textproduct: Boston / Norton

WHAT HAS CHANGED

Increased probabilities for gale-force gusts in the Monday-Wednesday timeframe.

KEY MESSAGES

- Lingering showers this morning towards the southern coast, Cape Cod, and the Islands. Otherwise, drier and colder today.

- Dry with a modest warmup through mid next week, but monitoring stormy conditions near or south of the mid-Atlantic waters which could bring periods of light rain, enhanced northeast winds, and building waves/possible erosion to southeast New England.

DISCUSSION

KEY MESSAGE 1...Lingering showers this morning towards the southern coast, Cape Cod, and the Islands. Otherwise, drier and colder today.

Showers over much of SE MA and RI continue this morning with the cold front associated with a low pressure system now over New Brunswick, Canada draped over the southern portion of the south shore down into coastal RI. This front will continue eastward early this morning, and we will find ourselves in a much colder and drier airmass with high pressure starting to build in from the west. These showers should remain generally over SE MA, Cape Cod, the Islands, and parts of RI this morning, then drop off more towards the afternoon as the drier air behind this front really sets in. Skies will clear more towards the evening, especially with high pressure taking more of a hold overhead by then. Gusty NW winds today as strong cold air advection develops and the gradient between the exiting low pressure to our northeast and the high pressure to our west tightens, which may reach up to 35 mph in some areas this afternoon. 925 mb temperatures fall below 0C by this evening, and prior to that mark, they look to hover just above it. Highs today will likely struggle to reach the low 50s across the interior and lows Saturday night will likely dip below freezing across the region, with the exceptions being areas closest to the coasts and urban areas. Once the gusty NW winds diminish later this evening, we could see some radiational cooling develop as high pressure builds in post-FROPA, enhancing an already relatively cold night for some locations. Areas of frost/freezing conditions are anticipated, though because our program came to an end on October 11, there will be no Frost/Freeze headlines issued.

KEY MESSAGE 2...Dry with a modest warmup through mid next week, but monitoring stormy conditions near or south of the mid- Atlantic waters which could bring periods of light rain, enhanced northeast winds, and building waves/possible erosion to southeast New England.

High pressure continues to build in Sunday and the colder airmass shifts out of the region. The tighter gradient between the strong exiting low and approaching high pressure slackens, which will allow winds to continue diminishing as well. As high pressure settles in overhead, temperatures will moderate back to more typical levels for this time of year as 850 mb temperatures improve from -5C today to around +5C by Sunday evening. 925 mb temperatures steadily increase as well, reaching around +10C towards the Monday/Tuesday timeframe. Highs return to the 50s and 60s into early next week.

One thing we will be keeping an eye on, though, is the development of low pressure towards the mid-Atlantic/Carolina coastal waters Sunday into Monday. This feature appears to have detached from the broader upper level trough that was associated with the strong low pressure that brought yesterday's precipitation. Guidance is indicating that a weaker spot in the surface ridge over southern New England may allow for some showers to sneak in sometime Monday/Tuesday over southeastern New England. Given the dry conditions preceding these possible showers, QPF looks quite limited, with ensemble probabilities for any measurable rainfall mostly between 10-50%, with the GEFS and Canadian ENS skewing slightly higher over the Cape and Islands at 50-60%. The ECMWF ensemble is the lowest of the three, with the highest probabilities over land being 10-30%. However, marine impacts with this disturbance are looking a bit more impactful as it stays relatively stationary and churns over the same waters for an extended period of time, which will help build seas up to 15 ft offshore of Nantucket. The gradient between this area of low pressure and the preexisting high pressure over southern New England will tighten greatly, increasing ENE winds over the waters and towards the Cape and Islands, RI, and the coastal plain in SE MA. Ensembles have continued to indicate decent probabilities of sustained winds reaching gale-force over the southern waters, with the GEFS and Canadian ensemble up to 30-40% (and even up to 60% in the Canadian guidance) just south of the Islands. In terms of gale- force gusts, probabilities have increased further from the last update, reaching the high (80-100%) range in the ECMWF ensemble and up to 80% in the GEFS. Persistent easterly fetch associated with these winds, along with building rough seas, will need to be monitored as well, as beach erosion for east- and northeast- facing beaches may become an issue.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Today: High confidence in TAF/trends, but moderate on when SHRA clears southeast New England.

VFR, but rain showers could linger until early afternoon for PVD, and potentially into mid afternoon for the Cape and Islands. North and west from there, VFR prevails. Gusty NW winds around 13-17 kt with gusts 25-30 kt.

Tonight: High confidence.

VFR. Easing NW to N winds to around 5-10 kt by midnight, continuing to ease to light NW overnight.

Sunday: High confidence.

VFR. Light N winds, though becoming NE around 8-12 kt for the Cape and Islands.

KBOS Terminal...Moderate confidence in TAF. Timing of showers could be slightly later than the TEMPO, though should not vary too much from those hours.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR.

Monday: VFR. Breezy.

Monday Night: Mainly VFR, with local MVFR possible. Breezy.

Tuesday: VFR. Breezy.

Tuesday Night: VFR. Windy with areas of gusts up to 30 kt.

Wednesday: VFR. Windy with gusts up to 30 kt.

MARINE

Forecaster Confidence Levels...

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

Through Sunday...Moderate confidence.

Gusty NW winds today following an overnight cold front. Uncertainty remains regarding the potential for gale-force wind gusts over the ocean zones for tonight, which currently are forecast to remain just under gale-force. Latest guidance has trended winds aloft tonight to generally in the mid-20 kt range up to the 850 mb mark, which would very much keep winds below gale criteria. Seas remain generally within Small Craft Advisory levels for the coastal and outer waters, though seas build to around 8 ft by Sunday in the ocean zones after the other waters briefly fall back to around 4 ft at most. Winds diminish greatly Sunday, sustained up to 15 kt over the southern waters and up to 10 kt over the eastern/NE waters. Gusts remain generally below 20 kt Sunday.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Rough seas up to 15 ft.

Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 16 ft. Chance of rain showers.

Monday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 15 ft. Chance of rain showers.

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to 12 ft. Chance of rain showers.

Tuesday Night: Strong winds with gusts up to 40 kt. Rough seas up to 12 ft. Slight chance of rain showers.

Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 12 ft. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230- 236. Small Craft Advisory until 2 AM EDT Sunday for ANZ231-251. Small Craft Advisory until 8 AM EDT Sunday for ANZ232>235-237- 250. Small Craft Advisory until 11 AM EDT Sunday for ANZ254>256. Gale Watch from this evening through Sunday morning for ANZ281>283.