textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Cool, quiet, and dry weather prevails through the first half of Sunday. Expect Highs in the 60s with a chilly start to Saturday morning, especially in the typical cold spots.

- The next quick moving round of rain comes Sunday afternoon and evening, continuing overnight and exiting by Monday morning.

- Quick round of rain around mid week, then dry weather returns by Thursday.

DISCUSSION

KEY MESSAGE 1...Cool, quiet, and dry weather prevails through the first half of Sunday. Expect Highs in the 60s with a chilly start to Saturday morning, especially in the typical cold spots.

A broad mid level trough slowly traverses overhead Friday as high pressure ridging approaches from the west. This places SNE beneath a NW 30-35 kt LLJ; with good mixing (bufkit showing to near 850mb) expecting a gusty day today, much like Thursday. Otherwise, beautiful, mostly sunny weather expected with highs in the mid 60s and a mix of diurnal clouds. High pressure continues to expand and move east, directly overhead by Saturday afternoon giving a very nice start to the holiday weekend with sun, light winds, and highs in the 60s. Something to watch will be how quickly that pressure gradient weakens because light/calm winds overnight would allow for efficient radiational cooling. Thus, leaned on MOS guidance for Saturday morning low temperatures.

KEY MESSAGE 2...The next quick moving round of rain comes Sunday afternoon and evening, continuing overnight and exiting by Monday morning.

The main change from 24 hours ago is both a slightly quicker arrival and exit of the rain. Guidance is in agreement that the moisture left over from what used to be Hurricane Isaias will be pulled east by a northern stream trough and quickly ushered through the mid Atlantic and offshore. There is less agreement as to exactly how far north the precip shield is, but continuing to expect southern New England to be well within the area that will see rain. One one hand, parts of the area (especially west) likely have to deal with rain showers Sunday afternoon/evening. 8PM Sunday ensemble guidance indicates a 80-90% chance of at least 0.01" rain for western MA/CT, but only 40-50% for far eastern MA. On the other hand, by Monday morning there's a good agreement the rain has exited east so it should be a mostly overnight event. On the whole this looks to be a fairly typical rainfall producing system for the region without hazards from flooding or damaging winds. Guidance generally paints a picture of a half inch for northern MA to 1+" along the south shore in closer proximity to the better forcing and moisture. While EPS ensemble probabilities of >1" of rain have increased to max 40-50% along the immediate south coast, GEFS probs put the odds at essentially NIL; needless to say, uncertainty remains on who will see the most rain and how much.

KEY MESSAGE 3...Quick round of rain around mid week, then dry weather returns by Thursday.

A break in the rain comes Monday into Tuesday under brief high pressure ridging before another frontal system moves through bringing a round of wet weather. Confidence in any timing or placement details is low and will depend on how this holiday weekend's system plays out but unsettled weather looks possible around late Tuesday or Wednesday.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

06z TAF Update...High confidence.

VFR conditions continue through Saturday. W wind 10-15 kts gusting to 20 to 30 kts Friday through the afternoon. Diurnal cloud deck around 045 possible. Winds light and variable on Saturday.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: VFR.

Sunday: VFR. Chance SHRA.

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA.

Columbus Day: Mainly VFR, with local IFR possible. Slight chance SHRA.

Monday Night: VFR.

Tuesday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Saturday: High confidence.

W winds will increase through the morning, peaking in the afternoon. Expecting sustained winds 10-15 kts with gusts 20-25kts though some gusts 25-30 kt are possible. Seas around 4 ft or less Friday for all waters, with good visibility expected. High pressure overhead Saturday leads to seas 2 ft or less with N winds 5-10 kts.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt.

Sunday: Winds less than 25 kt. Chance of rain showers.

Sunday Night: Winds less than 25 kt. Local rough seas. Rain showers, slight chance of thunderstorms.

Columbus Day: Winds less than 25 kt. Rough seas up to 9 ft. Chance of rain showers.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

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