textproduct: Boston / Norton

WHAT HAS CHANGED

A Rip Current Statement has been issued for Plymouth and Barnstable Counties for Saturday.

KEY MESSAGES

- Misty with drizzle today ahead of heavier rain tonight into Sunday.

- Drier and warmer next week.

DISCUSSION

KEY MESSAGE 1...Misty with drizzle today ahead of heavier rain tonight into Sunday.

Low pressure has continued to bring scattered light showers and drizzle/mist across parts of the Cape and south coast tonight as it has continued trekking northeast, while more interior parts of the region have remained mostly dry. This trend should continue to start the day. Based on latest observations, the low is centered just south of Nantucket as of the time of writing this discussion. Guidance remains in agreement with the general track of this low after it remained further south of Long Island than initially forecast; it will curve up and around the Cape and Islands through the day today, moving up into the NH/ME coast into Sunday morning. Misty conditions with periods of drizzle remain the main story for today as a result of prevailing cyclonic flow. Some CAMs hinted at a brief period of showers in the late morning to afternoon hours, with some even showing them passing through the interior. Highs today will likely not get out of the low 70s for southern New England.

Heavier rainfall moves through tonight, generally after midnight, as the low continues on. PWATs remain elevated, approaching 2.0" towards SE MA and the Cape and Islands. IVT remains favorable for heavier showers, though the more anomalous values should remain further offshore. With regards to rainfall totals, ensembles top out at around a 20% chance of totals meeting or exceeding 1" in 24 hours ending Sunday over the Cape and Islands. The exception remains the GEFS, which continues to be drier than the other ensembles. Ensembles have somewhat trended higher totals slightly more offshore over the last few runs while deterministic guidance has somewhat varied more from run to run. The HREF PMM has 24 hour totals getting to around 0.75"-1" over the same area, including into parts of RI and SE MA; 48 hour totals could reach 1.5". High-res guidance indicates streaks of higher totals stretching northeast across the coastal plain, but this could change depending on just how close to land the low tracks while it cuts around Cape Cod.

Overcast and misty conditions with periods of drizzle remain the story for Sunday as well as the low continues north and a front starts to approach from the west. Ahead of this front, the flow turns more southerly to southwesterly. This will advect in more moisture from the south and increase dewpoints into the 70s. PWATs approaching 2.0" and higher will filer in as well. Notably, CAMs have MUCAPE values approaching 1500-1700 J/kg with limited CIN over the interior for Sunday afternoon. 0-6 km shear approaches 50 kt with effective bulk shear around 35 kt. All of these parameters combined with any possible forcing from the front could set the stage for some scattered thunderstorms, some of which could turn strong to severe over the interior. With more southerly flow as well, highs Sunday increase back into the upper 70s and low 80s.

KEY MESSAGE 2...Drier and warmer next week.

Sunday's cold front shifts offshore for Monday. Post-frontal passage, much drier air and warmer temperatures take hold with more westerly winds, clearing out clouds and dropping dewpoints through Wednesday. The base of the trough tracks directly overhead into Tuesday and heights rise behind it as it continues eastward, though a weak shortwave may track through and bring a low chance of diurnal showers. High pressure continues building into the region into the middle of next week and flow aloft becomes more zonal. Low pressure developing over the Great Lakes towards the second half of the week may play more of a role later in the week, but for the time being, no major disturbances are expected through Thursday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

12z TAF Update:

Today...Moderate confidence.

Primarily MVFR or low end VFR ceilings. Patchy IFR ceilings remain a possible towards SE MA/Cape and Islands. Periods of mist and drizzle for immediate east coast and Cape/Island terminals. Few -SHRA possible over the Cape/Islands. Winds generally NE to N at 5-12 kt.

Tonight...Moderate confidence.

Widespread IFR should overspread the region heading into tonight with areas of LIFR possible, especially for Cape/Islands. -SHRA and -DZ possible overnight. Exact timing is lower confidence. Winds NE/E at 5-10 kts.

Sunday...Moderate confidence.

MVFR-IFR ceilings with periods of showers during the day. Scattered TSRA possible in the afternoon hours. Winds shift more S to SW after 21Z ahead of an approaching cold front.

KBOS Terminal...Moderate confidence in TAF. Conditions should deteriorate to MVFR, then remain there through the day. Periods of mist and drizzle possible throughout the day as well. Few -SHRA possible overnight with a rounds of showers Sunday morning. Low chance for an embedded thunderstorm in the late afternoon/evening.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR. Slight chance SHRA.

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Sunday...High confidence.

NE to N winds generally 15-20 kts and seas 3-4 ft through most of today become more light variable today into tonight as the low breaks down into Sunday morning. Winds then shift more S for Sunday at around 5-10 kt, gusting to just under 20 kt occasionally during the afternoon.

Despite the lower wave heights, the prolonged northeasterly flow will cause higher swells and longer swell periods today which is why a Rip Current Statement for Plymouth and Barnstable Counties will be in effect. Eastern, ocean-facing beaches will be primarily affected, especially across the northern portion of Cape Cod; however, bay-facing beaches may also experience rip currents. Swells diminish for Sunday, and the risk for rip currents decreases with them.

Outlook /Sunday Night through Wednesday/...

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

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

Monday Night through Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Wednesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents until 6 PM EDT this evening for MAZ019- 022. RI...None. MARINE...None.