textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Sunny with light winds today. Cold again tonight with clear skies and light to calm winds.

- Mainly dry for the upcoming work week, except near coastal areas. Modest warming trend as high pressure builds in over the northeastern US.

DISCUSSION

KEY MESSAGE 1...Sunny with light winds today. Cold again tonight with clear skies and light to calm winds.

High pressure continues overspreading the region today with yesterday's/last night's colder airmass shifting out of the region, along with the upper level trough that's impacted the region over the last few days. With 925 mb temperatures returning closer to 5C and yesterday's cold air advection having come to an end, highs will reach the 50s. Winds also remain light through the day and into tonight with high pressure firmly in place overhead. Skies remain clear through tonight, allowing for another good night of radiational cooling; lows tonight will dip into the 30s and upper 20s.

KEY MESSAGE 2...Mainly dry for the upcoming work week, except near coastal areas. Modest warming trend as high pressure builds in over the northeastern US.

The general trend this week is a drier, somewhat warmer pattern developing as a broad ridge of high pressure settles over much of the northeastern US and into Ontario. Temperatures moderate through the week with highs generally in the 50s and 60s, with cool nights in the 30s and 40s. The only exception to this overall trend is a chance for showers towards the Cape and Islands this week.

A non-tropical low pressure developing along the cold front from Friday night settles just offshore of the Carolina coastal waters. The aforementioned front looks to have stalled out and a bit of upper level energy from the associated trough broke away and drifted to that same area, aiding in the development of this low pressure. Latest HREF members have shown some of the showers associated with the northern precipitation shield of this low making their way up to southeastern parts of New England, mainly the Cape and Islands, finding a weak point in the ridge aloft. Some of the global deterministic guidance agrees, indicating some showers making their way over the Cape and Islands. Though across all models, QPF remains quite low. Latest global guidance (ensemble and deterministic) have also trended down on rain chances later this week. Despite minimal impacts in terms of rain expected with this low pressure, marine impacts are looking a bit more significant as it remains relatively stationary over the same area, churning over the same waters for what appears to be most of this week. This will lead to seas up to 15-17 ft offshore of Nantucket. The gradient between this area of low pressure and the aforementioned high pressure over the northeast US will tighten greatly, increasing ENE winds over the waters and towards the Cape and Islands, RI, and the coastal plain in SE MA. These start to really build up towards Monday night as the low pressure deepens and drifts very slightly north. 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 70% in the Canadian guidance over the ocean waters) just south of the Islands. In terms of gale-force gusts, probabilities have remained somewhat steady compared to the last update, remaining in the high (80-100%) range in the ECMWF ensemble and up to 80% in the GEFS. However, there was a bit of a southward shift of the core of the highest sustained gale probabilities. This lines up with the majority of members across the ensemble suites tracking the center of this low pressure well to the south and east of the 40N/70W benchmark. 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.

Towards the end of the week, ensembles indicate troughing from Canada making a pass towards southern New England, which would aid in steering this low pressure out to sea. Significant ridging aloft over much of the CONUS looks to persist and even intensify, then becomes more tilted towards the Great Lakes region towards the weekend. This would be associated with a strong Canadian high pressure that looks to strengthen over the northeast after originating from the Canadian Prairies, which would lean towards drier conditions for the whole region once again.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

12z Update...

Today...High confidence.

VFR. Calm/light winds continuing through the day today for interior terminals. For eastern terminals, N winds shifting NE after 15Z then to ESE mid-afternoon less than 8 kts. Stronger winds for Cape/Islands between 10-15 kts. VRBL conditions a possibility across interior terminals during the day as high pressure continues aloft.

Tonight...High confidence.

VFR. Southerly winds becoming NW/NNW early Mon AM. Gusts to around 20 kt possible towards the Islands closer to daybreak Monday as well.

Monday...Moderate confidence.

Mostly VFR with the exception of the Cape and Islands towards the late afternoon and evening hours where MVFR ceilings may develop. Chances for -SHRA increase there as well and should remain generally over the Cape and Islands, along with an increased chance for gusts to 25 kt. Winds from the NE and light to calm further inland, 5-10 kt sustained closer to the coasts.

KBOS Terminal...High confidence in TAF. Light NNW winds this AM shifting to the NE after 15/16Z then toward the ESE by mid-afternoon. Speeds 8 kts or less.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

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 through Thursday: VFR. Windy with local 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.

Through Monday...High confidence.

Some marginal lingering small craft advisory conditions may persist across the southern waters through this morning, but will be diminishing. High pressure building in from the west will result in winds/seas falling below small craft today into tonight. 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. Seas start to build up to 15 ft offshore, south of Nantucket and winds gusting to 25 kt in the southern outer waters return by Mon morning, reaching up to 30 kt in the southern ocean zones.

Outlook /Monday Night through Thursday/...

Monday Night: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Chance of rain showers.

Tuesday: Strong winds with gusts up to 40 kt. Rough seas up to 15 ft. Chance of rain showers.

Tuesday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 16 ft. Slight chance of rain showers.

Wednesday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 17 ft. Chance of rain showers.

Wednesday Night: Strong winds with gusts up to 40 kt. Rough seas up to 17 ft. Chance of rain showers.

Thursday: Strong winds with gusts up to 35 kt. Rough seas up to 15 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ232>235-237-250. Small Craft Advisory until 11 AM EDT this morning for ANZ254>256. Gale Watch from Monday evening through Wednesday morning for ANZ254>256-281>283.