textproduct: Boston / Norton

WHAT HAS CHANGED

No significant forecast changes.

KEY MESSAGES

- Shower chances Thursday evening into Friday morning, followed by drier conditions Friday.

- Drier conditions Friday and Saturday.

- Next chance for rain Sunday into Monday. There remains uncertainty in the details such as coverage, timing, amounts. Showers may linger through early next week.

DISCUSSION

KEY MESSAGE 1...Shower chances Thursday evening into Friday morning, followed by drier conditions Friday.

Clouds are increasing and showers are on the doorstep of southern New England, crossing the region through this afternoon and evening before exiting the coastal waters early Friday morning. These showers are associated with a northern- stream shortwave trough; however, there is less-than-ideal forcing over southern New England. Guidance consensus shows the best forcing/lift across northern Massachusetts (mainly north of Rt. 2) and into southern Vermont and New Hampshire. PWATs are quite anomalous for mid-September, nearing 2+ inches, which is near the maximum of climatology based on sounding climatology at Chatham. Today's suite of high-res guidance is in pretty good agreement that showers move into far western areas of southern New England as early as 3-4 PM, approaching the I-95 corridor between 7-9 PM. The threat of thunder is low, though not zero. There is also a low threat of localized heavy downpours due to the anomalous moisture in the atmosphere, but these showers are moving at a good pace. Nevertheless, rainfall amounts will be highly variable given the showery nature. There is potential for as much as a half inch of rain in the vicinity of Rt. 2 in northern Massachusetts and into southern Vermont and southern New Hampshire, with much less the farther south you go.

KEY MESSAGE 2...Drier conditions Friday and Saturday.

A few early morning showers are possible across Cape Cod and the Islands; otherwise, a transient high pressure system moving out of the southern Canadian Prairies brings a dry stretch of weather Friday and Saturday. Seasonably mild temperatures are expected Friday, with highs in the middle 70s and elevated dew points initially in the lower 60s, though those fall into the upper 40s by Friday afternoon. Breezy NW winds in the afternoon with gusts 20-25 mph, mainly across the interior. Then a shift to more fall-like conditions on Saturday. A chilly start for most, with lows in the lower to middle 40s, while urban areas remain in the lower 50s. Not out of the question that upper 30s occur along the east slopes of the Berkshires and across northern Worcester County. Otherwise, a crisp afternoon with sunshine and highs in the middle to upper 60s. Light east winds will lead to slightly lower temperatures for eastern coastal communities, with locations like Boston perhaps not climbing out of the lower 60s. Dew points in the 40s will add to the crisp feel.

KEY MESSAGE 3...Next chance for rain Sunday into Monday. There remains uncertainty in the details such as coverage, timing, amounts. Showers may linger through early next week.

Still have timing concerns for rainfall Sunday into Monday. While a high pressure should be moving off the coast Saturday night, it may still have too much influence to prevent rainfall from overspreading our region during the morning. Still favoring rainfall arriving from west to east Sunday afternoon into Sunday night. Another high pressure over eastern Canada should become more of an influence over the course of Monday. Thus, not certain how many showers will remain Monday morning. Thinking the greatest risk for lingering showers will be towards the south coast.

The potential rain amounts will depend on the exact track of this low pressure, which is still variable across guidance this far out in time. This variance translates quite clearly to the rain totals across both deterministic and ensemble guidance. Moisture should not be that much of a limitation. Overall, still looking like another soaking rainfall for most. Favoring the highest rainfall totals towards the south coast of New England at this time.

The forecast trend is for drier weather Tuesday and Wednesday. It appears that another low pressure could approach from the Mid Atlantic states sometime towards Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

Through Tonight...Moderate confidence.

Predominantly VFR with areas of MVFR this afternoon. SSW winds at 5-10 kt. Exception is BOS, where ENE winds continue through late afternoon. Showers arrive during the afternoon hours from W to E, with chances continuing to increase through the evening. Showers are more likely to develop after 21z for the western terminals and after 00z for the more eastern terminals. Overnight, MVFR with areas of IFR and patchy fog. Showers continue to move across the region from west to east, exiting the Cape/Islands around 12z. SW winds 5-10 kt, shifting to NW 06-12z as the front moves through.

Friday and Friday Night...High confidence.

Areas of MVFR linger across Cape Cod and the Islands through 14/15z, otherwise VFR. NNW winds 8-12 kt with gusts up to 20 kt, though gusts diminish after sunset. The exception will be the Cape and Island terminals, where gusts continue into the overnight hours. Across the interior, northerly winds less than 5 kt.

KBOS Terminal...Moderate confidence in TAF.

ENE winds become S around 23/00z. SHRA chances increase after 23z; have opt'd for VCSH during that time since probabilities are lower. Higher confidence in SHRA after 01z, continuing through 07/08z with MVFR ceilings, though cannot rule out briefly falling to IFR during periods of SHRA. VFR Friday with NNW gusts up to 20 kt.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday through Saturday Night: VFR.

Sunday: MVFR/IFR conditions possible. SHRA likely.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy. SHRA likely.

Monday through Monday Night: VFR. Breezy. Slight chance SHRA.

Tuesday: VFR. Windy with local gusts up to 30 kt. 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.

A round of showers pushes across the waters tonight into early tomorrow morning. Seas remain 2-3 ft, though portions of the southern waters may approach 4 ft heading into tomorrow morning. Winds shift to the NW tomorrow morning, with some gusts up to 20 kt possible. High pressure builds in from the WNW Friday afternoon and remains with us through Saturday. Briefly Friday night into early Saturday, gusts may approach Small Craft Advisory criteria. Confidence in gusts exceeding 25 kt is low; however, gusts of 20 to 25 kt seem likely. Future forecast updates may include an advisory if confidence in higher gusts increases. Otherwise, nice conditions on Saturday with seas 2-3 ft and ENE winds less than 15 kt.

Outlook /Saturday through Tuesday/...

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

Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Sunday Night: Winds less than 25 kt. Areas of rough seas. Rain showers likely.

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Monday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers.

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

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