FXUS61 KBOX 040548 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1248 AM EST Wed Dec 4 2024 .SYNOPSIS... Dry and cold weather continues tonight and Wednesday...but a few brief snow showers may impact parts of interior southern New England into early this evening. An Alberta Clipper will bring accumulating snow to the high terrain northwest of I-495 Wednesday night into Thursday morning with mainly rain on the I-95 corridor. A strong cold front may bring a few snow squalls Thursday and also result in strong winds developing. Blustery and colder Thursday night and Friday with temperatures well below normal. It remains cold Saturday but with less wind, then a moderating trend begins Sunday with above normal temperatures returning early next week. Mainly dry weather expected through the weekend, then rain chances will increase early next week as a frontal system approaches from the west. && .NEAR TERM /THROUGH TODAY/... * A few brief snow showers will dissipate this evening * Otherwise...dry and cold tonight with lows teens to the lower 20s * Sunshine gives way to clouds Wed with highs upper 30s/near 40 Scattered snow showers are moving eastward across CT and will move into RI and possibly adjacent areas in SE MA before dissipating this evening. The snow showers will be accompanied by brief vsby restrictions and may bring a coating of snow. These snow showers are assocd with a mid level shortwave and leftover lake moisture. As the shortwave moves to the east later tonight, expect clearing skies. This combined with winds becoming calm/light from the NW should allow for a good night of radiational cooling. Overnight low temps should bottom out in the teens to the lower 20s in most locations with middle 20s in the Urban Heat Island of Boston. Wednesday... An Alberta Clipper will be dropping southeast across Ontario on Wed. Sunshine during the first part of the day...will give way to increasing clouds during the latter half of the day. Temps will again be chilly/below normal for this time of year. Highs will mainly be in the upper 30s/near 40 with readings a bit cooler in the higher terrain. && .SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/... Key Points... * Accumulating Snow higher terrain northwest of 495 Wed night/Thu AM * Ptype mainly rain towards & especially southeast of I-95 * Greatest uncertainty with Ptype is across interior lower elevations * A strong cold front may bring a few snow squalls later Thu * Turning quite windy Thu afternoon & night with NW gusts 35-50 mph Details... Wednesday night into Thursday morning... The Alberta Clipper will be moving across Quebec and northern New England Wed night into Thu morning. This will induce a strong southwest LLJ at 850 mb of 45 to 60 knots. There is also a good signal for a period of modest mid level frontogenesis ahead of this clipper system. This should allow widespread precipitation to overspread the region from west to east between 8 pm and midnight. In addition...this strong southwest LLJ should mix quite well near the south coast given relatively chilly boundary layer temps. Thinking southwest winds will gust to between 30 and 40 knots later Wed night towards the Cape and Islands. May even be marginal Wind Advisory criteria for parts of this region. Ptype/Snow Accumulations... The main question is Ptype across the region Wed night into Thu morning. Given that this storm is passing to our north and there is no cold high pressure system in place to our north...southwest flow will allow for boundary layer to warm nicely along the Boston to Providence corridor. Ptype in this region should mainly be rain. Some of the guidance indicates rain could end as a bit of snow...but do not think it will amount to much if anything. Thermal profiles & soundings indicate that the boundary layer will remain cold enough to support mainly snow in the high terrain to the northwest of I- 495. We are thinking 2-5" of snow across much of the interior high terrain across western and central MA with perhaps isolated 6" amounts in the highest terrain. We have gone ahead and issued a Winter Weather Advisory for these locations. The main concern will revolve around the Thu morning commute where roads may be snow covered and slippery. Confidence on Ptype is more uncertain in the lower elevations particularly in the Springfield to Hartford areas. We could struggle to get much accumulation if boundary layer trends warmer...but if rates are able to overcome that warmer boundary layer may get a quick few inches. So in a nutshell...we are confident in accumulating snowfall across the interior high terrain and mainly rain along the I-95 corridor...although a bit of snow is possible before the precipitation ends Thu morning. The greatest uncertainty in Ptype/Snow amounts is across the lower elevations of the interior...especially in the Springfield to Hartford metro areas. Later Thursday morning and afternoon... While the steady rain and snow will have exit most of the region by mid-late Thu morning...a strong cold front will follow. This will be associated with a strong shortwave/steep low level lapse rates in the 1000-700 mb layer along with a fair amount of low level moisture left over. In fact...the guidance is showing a few hundred J/KG of MUCape. Therefore...a few snow squalls will be possible on Thu with brief localized very poor visibility and strong wind gusts. The primary concern for travel issues will again be across the interior where temps will be colder and snow may quickly coat roads in any localized snow squalls. We will have to monitor this closely over the next 24 hours. Towards the I-95 corridor boundary layer may be warm enough for a mix of scattered rain/snow showers. Otherwise...a strong westerly low level jet coupled with cold advection will result in the development of strong winds. Wind gusts on the order of 35 to 50 mph are expected to develop later Thu into Thu evening. Wind Advisories may be needed for portions of the region. High temps in the upper 30s to the middle 40s will fall later in the day and evening as strong cold advection takes over. