textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Dry and seasonably cool conditions through the first half of Wednesday.

- Unsettled midweek pattern with increasing chances for beneficial rainfall.

- Warm and mainly dry weekend pattern, but details remain uncertain.

DISCUSSION

KEY MESSAGE 1...Dry and seasonably cool conditions through the first half of Wednesday.

An amplified mid-level trough shifts offshore today, yielding fair-weather cu and abundant sunshine. Despite sunshine, cool conditions persist with 850mb temps near -1C to +1C, supporting highs in the upper 50s to mid 60s. A weak pressure gradient brings uncertainty to sea breeze development across eastern Massachusetts. Otherwise, NW winds remain around 8 to 12 mph with generally quiet conditions expected. CU diminishes this evening, followed by increasing clouds overnight ahead of the next system. Cloud cover will limit radiational cooling, with lows Wednesday morning mainly in the 40s. Dry weather persists for many through at least the first half of Wednesday as high pressure shifts offshore and low pressure develops over the eastern Great Lakes.

KEY MESSAGE 2...Unsettled midweek pattern with increasing chances for beneficial rainfall.

High pressure shifts east Wednesday as the next system approaches from the west. Flow turns SW, advecting higher moisture with PWATs increasing to 0.8 to 1.0 inches across southern New England by late morning. Latest guidance supports an earlier onset of precipitation, generally mid to late morning, as a warm frontal zone lifts through the region. Best forcing initially focuses across western MA and northwest/north-central CT. After a possible relative decrease in coverage during the afternoon, rain expands eastward late Wednesday into Thursday (primarily after 00Z) as a longwave trough becomes cut off over northern New England and southern Quebec before slowly drifting southeast toward the region Friday. As the mid-level and surface lows become vertically stacked, widespread unsettled conditions persist through Thursday, with gradual improvement Friday afternoon as high pressure builds in from the southwest and ridging develops to the west. This system continues to favor beneficial rainfall. Ensemble guidance shows moderate probabilities for 0.5"+ QPF, with ECMWF/CMC ensembles in the 70 to 90 percent range and GEFS lower at 30 to 60 percent. Ensemble percentiles generally support 0.3 to 0.6 inches at the 25th percentile and 0.8 to 1.2 inches at the 75th percentile. Temperatures remain below normal through the period, with highs in the lower to mid 60s Wednesday through Friday. If the cutoff exits faster, Friday could trend milder.

KEY MESSAGE 3...Warm and mainly dry weekend pattern, but details remain uncertain.

Upper trough exits and heights rise into the weekend and early next week, supporting above-normal temperatures with highs in the 70s, possibly approaching 80 degrees in warmer locations. Confidence is lower regarding timing and coverage of any precipitation due to potential embedded shortwaves, but overall trends favor mainly dry conditions with only low-probability scattered showers or thunderstorms Saturday into Sunday. By Monday, an anomalous ridge builds over the Northeast, supporting continued dry and warm conditions into early next week.

AVIATION /14Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

15Z TAF UPDATE:

Today and Tonight...High confidence.

VFR. NW winds 8 to 12 kt. Sea breeze remains possible for KBOS around 16Z, though development may be limited if NW winds remain slightly stronger. Winds become light WNW/W tonight.

Wednesday...High confidence.

VFR early. -RA possible across western terminals late morning. Conditions trend MVFR west to east Wednesday evening with -RA. Winds S 10 to 15 kt.

KBOS...Moderate confidence.

VFR. Sea breeze development possible after 15z to 16Z. Slightly stronger NW flow may keep the sea breeze offshore or oscillating near the coast during the afternoon.

KBDL...High confidence.

VFR.

Outlook /Wednesday Night through Saturday/...

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

Thursday: Mainly MVFR, with local IFR possible. Breezy. SHRA, slight chance TSRA, patchy BR.

Thursday Night: Mainly MVFR, with areas IFR possible. SHRA, slight chance TSRA, patchy BR.

Friday: MVFR/IFR conditions possible. Chance SHRA.

Friday Night: Mainly VFR, with local MVFR possible.

Saturday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Today through Wednesday...High confidence.

Winds and seas remain below Small Craft Advisory criteria through Tuesday night. NW winds 10 to 15 kt today and tonight, with possible sea breeze development nearshore this afternoon. Seas 4 ft or less. Winds shift S Wednesday, increasing to 15 to 20 kt with gusts 25+ kt and seas building to 4 to 6 ft over southern waters. Small Craft Advisory conditions likely Wednesday into Thursday.

Outlook /Wednesday Night through Saturday/...

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

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

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers, slight chance of thunderstorms, 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.