textproduct: Boston / Norton

WHAT HAS CHANGED

Rip Statement issued for east facing beaches of MA for Saturday due to increased risk for rip currents.

KEY MESSAGES

- Any lingering showers exit the Cape and Islands by late morning, giving way to a dry afternoon and evening. Fall-like temperatures expected Saturday with dry conditions.

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

DISCUSSION

KEY MESSAGE 1...Any lingering showers exit the Cape and Islands by late morning, giving way to a dry afternoon and evening. Fall-like temperatures expected Saturday with dry conditions.

The remaining batch of showers continues to push east early this morning. Any remaining showers will likely exit the Cape and Islands by late morning. Behind the showers, a cold front moves across the region early this morning shifting winds to the NW. High pressure will settle across the region for today with subsident flow supporting dry conditions and clearing skies. NW winds with some gusts to 20 and up to 25 mph for the Cape/Islands. Cooler air begins to advect in from the north in the mid-levels later today, but likely won't have much impact on the high temperatures. Temperatures are likely to be in seasonable ranges in the 70s for most areas. Only exceptions may be upper 60s for the outer Cape and Nantucket where there is northerly onshore flow.

A cooler airmass pushes into the region later Friday into Saturday. Clear skies will optimize radiational cooling as well to make for a cool night. Temperatures likely fall into the upper 40s to low 50s for much of the region. Higher elevations, especially the northern Worcester Hills will lean cooler in the low 40s. Cooler airmass stays in place for Saturday with 850mb temperatures 6-9C. This will support Fall-like temperatures in the mid 60s for most. East/northeast flow along the eastern coastline may keep those immediate coastal areas cooler in the low 60s. Surface high pressure continues to dominate bringing dry conditions.

Not exactly ideal beach weather with the cooler temperatures; however, there is an increased risk for rip currents for the east- facing beaches. There will be an extended period of enhanced NNE winds tonight into Saturday which will help establish a swell with slightly longer wave periods.

KEY MESSAGE 2...Next chance for rain Sunday into Monday. There remains uncertainty in the details such as coverage, timing, and amounts. Showers may linger through early next week.

The main surface high exits offshore Saturday night into early Sunday as the next system approaches from the west with our next chance of precipitation Sunday into Monday. The ingredients are generally in place for at at least a soaking rainfall across southern New England. A shortwave approaches from the northwest coupled with an 850mb jet positioning over southern New England. This provide ample moisture advecting and synoptic scale lift for precipitation. PWATS increase to 1.0-1.8" (150-180 percent of normal), which is anomalous compared to climo. A low pressure system tracks east from the Great Lakes region Sunday putting southern New England in the warm sector as its warm front shifts northward. With the ample moisture and additional forcing this raises some flags for heavy rain potential or at least embedded heavy showers.

There is still variance across guidance in the exact track of the system/low pressure which has resulted in lower confidence in the details such as timing, amounts, and the potential for heavy rain. There has also been lacking consistency run to run within individual guidance as well. There is at least a general consensus across guidance that the higher moisture and better forcing(warm front) will more likely be south. This would favor our more south, southwest areas for higher rain totals. GFS and Canadian solutions (deterministic & ensemble) seem to reflect that pattern with higher amounts south while the ECMWF has a wider footprint with generally higher totals. When it comes to amounts solutions vary from 0.30" to 1.0" across ensembles based on the 25-50th percentiles. Deterministic guidance had displayed more "aggressive" solutions with swaths of higher amounts >1.0". However, these solutions have had the most variance from run to run which further adds to the uncertainty. The most likely case at this point will be anywhere from a few tenths to an inch. This seems reasonable given the mean track. There isn't much indication of instability which should limit the heavier rain rates. If the warm frontal forcing shifts north enough, we could get embedded heavy rain supporting by the added lift and efficient rain processes. So overall, there is confidence that we will get at least a soaking rain with rain arriving through the day Sunday continuing into Monday. We'll need to continue monitoring for the isolated heavy rain potential as models come into better agreement with the track over the next day or so.

It is also possible showers may linger across the south coast and Cape and Islands Monday into Tuesday. This will depend on if the low or a boundary stalls across the waters. Wednesday leans mainly dry with potential for another system to arrive late-week with rain possible.

AVIATION /08Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

06Z TAF Update:

Through 12Z...Moderate confidence.

MVFR with patchy areas of IFR and spotty VFR ceilings. Showers push across Cape and Islands, exiting by 13Z. SW winds 6-12 kts with a few occasional gusts to 18 kts in spots. Winds shift to NW 06-12z with gradually improving ceilings. Moderate confidence is with respect to the ceilings. It is possible ceilings scatter more quickly behind the frontal passage. Current TAF keeps lingering MVFR through 13-14Z before scattering out.

Friday and Friday Night...High confidence.

Areas of MVFR linger across Cape Cod and the Islands through 15z, otherwise VFR. NNW winds 8-12 kt with an occasional gust up to 20 kts. There may be an additional period of gusts around 20 kts in the evening (after 00Z).

KBOS Terminal...Moderate confidence in TAF.

Cold front moves through between 07-10Z shifting winds to the NW. Ceilings this morning bounce between low end VFR and MVFR with improvements to solid VFR once the front pushes through. Lower confidence on exact timing, but should be likely be VFR by 13Z. Winds increase after 15Z to 8-12 kts with a few gusts around 18 kts today. Very low probability for a sea breeze to sneak in before 15Z before the winds increase. The current pattern should make this unlikely.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday through Saturday Night: VFR.

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, patchy BR.

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA likely, isolated TSRA, patchy BR.

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

Monday Night: VFR. Windy with local gusts up to 30 kt. Chance SHRA.

Tuesday: VFR. Windy with areas of gusts up to 30 kt. 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.

Showers exit the coastal waters by the afternoon. Seas remain 2-3 ft increasing to 3-4 ft early Saturday morning up to 5 ft across the outermost waters. Winds shift to the NW this morning with speeds 8-15 kts and gusts to 20 kts this afternoon. Briefly Friday night into early Saturday, gusts may approach Small Craft Advisory criteria briefly. Gusts 20-25 kts are possible generally between 03Z and 09Z. Due to it being very borderline and in brief duration, no SCA has been issued.

Outlook /Saturday through Tuesday/...

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

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

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

Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely, isolated thunderstorms, patchy fog.

Monday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

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

Tuesday: Strong winds with gusts up to 40 kt. Seas up to 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents from Saturday morning through Saturday evening for MAZ007-015-016-019-022. RI...None. MARINE...None.