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Key messages: * Blustery and colder Thursday night and Friday * Still cold Saturday but with less wind * Moderating temps Sunday warming to above normal early next week * Mainly dry through the weekend, then rain chances return early next week Details... Thursday night through Sunday... Arctic front will be offshore by Thu evening with gusty W winds bringing in a rather chilly airmass Thu night and Fri as 850 mb temps bottom out around -13 to -15C Fri. Temps well below normal Fri with highs upper 20s and lower 30s for much of SNE. The cold will be accompanied by gusty W winds 25-40 mph which will drive wind chills down into the teens and low 20s on Fri. Not quite as cold Sat but still below normal (highs in 30s) with less wind, then temps begin to moderate Sunday as SW flow develops. A few snow showers may linger into Thu evening over the Berkshires, otherwise mainly dry conditions expected through the weekend as high pres gradually builds east to the mid Atlc coast. Monday and Tuesday... Forecast confidence decreases early next week as a pattern change develops with a shift to SW flow aloft as upper trough digs into the Rockies. A series of fast moving shortwaves lifting NE toward New Eng will bring a risk of showers at times early next week but timing is uncertain. We have higher confidence in a warming trend with above normal temps likely returning as notable warming occurs in the low levels. Temps will likely get back into the 50s for at least a portion of SNE, especially on Tue. This is supported by GEFS/EPS/CMC ensembles which all indicate high probs of temps above 50F by Tue, especially south of the MA Pike. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAF Update... Today...High Confidence. VFR. Winds becoming SSW at 5 to 15 knots. Tonight through Thursday Night...Moderate Confidence. Precipitation overspreads the region from west to east this evening between 00z (west) and 06z (east). The exception will be over eastern MA and RI terminals where there is a chance for some earlier scattered light RA/SN showers as early as 22Z. The precipitation will result in widespread low end MVFR- IFR conditions developing with LIFR conditions possible across the interior as the night wears along. As the widespread precipitation departs Thu morning...conditions should improve to mainly MVFR and even VFR in some spots Thu afternoon. Ptype will mainly be snow northwest of I-495 with generally rain southeast of that region Wed night into Thu morning. Ptype could mix with or change to snow towards the I-95 corridor for a brief time before the bulk of the precipitation ends Thu morning. Snow accumulations of 3-6" are expected across the interior high terrain with 1-3" in the lower elevations of the interior. Little if any snow accumulations on the I-95 corridor with precipitation mainly in the form of rain. The steady precipitation will come to an end Thu morning...but a strong cold front will bring a few rain/snow showers and the potential for a couple of heavier snow squalls too. SSW winds at 5-15 knots are expected tonight...but will be stronger on the order of 15 to 30 knots with perhaps some gusts up to 40 knots later in the night towards the Cape and Islands with a strong LLJ. Winds shift to the west on Thu with gusts of 30-40 knots developing behind the strong cold front. KBOS Terminal...High confidence in TAF. Some wet snow flakes may occur briefly or mix in with rain showers 23-02z but confidence is low. KBDL Terminal...High confidence in TAF. Outlook /Thursday Night through Sunday/... Thursday Night: VFR. Strong winds with areas of gusts up to 45 kt. Friday: VFR. Windy with gusts up to 35 kt. Friday Night through Saturday Night: VFR. Breezy. Sunday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. * Gale Warnings Wed night and Thu Tonight and Wednesday...High Confidence. Northwest winds on the order of 10 to 15 knots tonight will shift to the southwest on Wednesday. This a result of an Alberta Clipper dropping southeast across Ontario. Winds/Seas will generally remain below small craft advisory thresholds...but may see some southwest wind gusts of 20-25 knots across the southern waters by late Wednesday and perhaps some marginal 4-5 foot seas. Wednesday night and Thursday...High Confidence. A strong southwest LLJ ahead of an Alberta Clipper will allow southwest wind gusts of 30 to 40 knots to develop Wed night and then shift to the W behind a strong cold front Thu. In fact...we may see some gusts up to 45 knots on Thu behind a strong cold front. Gale Warnings have been posted for all our waters. Outlook /Thursday Night through Sunday/... Thursday Night: gale force winds with gusts up to 45 kt. Rough seas up to 14 ft. Slight chance of rain showers. Friday: Strong winds with gusts up to 35 kt. Rough seas up to 11 ft. Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Saturday: Winds less than 25 kt. Seas up to 5 ft. Saturday Night through Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Winter Weather Advisory from 8 PM this evening to 10 AM EST Thursday for MAZ002>004-008>010-012-026. RI...None. MARINE...Gale Warning from 7 AM Thursday to 7 AM EST Friday for ANZ230. Gale Warning from 7 PM this evening to 7 AM EST Friday for ANZ231>237-250-251-254>256. && $$ SYNOPSIS...KJC/Frank NEAR TERM...KJC/Frank SHORT TERM...Frank LONG TERM...KJC AVIATION...KJC/BW MARINE...KJC/Frank