085 FXUS61 KBOX 030709 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 309 AM EDT Sun Oct 3 2021 .SYNOPSIS... Cold front along the NH border will move south through Srn New England today, reaching the South Coast by evening and offshore tonight. Low pressure wave moves up the front tonight and Monday, bringing rain/showers to the region. Local downpours are possible Monday into Tuesday. Drier and seasonable weather returns midweek before possibly more unsettled weather heading into next weekend. Dangerous rip currents at the coast due to distant Hurricane Sam will continue through at least Sunday night. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Cold front along the Northern border of MA divides southwest winds to the south and east winds to the north. A 110-kt upper jet moves across Northern New England, placing Southern New England in the right entrance region of the jet later today. This will support lift, and when combined with increasing PW values...reaching 1.5 inches by evening...this should bring an increasing chance of showers especially in Western MA and CT. East winds behind the cold front will bring a moist flow off the Gulf of Maine, generating low cloudiness in eastern MA that will spread westward with time. The east wind will keep mixing shallow and temperatures in the upper 60s and low 70s. The southwest wind south of the front will support warmer afternoon temperatures, in the mid 70s. Surfers and late season beachgoers should remain aware of the increases threat of dangerous rip currents on ocean beaches and coastlines today and tonight. This comes from long period swell from distant Hurricane Sam. Greatest risk will be on south-facing beaches, but the threat will extend up the Massachusetts East Coast. Know what to do to escape a rip current, namely, swim parallel to shore. Beaches are no longer guarded this late in the year. More info can be found at weather.gov/safety/ripcurrent. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Overview... Cold front moves south of the region. Two upper disturbances move past the region, Generating a wave of low pressure along the front for Monday. This will bring two surges of rain...one overnight and the second on Monday. Details... Tonight... As noted above, one upper jet moves across Nrn New England today and early tonight, placing Srn New England under the right entrance region and supporting lift. PW values of 1.5 inches settle over the region tonight. Expect developing rain/showers, highest values in Western MA/CT. Some potential for minor urban/poor drainage flooding in the CT Valley late at night. Rain and the east low-level flow will generate areas of fog overnight. Expect temperatures near the dew point, in the 50s and low 60s. Monday... Second upper jet and shortwave move up the Eastern Seaboard, generating lift and a second round of rain/showers. A wave of low pressure forms along the cold front to our south, focussing overrunning over the front and across Srn New England Monday and Monday night. PW values remain around 1.5 inches, supporting local heavy rainfall. Concerned with the combined rainfall of the two periods of rainfall, which will be 1 to 2 inches and possibly higher in spots. The amount may threaten local flooding, but extending it over Monday and Tuesday may reduce the effect of the rainfall. With east flow, expect max temps only a few degrees higher than the overnight low. Will forecast upper 50s and 60s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Period of moderate to heavy rain possible Monday into Tuesday night, with potential for minor flooding. Several commutes may be impacted. * Mainly dry and seasonable early fall weather returns Wednesday into Thursday. * More unsettled weather possible heading into next weekend. The main concern for this portion of the forecast remains the possibility for moderate to heavy rainfall Monday into Tuesday. Lots of features will play a role in this rainfall potential. Chief of which will be a blocking high pressure over southeast Canada and the North Atlantic. Where this high pressure sets up will shift the axis of heaviest rainfall to its south. Its orientation will also be a factor in how long rainfall may linger across our region. At present, only have moderate confidence in the details for the Monday and Tuesday forecast. That said, the latest guidance continued to show precipitable water values between 1-1.5 inches. Most of the guidance also hinted at two waves of precipitation: one Sunday night into Monday, and the other Monday night into Tuesday. Still some opportunities for tweaks to this timing. Rainfall-wise, thinking total amounts through Tuesday of three quarters to one and one half inches is likely. Then there is the 12Z NAM scenario, which cranks out up to 4 inches of rainfall by Tuesday evening. The NAM to this point is an outlier solution, even surpassing the 95th percentile of the NBM at times with its accumulations. So, have not yet jumped on that bandwagon. Will have to keep it in mind as a possibility, though. Once we get into mid week, high pressure should be firmly in control before moving offshore Friday. Some risk for another coastal low pressure to impact or region with more rainfall Friday night into Saturday. Still a lot of time to get though before nailing down those details. Expecting slightly below normal temperatures into Wednesday, rising to near normal after then into next weekend. && .AVIATION /07Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today... VFR most of the day, but lowering to MVFR ceilings toward evening. Light winds becoming east-northeast around 7 knots. Tonight...MVFR lowering to IFR ceilings and vsbys in rain and fog. Monday... IFR ceilings and vsbys in rain and fog. Isolated TSRA along the South Coast. KBOS Terminal...High confidence in TAF. VFR. Ceilings lower to MVFR around 23Z and to IFR around 03Z. KBDL Terminal...High confidence in TAF. VFR. Ceilings and vsbys lower to MVFR around 02Z and to IFR around 06Z. Outlook /Monday Night through Thursday/... Monday Night: IFR. SHRA likely, patchy FG, isolated TSRA. Tuesday: Mainly IFR, with areas VFR possible. Chance SHRA. Tuesday Night: MVFR/IFR conditions possible. Slight chance SHRA. Wednesday: Mainly VFR, with local IFR possible. Wednesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Thursday: VFR. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. A cold front moves south from Northern MA today, reaching the South Coast by evening. Winds will shift from the east-northeast after the front moves through. Winds on the southern waters will remain southwest today, then shift from the east tonight. Increasing wind tonight in the east flow, with speeds 15 to 20 kt. This continues on Monday. A few showers possible this evening. Most of the rain starts tonight and continues Monday. Vsbys around 3 miles in rain and fog. Concern continues for rip currents along the coast from distant Hurricane Sam. A 14-second period swell of four feet lingers along the South Coast. A High Rip Current Risk Statement...CFWBOX...continues in effect. Small Craft Advisory continues in effect for southern and southeast waters. The headline for the outer waters continues through early Sunday night. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Seas up to 5 ft. Rain showers likely, patchy fog. Visibility 1 to 3 nm. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Wednesday Night through Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Rip Current Risk through late tonight for MAZ007-015-016- 019>024. RI...High Rip Current Risk through late tonight for RIZ005>008. MARINE...Small Craft Advisory until 6 AM EDT early this morning for ANZ235-237. Small Craft Advisory from 10 PM this evening to 6 AM EDT Monday for ANZ250. Small Craft Advisory until 6 AM EDT Monday for ANZ254-255. Small Craft Advisory until 10 PM EDT this evening for ANZ256. && $$ SYNOPSIS...WTB/Belk NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Belk AVIATION...WTB/Belk MARINE...WTB/Belk