textproduct: Boston / Norton

WHAT HAS CHANGED

While not set in stone, monitoring a weak area of low pressure Monday or Monday afternoon which could bring cloud cover and possible showers.

KEY MESSAGES

- A few lingering showers are possible tonight. Cooler and mainly dry for Saturday.

- Strong cold front brings a round of widespread showers Sunday. Splashover possible for east coast during early Sunday morning high tide.

- Cooler than normal temperatures for Monday. Although generally dry weather is more likely, monitoring a weak area of low pressure which could bring clouds and scattered showers. Subfreezing low temperatures likely Monday night away from the cities.

- Brief return to seasonable temps on Wednesday, before cooling off again into the latter part of the workweek.

DISCUSSION

KEY MESSAGE 1...A few lingering showers are possible tonight. Cooler and mainly dry for Saturday.

Surface low pressure moves offshore this evening with a few lingering showers possible. For remainder of the night, most places remain dry. Can't rule out a few showers or a sprinkle overnight along the east coast, Cape and Islands overnight with the wrap around moisture from the exited low and onshore flow.

Cooler temperatures expected Saturday with cloudy conditions. 925mb temperatures drop 4-7 degrees from Friday and with cloudy skies should keep temperatures in the 50s and 60s. The warmer range of temperatures is most likely for the CT Valley while the onshore flow will keep temperatures cooler for the on/near the east coast. Easterly winds 5-12 mph.

KEY MESSAGE 2...Strong cold front brings a round of widespread showers Sunday. Splashover possible for east coast during early Sunday morning high tide.

A deep upper level trough shifts across the region Sunday into Monday. Ahead of it, anomalous moisture advects northward into southern New England. A strong cold front will push across the region through the day Sunday supporting widespread rain/showers. A few embedded thunderstorms or downpours are possible given the marginal instability. Not anticipating widespread flash flooding issues, at worst some ponding in poor drainage areas if there is an isolated downpour. As the cold front moves across Sunday late afternoon-evening, a cooler airmass advects in, reinforced with breezy NW winds. Can't rule out a rain/snow shower for the higher elevations if there are any lingering showers on the backside of the system. Not expecting any impacts/accumulation.

The combination of steady east winds and higher astronomical tides raise the risk for splashover for the eastern coastal areas. Surge values range between 0.6-0.8 ft with astronomical tides forecast to be 11.6 ft.

KEY MESSAGE 3...Cooler than normal temperatures for Monday. Although generally dry weather is more likely, monitoring a weak area of low pressure which could bring clouds and scattered showers. Subfreezing low temperatures likely Monday night away from the cities.

Upper level low with an anomalously cold pocket of air aloft still looks to govern Southern New England on Monday. While earlier guidance was indicating dry and blustery weather, there are some recent model forecasts (GFS-based, with a few Canadian ensemble members) which now show a surface trough or weak area of low pressure coming out of the lower Great Lakes early Monday and bringing clouds and scattered showers Monday or Monday afternoon. There isn't a large consensus of members which show this possible outcome, so it remains to be seen if this feature actually has legs or not. Current forecast shows some low chances for showers, and while the showers themselves might not be impactful (some which could be mixed with graupel pellets given cold profiles aloft), it will need to be watched with subsequent guidance as it would shift messaging from what was a mostly clear, blustery and cool day, to a cool and raw day with periods of showers. Highs only in the low to mid 40s in most areas, and if cloud cover does materialize, those values might be a few degrees cooler. Clearing by Monday night, with a near ideal radiational cooling setup looking likely as high pressure settles overhead. Widespread sub-freezing lows looks likely (20s to low 30s), except for the cities which run around the low to mid 30s.

KEY MESSAGE 4...Brief return to seasonable temps on Wednesday, before cooling off again into the latter part of the workweek.

Although it looks like we'll get a brief rebound in temperatures on Wednesday closer to seasonable by Wednesday, our weather pattern still looks unsettled as a cold front moves through later Wednesday or Wednesday night, bringing rain showers. We then get a reinforcing shot of cooler air as northwesterly flow resumes, which should lead to temperatures trending near to below normal again for the latter part of the workweek.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

00z TAF update:

Tonight: High confidence through midnight, then trending moderate on timing.

Other than across Cape Cod/Islands where IFR persists and should remain so, brief window of VFR elsewhere should continue until about 04z. Increasing NE winds draws marine stratus and fog layer westward, soonest at BOS around 06z and continuing to expand westward to BDL through 11z. This will bring IFR-LIFR ceilings and visbys in the 1-3 SM range (possibly 1/2SM at times at BOS and the Cape). Light and variable winds thru midnight, then NE winds around 5-10 kt overnight.

Saturday: Moderate confidence.

IFR-LIFR ceilings early, with improving visbys in fog. Some IFR-MVFR optimism around 15-18z, but ceilings to then trend downward again as we move into the overnight. NE winds 6-12 kt, strongest eastern MA.

Saturday Night: Moderate confidence.

Ceilings deteriorate down to IFR/LIFR levels again Saturday night. NE winds veer around to SE/S 5-10 kt.

Sunday: Moderate confidence.

Mainly IFR-MVFR with steady rain and mist. Outside chance at a rumble of thunder as strong cold front moves through 18-00z. SW winds around 10 kt, becoming W and increasing to 10-15 kt with gusts 23-25 kt post-frontal.

KBOS Terminal...Moderate confidence in TAF. VFR should prevail until about 04/05z, when ceilings deteriorate down to IFR-LIFR levels with IFR mist (periods LIFR visby fog). Fog disperses early in the morning, but IFR ceilings generally persist with some guarded optimism on improvement to IFR/MVFR levels. Light winds become NE 5-10 kt.

KBDL Terminal...High confidence in TAF. VFR through at least 07z, then ceilings become MVFR-IFR as stratus moves in from well offshore. Better chance at ceilings around MVFR-VFR levels during the afternoon.

Outlook /Saturday Night through Wednesday/...

Sunday: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

Sunday Night: VFR. Breezy. Slight chance RA.

Monday: VFR. Breezy. Slight chance RA, slight chance FZRA.

Monday Night through Tuesday: VFR.

Tuesday Night through Wednesday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

High confidence through the weekend.

Seas 2-4 ft and winds less than 25 kts out of northeast today and Saturday. Localized 5 ft seas possible in the southern waters today; not expected to be persistent enough for Small Craft Advisories. Passage of stronger cold front Sun should bring SCA conditions to at least outer waters Sun into Mon. Wind gusts may locally approach 25 kt late Sunday in the outer waters.

Outlook /Saturday Night through Wednesday/...

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

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain.

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

Tuesday: Winds less than 25 kt.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.