textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Dry with fall-like temperatures today and tonight.

- Rain likely Sunday into Monday, although there still remains uncertainty in the exact amounts. Showers may linger through early next week. A coastal system is possible late week.

DISCUSSION

KEY MESSAGE 1...Dry with fall-like temperatures today and tonight.

A cooler airmass settles over the region early this morning resulting a cool start to the day today with temperatures in the 40s and 50s this morning. Expect dry conditions today with surface high pressure in place. The cooler airmass stays put with 850mb temperatures 6-9C. This will support fall-like temperatures in the mid 60s for most, flirting with 70 in the CT Valley. Northeast flow with likely keep the immediate eastern coastal areas cooler in the low 60s. Tonight, high pressure begins to shift offshore as our next system approaches from the west. With cloud cover not increasing until sunrise, there should be enough of a window with clear skies and light winds to support efficient cooling tonight. Temperatures likely fall into the 40s for a good part of southern New England. CT and RI may end up a little warmer as WAA begins to push in after 2AM which would limit their window of cooling.

The extended period of NE winds will help develop a swell with longer wave periods across the eastern waters for today. This will increase the risk for rip currents for the east-facing beaches including Nantucket today. If you plan on heading to the beach despite the cooler temperatures, please use caution.

KEY MESSAGE 2...Rain likely Sunday into Monday, although there still remains uncertainty in the exact amounts. Showers may linger through early next week. A coastal system is possible late week.

Model guidance continues to stay in general agreement to support rainfall Sunday into Monday. A shortwave approaches from the northwest coupled with an 850mb jet positioning over southern New England allow advection of moisture from the south and increased lift. PWATS increase to 1.2-1.8", around 160-180 percent of normal. 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 its cold front trailing from the west, this should provide sufficient convergence for widespread rainfall. Model guidance has consistently been indicating lacking instability with this system which would likely limit the rain rates and thus limit the threat for heavy rain and flash flooding. There is still some spread in expected totals liking owing to track differences, but ensembles show a more likely range of a few tenths to around 1 inch. Some solutions such as the ECMWF/ensemble indicate potential for greater than 1.0" with ensemble probabilities of 20-50% along the east slope of the Berkshires. Other solutions lean lighter with amounts 0.25-0.50". 3 and 6 hour QPF doesn't approach FFG, but some pockets of moderate or very brief heavy rain are possible. In terms of timing, rain likely spreads from west to east Sunday morning with widespread rain arriving by the afternoon. Rain continues overnight into Monday.

How long the rain lingers Monday will depend on how progressive the system/front is. There are difference across guidance in the speed which has led to some uncertainty in how long showers linger around on Monday. If showers were to linger, it would more likely effect areas more south and east (Cape/Islands or south coast). Fall-like temperatures are likely behind the front on Monday with breezy northerly winds. There is potential for another system to brush southern New England Tuesday bringing showers; however, this is lower probability as there lacking agreement with how north this system tracks at this time.

There is good agreement across model guidance with a fairly strong surface high shifting over Quebec Tuesday into mid-week. This will keep a cooler than normal airmass over the northeast supporting cool more fall-like temperatures continuing through the week. Deterministic and ensemble guidance continues to hint at the potential for a coastal low pressure system sometime Thursday into Friday. However, there is still a fair amount of uncertainty in the details of the pattern that will influence the track of this low. Some solutions feature a low track closer to southern New England while others well off shore. Pretty low confidence at point, but warrants monitoring as it would bring potential for stronger winds, rough seas for the coastal waters and potentially another round of rainfall.

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...High confidence.

VFR. Light NE winds becoming E/ESE in the afternoon, except for occasional 20 kt gusts in the morning across the Cape and Islands. These are expected to drop off through the day today.

Tonight...High confidence.

VFR. Winds shift to the S in the evening less than 10 kts. Some areas may go calm.

Sunday...Moderate confidence.

VFR to start, diminishing to MVFR and IFR in the afternoon as rain moves into the region. LLWS could be a concern after 18z as this system pushes through. Winds generally SE at 5-10 kt towards the surface. Chances for TS are low to near zero.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

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

Monday: Mainly VFR, with local MVFR possible. Breezy.

Monday Night through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Windy with local gusts up to 35 kt.

Wednesday: VFR. Strong winds with local gusts up to 40 kt.

MARINE

Forecaster Confidence Levels...

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

Tonight through Sunday...High confidence.

As high pressure builds into Quebec tonight, expect a period of N wind gusts 20-25 kts through mid to late morning. Otherwise winds decrease through the day out of the NE/E. Seas 2-4 feet, approaching 5 ft for the far outer coastal waters.

Next chance for SCA conditions Sunday night and Monday, potentially continuing into Tuesday. We are currently monitoring potential for a coastal low pressure later next week (Thu-Fri). There is uncertainty in the track of the low this far out and thus the potential impacts. A closer track would raise the threat for strong winds and rough seas. Stay tuned.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rain showers.

Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

Monday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of rain showers.

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of rain showers.

Tuesday Night: Strong winds with gusts up to 40 kt. Rough seas up to 11 ft. Slight chance of rain showers.

Wednesday: Strong winds with local gusts up to 45 kt. Rough seas up to 13 ft. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents through this evening for MAZ007-015-016- 019-022-024. RI...None. MARINE...Small Craft Advisory until noon EDT today for ANZ231-232-250- 251-254>256.