textproduct: Boston / Norton

WHAT HAS CHANGED

Gale Watches issued for our southern waters early next week.

KEY MESSAGES

- Diminishing winds and clearing tonight with cold low temps in the 20s and 30s with widespread frost/freeze conditions. Sunshine returns on Sunday with highs in the 50s with light winds.

- Mainly dry for the upcoming workweek except near coastal areas. Otherwise, the other big story is a modest warming trend with high pressure building in across the Northeastern United States.

DISCUSSION

KEY MESSAGE 1...Diminishing winds and clearing tonight with cold low temps in the 20s and 30s with widespread frost/freeze conditions. Sunshine returns on Sunday with highs in the 50s with light winds.

Model cross sections indicate that lingering mid level cloudiness pushes south of the region tonight. This combined with high pressure building in from the west coupled with diminishing winds and a dry airmass in place will set the stage for a cold night. Low temps should bottom out in the middle to upper 20s in many locations with lower to middle 30s common in the urban heat islands as well as the Cape/Nantucket where winds will not decouple. Widespread frost/freeze conditions expected...But our Frost/Freeze program has ended already so no headlines needed.

High pressure will result in sunny skies for Sunday. High temps will be in the 50s...which is a bit below normal for this time of year. However...with very little wind outside the Cape/Islands it will feel significantly milder by afternoon than today.

High pressure remains in control of our weather Sunday night with mainly clear skies. This will result in another good night of radiational cooling with lows in the 20s and 30s.

KEY MESSAGE 2...Mainly dry for the upcoming workweek except near coastal areas. Otherwise, the other big story is a modest warming trend with high pressure building in across the Northeastern United States.

General theme for the long term forecast is the return of drier and somewhat warmer conditions going into the workweek as a broad ridge of high pressure develops over the CONUS. Outside of this, guidance continues to indicate the development of low pressure towards the mid-Atlantic/Carolina coastal waters later Sunday into the day on Monday. Ironically, this feature stems from last night's cold front as it continues to move offshore and stall into a stationary boundary. At the same time, lingering upper level energy cuts off and induces the development of a frontal wave off the coast of the Carolinas later Saturday night into Sunday morning. Still see a signal for enough of a weakness in the ridge for low pressure to move N and affect coastal areas Monday and Tuesday. Have continued to see drier solutions with this storm as a dry airmass precedes the northward precip shield. 12z global guidance 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 /18Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

This afternoon through Sunday night...High confidence.

VFR conditions continue through Sunday night. N-NW wind gusts of 20 to 30 knots diminish this evening. Otherwise...calm/light winds overnight into Sunday night except N-NE winds persisting at 5-15 knots across the Cape/Islands.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday: VFR. Breezy.

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

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

Tuesday Night: VFR. Windy with gusts up to 35 kt.

Wednesday: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt.

Wednesday Night: Mainly VFR, with local MVFR possible. Windy with areas of gusts up to 35 kt. Slight chance SHRA.

Thursday: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Tonight through Sunday night...High confidence.

N wind gusts of 20 to 30 knots persist tonight...strongest of which will be across our southern waters. Small craft headlines continue for most of our waters. Some marginal lingering small craft advisory conditions may persist across the southern waters Sun morning. Otherwise...high pressure building in from the west will result in winds/seas below small craft much of Sun into Sun evening. However...distant ocean storm off the mid-Atlantic coast should result in small craft advisory seas/wind gusts returning for our southern waters toward daybreak Mon. Additional marine headlines will be needed for much of the upcoming work week because of this ocean storm.

Outlook /Monday through Thursday/...

Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 14 ft. Chance of rain showers.

Monday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 14 ft. Chance of rain showers.

Tuesday: Strong winds with gusts up to 40 kt. Rough seas up to 14 ft. Chance of rain showers.

Tuesday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 14 ft. Chance of rain showers.

Wednesday through Wednesday Night: Moderate risk for gale force winds with local gusts up to 45 kt. Rough seas up to 15 ft. Chance of rain showers.

Thursday: Strong winds with gusts up to 40 kt. Rough seas up to 14 ft. 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.