textproduct: Boston / Norton

WHAT HAS CHANGED

Small lowering of shower/thunderstorm chances for Thursday.

KEY MESSAGES

- Rip current risk continues along the east coastal areas into this evening. - Small chance of a shower or thunderstorm through this evening across the interior, otherwise tranquil weather through Wednesday night. - Unsettled weather returns Thursday with high pressure and pleasant weather following for Friday - Another round of unsettled weather possible for the second half of the weekend.

DISCUSSION

KEY MESSAGE 1...Rip current risk continues along the east coastal areas into this evening.

Swell energy coming in from the east has been resulting in rip currents along primarily east facing beaches today. This energy will slowly be diminishing this evening and overnight. As that happens, the risk for rip currents along primarily east facing beaches will also slowly diminish.

KEY MESSAGE 2...Small chance of a shower or thunderstorm through this evening across the interior, otherwise tranquil weather through Wednesday night.

Although it's taken awhile, much of the low clouds across the eastern half of southern New England have finally started to lift and break up. Satellite imagery shows daytime cumulus developing across the interior thanks to relatively abundant low level moisture. However the latest mesoanalysis does not show much mixed layer CAPE and still some CIN due to a weak inversion aloft. Although a shower or isolated brief thundershower is possible, the chances are pretty low. Did maintain continuity with previous forecasts and painted in a roughly 20% chance, mainly across the Worcester Hills into NE CT and northern RI. This is where the thermal gradient (due to slightly cooler temperatures where the low clouds hung around longest and where more sunshine has developed) will also be maximized. Otherwise, the next 36 hours will be dry for the vast majority of the region. Could be another round of low clouds and some fog across southeast MA/Cape/Islands late tonight due to the still somewhat humid airmass. Otherwise models are all consistent with dry weather tomorrow. With plenty of sun and 925mb temperatures around 20C, we should see surface temperatures either side of 30C (ie: mid 80s F). Stuck with model blend for that reason. Quiet and seasonable conditions continue Wednesday night.

KEY MESSAGE 3...Unsettled weather returns Thursday with high pressure and pleasant weather following for Friday

Guidance continues to show a shortwave moving east towards the CWA on zonal flow Thursday. Aloft, the jet stream becomes cyclonically curved placing our region under the jet's left exit region. These mid and upper level dynamics provide ample forcing for precipitation. The caveat here will be dry low and mid level moisture profiles across much of the region. Thus, expecting mainly light showers across the southern portion of the CWA with mostly cloudy skies elsewhere. Still, there are some discrepancies within guidance suites. Namely, the global models, including the NBM, show a drier solution with probs of QPF exceeding 0.25" less than 30%. In contrast, CAMs show a more amplified, moisture-rich wave with locally heavy rain and a low risk for thunderstorms. Think the solution lies somewhere in between the two extremes with scattered showers possible mainly along and S of the Mass Pike Thursday afternoon and evening.

The frontal wave passes E of the region late Thursday. Dew point temperatures crash into the upper 50s Friday as high pressure builds overhead. Temperatures will likely be in the low 80s and down to the mid 70s, particularly along the coasts where onshore winds will keep it slightly cooler.

KEY MESSAGE 4...Another round of unsettled weather possible for the second half of the weekend.

Guidance shows an even larger shortwave arriving from the Great Lakes later Saturday with plenty of upper-level energy. Behind the lead shortwave, a series of shortwaves moving along the boundary that may stall just off the east coast could bring chances for showers. Thunderstorms could be a possibility depending on if these waves could take advantage of daytime heat. More details will become apparent as we approach this timeframe. At the moment, guidance blends show a 30-50% chance of rain through much of the interior and 60-70% along the coast from Saturday night to Monday morning.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

18z TAF Update...moderate confidence

Trending toward VFR in most areas. Could see an isolated SHRA or even -TSRA across parts of the interior through 23z. Felt chances were only barely high enough to include PROB30 at ORH and PVD. Most difficult aspect of the forecast is the risk for another round of low clouds and fog overnight. Guidance has backed away from previous depictions of widespread IFR/LIFR, so the TAFs were also trended that way. Any low clouds/fog that does form should be gone 12-14z tomorrow. Otherwise light surface winds that will slowly transition to southwesterly late tonight and Wednesday morning. Otherwise VFR expected tomorrow and tomorrow night. Could be an east coast sea breeze tomorrow afternoon.

KBOS Terminal...Moderate confidence in TAF. Expect MVFR conditions to develop late tonight. Perhaps ceilings becoming IFR.

KBDL Terminal...Moderate confidence in TAF. There is a very small (10%) chance for -SHRA this afternoon, but not enough to include in TAF.

Outlook /Thursday through Sunday/...

Thursday: VFR. Slight chance SHRA.

Thursday Night through Friday Night: VFR.

Saturday: VFR. Chance SHRA.

Saturday Night: Mainly VFR, with local IFR possible. Chance SHRA.

Sunday: Mainly VFR, with local IFR possible. Chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Through Thursday...High confidence.

Generally light winds into Thursday with only weak pressure patterns. Seas will continue to diminish as the swell energy slowly diminishes.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt.

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

Saturday through Saturday Night: Winds less than 25 kt. Rain showers likely, slight chance of thunderstorms.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents until 8 PM EDT this evening for MAZ007- 015-016-019-022-024. RI...None. MARINE...None.