textproduct: Boston / Norton

WHAT HAS CHANGED

Increased uncertainty regarding shower potential Wednesday.

KEY MESSAGES

- Seasonable temperatures and comfortable humidity Wednesday. Low chance for a few showers for the south coast and Cape and Islands Wednesday. Otherwise, dry.

- Rain chances increase later Thursday into Friday as a front lingers near the south coast of New England. High pressure then returns drier and cooler weather for this weekend. Rain chances may increase again early next week as a low pressure passes through.

DISCUSSION

KEY MESSAGE 1...Seasonable temperatures and comfortable humidity Wednesday. Low chance for a few showers for the south coast and Cape and Islands Wednesday. Otherwise, dry.

Most areas are likely to remain dry for the remainder of the afternoon and evening. The one exception is the chance for a stray shower or storm to make it into northwest CT late afternoon/early evening. Overnight temperatures fall into the 60s with periods of cloud cover.

There is still lower confidence in the potential for an offshore low pressure system to brush across the southern portion of southern New England on Wednesday. This has been reflected amongst deterministic and ensemble guidance with some solutions developing a low pressure that tracks north to bring showers to the south coast and Cape/Islands. Other solutions don't develop a "stronger" surface low at all or track it too far south to bring shower chances to southern New England. GEFS probabilities for > .01" range 30 to 60 percent with probabilities dropping off quickly as you move north of the immediate coast. ECMWF probabilities are > 20%. The NAM and RRFS have trended the most north bringing a more robust batch of shores across at least south and southeast southern New England. Given the spread here, worst case will be a some light showers Wednesday AM/early afternoon with the greater risk for the south coast and Cape/Islands. If this system passes mainly south, expect a drier day. With flow aloft becoming more zonal, temperatures cool slightly bringing more seasonable highs Wednesday in the low to mid 80s.

There will likely be a shift to a more unsettled weather pattern late Wednesday into Thursday with indications of a frontal boundary stalling across a portion of southern New England. A few embedded weak disturbances ride this boundary, resulting in periods of showers arriving as early as overnight Wednesday night.

KEY MESSAGE 2...Rain chances increase later Thursday into Friday as a front lingers near the south coast of New England. High pressure then returns drier and cooler weather for this weekend. Rain chances may increase again early next week as a low pressure passes through.

Still some timing differences to be worked out Thursday into Friday. Most of the latest global guidance suite has a cold front near the south coast of New England Thursday morning. The differences arise from how quickly this front gets south enough of our region to no longer be a factor in our weather. The consensus approach keeps this front close to the south coast into Friday morning, but this timing could be quicker, leading to a drier day Friday. Not a lot of humidity to work with, but thinking there is at least a risk for diurnal showers and thunderstorms. A good portion of this time should remain dry for most.

This front should finally push offshore later Friday, allowing high pressure to build across southern New England. This leads to drier and cooler conditions this weekend. The timing for early next week is not certain as well. While there are some differences in the timing, the overall consensus is for a low pressure to move across northern New England some time Monday. This system should be off to the east by Tuesday. This timing could change with later forecasts.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

Through 00Z...High confidence.

VFR. WNW to NW winds 8-12 kts with an occasional gust to 18 kts this afternoon. Low chance (< 15%) for an isolated shower or storm to be in vicinity of BDL after 21Z through 00Z.

Tonight...High confidence.

VFR. Winds generally out of NW less than 10 kts. There is a low probability for a shower for the Islands (< 20%).

Wednesday...High confidence.

VFR. Light N/NW winds. Easterly sea breeze develops for BOS and other east coast terminals 14-17Z. There is a low chance (10-20%) for a few showers along the immediate south coast and Cape/Islands 09-15Z with "greater risk" for the Islands (ACK). Otherwise, dry conditions for other terminals.

KBOS Terminal...High confidence. Wildfire smoke aloft possible.

KBDL Terminal...High confidence. Wildfire smoke aloft possible.

Outlook /Thursday through Sunday/...

Thursday: VFR. Breezy. Slight chance SHRA.

Thursday Night: VFR. Slight chance SHRA.

Friday through Friday Night: VFR. Breezy.

Saturday through Saturday Night: VFR.

Sunday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Winds and seas below SCA criteria through Wednesday. NW winds tonight become easterly Wednesday 10-15 kts. Seas 3 ft or less.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt.

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

Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Friday Night through Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Saturday Night through Sunday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

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