160 FXUS61 KBOX 120001 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 701 PM EST Sat Dec 11 2021 .SYNOPSIS... A warm front approaches New England from the south, crossing Southern New England during the morning. This will bring a period of light rain and some fog. A cold front then approaches from the west late today and tonight, bringing showers and a few thunderstorms as well as local downpours. Blustery and dry Sunday into Monday with above normal temperatures. A warm front may bring limited chances for precipitation Wednesday. Even milder temperatures and continued largely dry weather expected for late in the week, ahead of a cold frontal passage later Friday or early in the weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 645 PM Update: Made a few adjustments to PoP and Wx to better refine the timing of the cold front following current observed upstream trends and the latest HRRR/NAM-3km guidance. While southerly gusts have fallen just short of Advisory levels (around 35-45 mph across SE New England), west gusts should reach Advisory levels across a larger part of Southern New England at more regularity. The take away message is a period of more active weather is likely between 9 PM and 1 AM, with gusty post frontal winds and possible instances of sporadic wind damage. See recent SPS issued for awareness which includes approximate timing. Regarding the winds - driven mostly by impressive isallobaric pressure rises on the order of 7-10 mb per 3 hrs and lower-level stability profiles becoming unstable due cold advection, gusts across western NY in the post-frontal air mass have been between 35-55 mph. While the upper trough remains positively tilted meaning less ascent, we still anticipate a shallow fine line of at least brief heavy showers to mark the cold front. While it is a lower probability, I did add a mention of isolated thunder as I did note the 12z HREF has a ribbon of 200-400 J/kg of CAPE in the warm sector across southern/southeast MA and RI. This looks to a pool of observed dewpoints upper 50s/near 60F. If it appears more obvious that convective processes in the fine line could transport especially stronger winds to the surface, short- fused statements could be needed to address this. So, a brief period of heavy showers with a gusty wind shift between 9 PM - 1 AM. We then expect a period of gusty west winds behind the front for the midnight to early-overnight period, with sharp pressure rises and cool advection lifting the existing temperature inversion and permitting gusts closer to the wind advisory levels. Recent HRRR reflect gusts that may reach as high as 55 mph in spots especially Worcester and Tolland Hills into the Berkshires; sometimes the HRRR's gust progs can overdo things but it can speak to an upper-bound gust outcome. It is appearing more likely the after-midnight period is when gusts capable of damage may ensue. By pre-dawn, gusts should begin to subside to around 25-35 mph coinciding with the end time of the Advisory. A fairly mild night now across all of SNE as cold air has finally eroded with temps pre-frontal in the 50s to lower 60s. Temps then fall behind the front to lows by daybreak in the 30s to lower 40s. Previous discussion: The warm front has kicked up to central MA early this afternoon, with 60 degrees at Norwood and 36 F at Fitchburg at 2 PM. As the parent low lifts further northeast into Quebec the front will continues to lift north, and with that we see a lull in the rainfall and unsettled weather for much of the afternoon and early evening. The next chance of rain and convection comes ahead of the cold front, which has slowed down a bit. Hi-res guidance now shows the cold front entering western MA/CT until 3Z (10 PM). Thus we'll see a line of rain and potential for some thunder just ahead of the forcing, after 1Z (8 PM), exiting eastern MA by 4 AM. Given several hundred J/kg of CAPE we could see some lightning with this line as well which would have the potential to exacerbate gusty wind concerns in a localized area. Speaking of winds, a Wind Advisory remains in effect for southern New England for the potential for winds gusting to 45 mph through the overnight and early morning hours. Winds will really kick up with the passage of the cold front eroding the 850 mb warm nose/inversion. Post frontal winds out of the northwest will continue to be gusty well into Sunday. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday kicks off a prolonged stretch of benign weather with the return of riding mid level heights and a building surface high pressure over the entire east coast. Temperatures will be notably colder than our anomalous warmth from Saturday, in the mid to upper 40s (much closer to normal for mid december). While the core of the low level jet will have moved off, good mixing to near 900 mb under cool NW flow will allow for a breezy day, gusting 25 to 30 mph. Sunday night is quiet with clear skies, but winds won't decouple which will keep radiational cooling from being maximized; looking at lows near or just below freezing. