textproduct: Boston / Norton

WHAT HAS CHANGED

Adjustments to marine headlines - either time extensions and/or conversions from Gale Watches to Gale Warnings - were made. Otherwise no significant changes.

KEY MESSAGES

- Offshore storm brings continued enhanced northerly gusts through Friday morning. Mainly light rain or even light sprinkles are expected overnight tonight into early on Thursday for the immediate southeast New England coastal areas before tapering off Thursday afternoon.

- Prolonged stretch of dry weather Friday into Wednesday. Cooler Friday, followed by moderating temperatures into Monday. Turning cooler toward the middle of next week.

DISCUSSION

KEY MESSAGE 1...Offshore storm brings continued enhanced northerly gusts through Friday morning. Mainly light rain or even light sprinkles are expected overnight tonight into early on Thursday for the immediate southeast New England coastal areas before tapering off Thursday afternoon.

There has been no substantial change to the forecast, messaging and impacts to Southern New England through Friday regarding the distant offshore low pressure slowly meandering northward, located well to the east of the mouth of the Chesapeake Bay as of Wednesday afternoon. This system is mainly bringing some lower-level cloud cover to southeast New England, along with enhanced NE winds with gusts in the 20-25 mph range over most of the mainland, and around 35-45 mph gusts for Cape Cod and the Islands. A rather sharp gradient in cloud cover is noted north and west of I-95, being governed by expansive surface ridging associated with a cooler and drier airmass.

Composite radar mosaic imagery as of Wednesday afternoon is picking up on the western extent of the offshore system's rain shield in our far southeastern ocean waters; latest guidance continues to indicate a continued northwestward creep of this rain shield into the waters near the Islands and eventually spreading toward the south coast and Cape Cod tonight. This rain shield will be fighting dry advection (e.g. dewpoints in the 30s) as it attemps to progress north/west; even across the south coat and the Cape, rain intensities end up being quite light and could struggle to even measure/reach the ground. The best chance at steadiest light rains is across Nantucket and Martha's Vineyard overnight tonight into early Thursday morning. As the distant offshore storm passes toward the northeast on Thursday, expect a decrease in both southeastern New England rain showers and a decrease in cloud cover. Dry weather is anticipated for the remainder of Thursday into Friday as reinforcing surface ridging builds back in from northern Canada.

The main impact for most of Southern New England ends up being enhanced northeast to northerly breezes, strongest for the Cape and Islands in the 35-45 mph range into Thursday noontime, before slowly decreasing into the 20-35 mph range Thursday night into Friday. Seas will continue to build and remain rough, with the greatest impact being for our marine interests.

As has been the case the past couple days, differences in cloud cover and northerly onshore winds has driven a wide range in temperatures. As the coastal low departs, it draws down an increasingly cool airmass in for Thursday night. Clear skies and lighter northerly winds are supporting a larger diurnal range in temperatures across most areas along and northwest of I-95, with chilly nights and milder days with more sunshine. Lows tonight should range in the upper 30s to mid 40s from NW MA to I-95 and in between, with highs in the low to mid 60s on Thursday; with a cold airmass coming in Thursday night, lows are in the 28-34F range for these same areas. Meanwhile toward the southeast coastal areas, a tighter diurnal range in temperatures where cloud cover and northerly winds are the strongest. For these locations, high temperatures end up cooler in the mid to upper 50s are more common, while lows are "milder", in the mid 40s to lower 50s due to the cloud cover and the breezes.

KEY MESSAGE 2...Prolonged stretch of dry weather Friday into Wednesday. Cooler Friday, followed by moderating temperatures into Monday. Turning cooler toward the middle of next week.

Not much change to this portion of the forecast. High pressure dominates our weather into early next week, providing dry weather. Turning cooler Friday with the initial arrival of this high pressure from eastern Canada, followed by moderating temperatures into Monday.

The forecast for Tuesday and Wednesday gets more complex. A front gets sandwiched between the initially discussed high pressure, over the central Appalachians by Monday, and another high pressure over Manitoba and Saskatchewan. This pattern makes it difficult to project the timing and movement of this front, as it will greatly depend on which high pressure is stronger. At this time, thinking the high pressure over Canada will ultimately become the stronger of the two, with the result being this front sweeping across southern New England some time Monday night into into Wednesday. Just how fast this happens, and how far south this front gets pushed, will need to be refined with later forecasts.

There does not appear to be much moisture associated with this front. At this time, the most likely outcome will just be a period clouds and lower temperatures mid week. That said, it would not take much additional moisture to warrant a mention of showers in later forecasts.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

18Z TAF Update:

Through Tonight: High confidence in TAF/trends but moderate on rain shower chances.

VFR with high confidence for TAFs north and west of I-95. For BOS, PVD and the Cape airports, SCT-BKN VFR to MVFR ceilings develop and or persist into tonight. Best chance for most persistent MVFR ceilings and generally VFR-visibility light rain are both restricted to the Cape and Islands.

For the eastern and southeast coast...NE winds around 12-20 kt with gusts 20-35 kt, on the higher end of that range at ACK and lower near the coastal plain. For the interior, northerly winds 5-10 kt.

Thursday: High confidence.

Any VFR-visibility rains end by mid-Thursday morning, with any sub-VFR ceilings over southeast New England TAFs becoming VFR along the same timeframe. Thus VFR should prevail by 15-17z Thursday, although northeast to northerly winds around 10-15 kt with gusts to 25-30 kt should continue along the southeast coast and around 5-10 kt for interior Southern New England.

Thursday Night: High confidence.

VFR. Light northerly winds for the interior, but northerly winds around 10-13 kt for BOS, PVD and Cape and Islands.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Monday/...

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

Friday Night through Saturday: VFR.

Saturday Night through Monday:

MARINE

Forecaster Confidence Levels...

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

Through Friday: High confidence.

Several adjustments to marine headlines were made into Friday, which involved either extensions-in-time of existing SCAs and Gale Warnings and/or conversion of Gale Watches over to Gale Warnings. These changes are being driven by the closest approach of the offshore low pressure as it moves over our far southeast ocean waters Thursday night into Friday.

Gale Warnings over the southern waters were extended until 00z Friday, as ongoing gale force gusts in the 35-40 kt range continue until that point, before decreasing within the small craft advisory range Thursday night into Friday.

For the eastern and southeastern waters (including Cape Cod and the Islands), gale warnings were extended into 18z Friday with gusts in the 35-45 mph range.

For the northeast waters (along and offshore of the mouth of the Merrimack River), SCAs were maintained through early Thursday morning with gusts to around 30 kt, then ramping up into gale conditions with gusts 35-40 kt by Thursday afternoon, which necessitated shifting the Gale Watch into Gale Warnings starting Thursday morning through Friday 18z.

Seas will continue to build and become rough, especially for the eastern and southeastern waters where seas could peak upwards of 16 ft in the outer ocean waters.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Rough seas up to 11 ft.

Saturday: Winds less than 25 kt. Areas of rough seas.

Saturday Night: Winds less than 25 kt. Local rough seas.

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

Sunday Night through Monday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ230. Gale Warning until 2 PM EDT Friday for ANZ231>234-254-255-281- 282. Gale Warning until 8 PM EDT Thursday for ANZ235-237-256-283. Small Craft Advisory until 8 PM EDT Thursday for ANZ236. Small Craft Advisory until 8 AM EDT Thursday for ANZ250-251. Gale Warning from 8 AM Thursday to 2 PM EDT Friday for ANZ250- 251-280.