake free of as shallow moisture remains trapped underneath very mild 925-850 mb temps around +10C. Thus warming would be driven more through advective processes with very little to nil insolational heating. NBM high temps in the upper 50s to mid 60s seem optimistic and brought these down about 5 degrees into the 50s in most areas.

Wouldn't rule out a hit or miss shower during the morning in the cloudy warm sector, but it looks as though the best chance for widespread showers is during Sunday afternoon as a cold front moves in from the west. A round of steady light to at times moderate showers, perhaps with a rumble or two of thunder as Showalter indices dip to -1, as the front gradually trudges east toward the eastern coastal waters by early evening. Additional/lingering rains should persist toward southeast MA, southern RI and the Cape and Islands thru midnight; but the majority of Southern New England to see decreasing cloudiness and falling dewpoints with westerly winds post-frontal. Rain amounts range from about a quarter to third of a inch, perhaps as much as a half-inch in steadier showers. Lows Sunday night in the 30s, with values in the 30-32F range in interior higher terrain as WNW winds pick up.

KEY MESSAGE 3...Rain/snow showers possible Monday night into Tuesday morning, but otherwise dry and cool.

Following Sunday's cold front, colder and drier conditions take hold as surface high pressure starts to take hold and an upper level trough settles overhead. A shortwave may move through the region Monday night into Tuesday morning, which would interrupt this brief dry period with a mix of rain and snow showers. These are not expected to be very impactful to travel or roads as temperatures remain mostly in the 40s and upper 30s. Higher elevations may dip below freezing, but temperatures there will also improve quickly heading into Tuesday morning. Outside of the risk for showers that could linger through the day as the shortwave passes through, drier conditions can be expected as dewpoints fall into the 20s across the region (30s over the Cape and Islands). Tuesday night will be noticeably cooler as the trough sits overhead and 925 mb temperatures fall to -8C to -5C after being just at or below 0C Monday/Monday night. Winds remain mostly W and NW for the start of the week in the post-frontal airmass.

KEY MESSAGE 4...Temperatures increase through the second half of next week and conditions remain dry.

High pressure moves into the Mid-Atlantic region during the second half of the week then shifts more offshore, which will aid in bringing back SW flow over southern New England and keep the region dry. Temperatures will improve as the week goes on and the upper level trough moves off to the east. Highs will likely end up back in the 50s and 60s. Some uncertainty remains, though, towards the end of the week as the GEFS hints at another backdoor front that could lead to cooler temperatures, particularly across eastern MA and RI. If that plays out, highs could struggle to hit 60F Friday afternoon. By comparison, the other ensembles do not have this feature and have highs in the mid to upper 60s. We should get more clarity as we get closer in time.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

00Z TAF Update:

Tonight: High confidence in TAF/trends but moderate on timing any showers.

MVFR lowering to IFR-LIFR stratus and fog after midnight. Scattered showers develop overnight. E wind 10-15 kt with occasional gusts 20-25 kt shifting to SE-S 09-12z.

Sunday: Moderate confidence.

IFR/patchy LIFR early, but should trend toward IFR-MVFR cloud bases by mid-morning to noontime. Possible mist and drizzle ahead of cold front, which brings widespread rain showers approx. 17-23z from west to east. A low chance for a rumble or two of thunder but think SHRA predominates much of the time. SW winds around 10-15 kt (upwards of 20 kt with gusts 25-28 kt Cape and Islands), shifting to W/WNW and decreasing to under 10 kt speeds upon frontal passage.

Sunday Night: High confidence.

Mainly VFR, possible VFR/MVFR ceilings western high terrain. NW winds increase to 10-15 kt with gusts 25 kt.

KBOS Terminal...High confidence in TAF/trends but moderate on timing. E winds around 15-20 kt with area of SCT VFR/MVFR ceilings lingers most of today; deteriorating to MVFR ceilings as soon as 20z, continuing to trend to MVFR-IFR ceilings this evening as winds become ESE. Psbl SHRA 05-10z Sun.

KBDL Terminal...High confidence. VFR with north winds, trending easterly late in the day with arrival of MVFR ceilings. Ceilings continue to lower to MVFR/IFR range early tonight. Psbl SHRA 03-08z Sun.

Outlook /Sunday Night through Thursday/...

Monday: VFR. Windy with local gusts up to 30 kt.

Monday Night: VFR. Chance SN, slight chance RA.

Tuesday: VFR. Breezy. Chance SHRA, chance SHSN.

Tuesday Night: Breezy.

Wednesday through Wednesday Night:

Thursday: Breezy.

MARINE

Forecaster Confidence Levels...

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

High confidence.

Given NE/E gusts are currently in very solid SCA to near-gale- force range with the immediate passage of the backdoor front, and that SWly gusts for Sunday look to be more in the SCA range with strongly- inverted profiles, have hoisted SCAs for all waters starting now through 00z Monday (thus, gale watches on southern waters converted to SCAs).

Expect gusts to be strongest thru Saturday afternoon at around 25-30 kt (occasional gusts to 35 kt possible), then settle in around 25-30 kt range. Seas remain in the 3-5 ft range thru tonight, then increase more markedly as southerly winds increase the fetch, building offshore to nearly 10 ft on southern waters. Winds Sunday night to shift to NW at sub-SCA levels briefly, but could gust to around SCA ranges late overnight Monday.

Low chance at mist/fog overnight, but better chance for rain showers late Sunday afternoon to early Sunday evening.

Outlook /Sunday Night through Thursday/...

Monday: Winds less than 25 kt. Local rough seas.

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

Tuesday: Winds less than 25 kt. Chance of rain showers.

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

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

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

Thursday: Winds less than 25 kt. Seas up to 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Sunday for ANZ230>237-250- 251-254>256.