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights: * Mild and dry weather prevails at least until Wed nite/early Thurs. Highs commonly in the upper 40s to lower 50s with lows around or above freezing each day. * Warm front Wed nite/early Thurs may bring round of light rain. * Even milder air returns Thurs, highs some 10 to 15 degrees above normal! * Unsettled Sat with better chances for precip; uncertainty on precip type but odds favor wetter vs wintry conditions. Overview: Strong confidence continues in a rather lengthy spell of mild and generally dry weather that will govern expected conditions through much of the upcoming workweek. In fact by late in the week (particularly Thursday), a period of well above normal temperatures looks to be in the offing under strong SW flow. Weather pattern turns more unsettled late in the week into the weekend. Details: A 1030 mb high pressure centered over southern Virginia to begin on Monday allowing for dry conditions with westerly breezes. Highs should reach well into the 40s high terrain to the low to mid 50s. Passing cool front well to the north Monday night will bring a wind shift to NW, with modest cool advection. However flood of mild Pacific air maintains above-normal temps on Tuesday in the 40s to low 50s. Will have good radiational cooling Tues night, likely to be the coolest night in the workweek with lows within a few degrees of freezing. Increasing clouds Wednesday into Wednesday night/early Thursday associated with a warm front. Decent burst of isentropic lift but appears the bulk of this is mainly focused across interior New England or at worst as far south as areas north of the Mass Pike. In addition, though some pockets of shallow cooler air are possible in the typical trouble spots such as the Merrimack Valley, northern Worcester County into Pioneer Valley, given the milder spell of weather it is not viewed as likely we'll see sub-freezing temps supporting any wintry mix. Cloudy but dry weather prevails Wed nite to Thurs AM. The rest of Thursday features decreasing clouds, breezy SW winds and warming temperatures. 925 mb temps Thurs off the 12z ECMWF are in low teens Celsius range. Blended in some of the 90th percentile NBM guidance in to boost highs over NBM values under at least partial sun into the low to mid 60s! Friday into the weekend turn more unsettled and confidence in details starts to dwindle. In the wake of a cold frontal passage Friday, southeast CONUS mid-level ridge appears to be maintained with an overrunning low moving NE from the Ohio Valley early in the weekend, bringing another round of decent chances for PoP. Question is how much cooling occurs post-frontal on Friday to dictate initial p-type. Considering this is a Day-7 forecast, still enough time to sort through those details but given a track to our west, tilt in the odds toward more liquid than frozen precip. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 00z TAF Update: Tonight: Moderate confidence. MVFR-IFR cigs with southerly winds 15-20 kt, gusts mid to upper 20s for the interior, 35-40 kt in southerly gusts Cape and Islands until frontal passage. Cold front will bring about a brief period of MVFR +SHRA, but a gusty wind shift to W with gusts commonly around 30-40 kt for most airports. Timing between 02-07z with rapid improvement to VFR accompanying the gustier conditions. Gusts ease to 25-30 kt by daybreak. Sunday... Colder, drier air moves in from the west. Wind gusts diminish to 25-35 kt. VFR skies. Sunday night... VFR. Light to breezy SW winds. KBOS Terminal...Moderate confidence in TAF through 00Z. High confidence beyond 00Z. KBDL Terminal...Moderate confidence in TAF through 00Z. High confidence beyond 00Z. Outlook /Monday through Thursday/... Sunday Night through Monday Night: VFR. Breezy. Tuesday through Tuesday Night: VFR. Wednesday: Mainly VFR, with local MVFR possible. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. This afternoon...Moderate confidence. Winds from the south-southwest 20-30 kt sustained and 40-45 kt gusts. Light rain this morning, diminishing this afternoon. Showers approach from the west toward evening. Gale Warnings remain in effect this afternoon and evening. Tonight...Moderate confidence. A cold front moves across the waters between 03Z and 08Z. Expect showers and scattered thunderstorms ahead of the front with strong wind gusts and with local downpours and fog reducing visibility. South-southwest winds gust 40 to 45 kt ahead of the front, turning from the west later at night. Seas 10-15 kt, especially on the outer waters. Gale Warnings continue in effect tonight. Sunday...High confidence. Drier air with clearing skies expected. Wind gusts diminish, but still reach 30-kt. Seas diminish, reaching 5-7 feet in the afternoon. Small Craft Advisory will likely be needed. Sunday Night...High confidence. Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Outlook /Monday through Thursday/... Monday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Monday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Tuesday through Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday: Winds less than 25 kt. Seas up to 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory until 5 AM EST Sunday for CTZ002>004. MA...Wind Advisory until 5 AM EST Sunday for MAZ002>024-026. RI...Wind Advisory until 5 AM EST Sunday for RIZ001>008. MARINE...Gale Warning until noon EST Sunday for ANZ231>235-237-250-251- 254>256. Gale Warning until 7 AM EST Sunday for ANZ230-236. && $$ SYNOPSIS...Loconto/BW NEAR TERM...Loconto/BW SHORT TERM...BW LONG TERM...Loconto AVIATION...WTB/Loconto/BW MARINE...Loconto/BW