textproduct: Boston / Norton

WHAT HAS CHANGED

Tweaked rainfall chances and timing overnight.

KEY MESSAGES

- Dry weather continues through the evening before the risk for scattered showers and a few thunderstorms returns tonight into Friday.

- Some showers expected Saturday. followed by a warming and drying trend into early next week.

- Warm and humid mid week. Risk for some showers with a warm frontal passage sometime Wednesday into Thursday.

DISCUSSION

KEY MESSAGE 1...Dry weather continues through the evening before the risk for scattered showers and a few thunderstorms returns tonight into Friday.

A weak surface low tracks across New England late this evening. Its associated warm front will also move through, allowing for the chance of showers and thunderstorms to progress from west to east. The risk for thunder remains quite low given the lack of instability present overnight. However, some embedded rumbles of thunder over western MA are possible where a more favorable environment resides.

Updated the timing and coverage this evening based on recent radar data. Many of the high resolution mesoscale models were also more bullish on measurable rainfall, mainly after midnight. Trended the forecast to higher rainfall chances overnight.

These showers will likely dissipate Friday morning as the weakening low shifts further away. It'll feel slightly more humid on Friday with dewpoints in the mid to upper 60s. As another surface low tracks into the region on Friday, this will bring another chance for showers and thunderstorms in the evening/night. It looks like the convection will be fairly scattered and the severe threat remains isolated. Even though instability remains limited, the effective bulk shear looks impressive with values ranging from 40- 50kt. Therefore, the primary concern with thunderstorms that do develop will damaging wind gusts. It is worth noting that southern New England is also under a Marginal (1/5) risk for severe weather Friday.

KEY MESSAGE 2...Some showers expected Saturday. followed by a warming and drying trend into early next week.

Guidance continued to have a similar idea about a low pressure tacking along a cold front. However, the track of this low pressure and front were quite different. The NAM was the most aggressive keeping showers farther north across southern New England. Most of the guidance is farther south. Have the greatest confidence in showers towards the south coast of New England. Still thinking the timing could be off, and Saturday could turn out drier than the current forecast.

Dry weather is expected to return heading into the start of next week as high pressure associated with an amplified upper level ridge moves into southern New England. A warming trend also kicks off for the start of the work week, continuing into midweek. However, details on just how warm it may get are still uncertain at this time.

KEY MESSAGE 3...Warm and humid mid week. Risk for some showers with a warm frontal passage sometime Wednesday night into Thursday.

Increasing heat and humidity continues into the second half of next week. Much of this time is expected to remain dry, but there should be a period of showers with the passage of this warm front. The location details for these showers are not yet known.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

Through This Afternoon...Moderate confidence.

Showers are tracking from west to east this morning and will continue through southern New England through around 14z when they are expected to dissipate. The risk for embedded thunder among these showers has gone down considerably, so TSRA was removed from TAFs before 12z today. Mostly VFR outside of showers and storms today, though areas of MVFR and even some IFR are possible this morning in wake of showers. Risk for fog at ACK remains this morning as well.

The risk for isolated thunderstorms, some of which may turn severe, returns in the afternoon primarily after 21z. PROB30s were included at most terminals to account for this risk. Periods of MVFR visibilities and ceilings possible with any afternoon showers and storms. Uncertainty remains in exact location/overall coverage.

Tonight...Moderate confidence.

Showers and storms should clear the region by midnight. Patchy fog leading to areas of MVFR/IFR may develop overnight across much of SE MA, Cape Cod, and the Islands. Low stratus also a possibility, particularly towards the Cape and Islands. Winds shift more W and go light to calm overnight.

Saturday...Moderate confidence.

Mostly lower end VFR with areas of MVFR. Showers mostly scraping along the south coast are favored; lower confidence in those going much further north than that. These may also approach later in the day than expected. Light winds.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

Saturday Night through Monday Night: VFR.

Tuesday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Friday...High confidence.

Light south-southwesterly winds persist through the afternoon, before shifting more southerly overnight. It's possible to see some breezier winds this evening (gusts up to 20 kt) across the waters. Seas should remain 2 to 4 ft. Showers and thunderstorms may start to impact the waters late tonight into Friday.

Outlook /Saturday through Tuesday/...

Saturday through Saturday Night: Winds less than 25 kt. Chance of rain showers.

Sunday through Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

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