textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Dry weather with cooler than normal temperatures tonight through Tuesday night.

- Unsettled weather returns later Wednesday. Widespread showers Wednesday night and Thursday with lingering showers possible Friday.

- Warmer temperatures return this weekend. Potential for isolated to scattered showers and perhaps a thunderstorm.

DISCUSSION

KEY MESSAGE 1...Dry weather with cooler than normal temperatures tonight through Tuesday night.

Cold front from early this morning along the southeast waters is still bringing a canopy of midlevel cloudiness to most of Southern New England. This front will be slowly trudging southeastward through early tonight; sfc ridge of high pressure then builds in from the northwest through Tuesday, under midlevel troughing associated with a cool airmass works its way in.

Clearing skies for tonight and a gradually slackening northwesterly wind should allow for at least some radiational cooling. 925 mb temps around +2 to +4C are rather cool for this time of year and temps under clear/calm conditions could allow for temps supporting a light frost in NW MA; there are mixed signals though on if winds will really drop below 5 mph and if we'll stay fully clear. NAM and GFS show a 500 mb vort maximum now over Michigan moving ESE through Southern New England late tonight into the overnight, which could bring at least some enhanced cloudiness and/or keep winds mixed enough to preclude frost from developing. The frost/freeze program is now active in all zones in Southern New England, but I think the above caveats are enough where frost headlines probably won't be necessary for northwest MA. A few areas in northwest MA could drop into the mid to upper 30s, but lows elsewhere in the upper 30s to mid 40s.

High pressure then continues to build in on Tuesday, with mostly clear skies, dry weather and northwesterly breezes. Seabreezes are likely on both southern and eastern coasts by late morning, but it's otherwise a cool but pleasant Tuesday with highs mid 50s to lower 60s. Bit warmer temperature profiles for and increasing cloud cover should support somewhat milder nighttime lows Tuesday night in the mid 40s.

KEY MESSAGE 2...Unsettled weather returns later Wednesday. Widespread showers Wednesday night and Thursday with lingering showers possible Friday.

High pressure shifts offshore during the day Wednesday ahead of an approaching shortwave trough. Deterministic and ensemble guidance has shown sufficient agreement with a 500mb low cutting off from the deep trough as it moves across eastern Great Lakes then tracking eastward toward southern New England late-week.

Flow becomes southwesterly Wednesday ahead of the trough with a plume of slightly above normal moisture advecting in through the day. Moisture generally appears to arrive late morning-afternoon with showers developing sometime in the afternoon. Timing remains uncertain still; however, across most model guidance there is a consensus with shower chances increasing from west to east through Wednesday afternoon. A round of rain is possible in the afternoon followed by more widespread showers/rain developing Thursday night. Rain likely continues through the day Thursday. The mid-level closed low and surface low stay fairly stacked and shift just offshore or across southeast southern New England late Thursday into Friday. Most model guidance is leaning slower improvements on Friday as the low slowly exits, especially in eastern areas. This may keep scattered showers around at least the first half of the day.

In terms of rain amounts, ensembles show a range 0.40" to around 1.0" as more likely. The ECMWF ensemble leans on the wetter side compared to the GEFS with the ECMWF ens 75th percentile showing potential for areas to receive 1.0 to even 1.25" while the GEFS tops out under 1.0" within their respective 75th percentile. Regardless, this is looking like an overall beneficial rain for most areas of southern New England. Temperatures mid to late week will lean cooler than normal.

KEY MESSAGE 3...Warmer temperatures return this weekend. Potential for isolated to scattered showers and perhaps a thunderstorm.

The upper trough and low exits the region by Saturday morning with a mid-level ridge moving in from the west during the day. Across ensemble guidance, this ridge brings along the signal for temperatures moderating Saturday with above normal temperatures for Sunday. There is potential for a few shortwave troughs to move through the flow over the weekend. Timing and strength of the waves are uncertain at this time which will factor into the precipitation chances. For now, see it as a low probability (< 30%) for a round or two of isolated to scattered showers and perhaps a thunderstorm. There is not signal for widespread activity or heavy rainfall at this time.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Through 00z Tuesday: High confidence, though closer to moderate on seabreeze potential.

VFR. NW winds around 8-12 kt with occasional gusts to 20 kt thru at least 21z, but possible period of lighter winds could allow for E MA seabreeze to develop at BOS by 21z. If it doesn't then NW winds should continue for BOS around 10 kt.

Tonight: High confidence.

VFR; there could be some lower-VFR decks and perhaps a sprinkle or light shower at absolute worst 03-09z BDL-PVD south and east. NW winds around 5-10 kt, though becoming 5 kt or less overnight.

Tuesday and Tuesday Night: High confidence.

VFR. NW winds around 7-10 kt, with seabreezes for BOS and PVD developing around 15-16z. Winds become light WNW/W overnight.

KBOS Terminal...High confidence in TAF. Potential 120/130 degree wind directions around 10 kt after 21z thru 02z. Otherwise, NW winds prevail.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Saturday/...

Wednesday: VFR. Breezy. Chance SHRA.

Wednesday Night: Mainly VFR, with local IFR possible. Breezy. SHRA, patchy BR.

Thursday: Mainly VFR, with local IFR possible. Breezy. SHRA, slight chance TSRA.

Thursday Night: Mainly VFR, with local IFR possible. Chance SHRA, slight chance TSRA, patchy BR.

Friday: VFR. Chance SHRA, slight chance TSRA.

Friday Night: VFR. Chance SHRA.

Saturday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

High confidence.

Winds and seas to remain below small craft advisory criterion through Tuesday night. NW winds increase some to around 15 kt tonight, then continue around 10-15 kt Tue and Tue night. Seas 4 ft or less all waters.

Outlook /Tuesday Night through Saturday/...

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain showers, slight chance of thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, patchy fog.

Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

Friday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

Saturday: Winds less than 25 kt. Seas up to 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

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