Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220023 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 723 PM EST Wed Feb 21 2018 .SYNOPSIS... A cold front moves through Southern New England early tonight. Much colder weather then moves in for Thursday. The front stalls south of New England Thursday, an area of unsettled weather moves along the front and across Southern New England. This will bring a mix of precipitation, with snow and sleet north of the Mass Pike while rain and sleet falls to the south. An active wet weather pattern Friday through the weekend during which there is the possibility of mixed precipitation, freezing rain late Friday into Friday night and again around Saturday night into Sunday. Dry weather will follow. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Dense fog is beginning to scour out across the south coast per observations and area webcams. Thus will let the dense fog advisory expire. Otherwise, cold front is quickly swinging into the region as it currently from LWM to BDL. Once the front moves through, southwest winds will quickly switch to the northwest and gusts between 25-35 MPH. Anticipate these gusts to continue for an hour or two until the pressure gradient relaxes. Temperatures behind the front are also dropping with locations across the Berkshires already into the 50s and the CT valley not to far behind them. Thus temperatures will fall through the night as CAA continues to take hold of the region. Lastly, while moisture is a bit meager along this front, still cannot rule out a few isolated showers across the interior. However, closer to the south coast, good line of showers with some thunder moving across NH and into the lower Hudson Valley of NY. Expect these showers to continue to develop along or ahead of the front into southern CT and potentially southern RI and the Islands. Thus have put in sct showers into the forecast. This front will stall just south of the region which could result in periods of showers for the immediate south coast, Cape and Islands through the night. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... 730 PM Update... Latest trends in the guidance suggested a cooler scenario for Thursday event. Thus went ahead and updated the forecast to reflect these trends. Quick moving wave will ride along the stalled front south of the region, and with CAA continue to push through, expect more of an isothermal transfer of temperatures within the profile. Thus mid and low level temperatures will cool leading to more of a snow/sleet profile than rain as shown in BUFKIT model soundings. Still have to watch for a warm layer around 800mb, but feel that precip will fall hard enough that the profile should maintain frozen precip (snow/sleet). All said in done, north of the Pike may see some sleet but will transition to all snow by the afternoon. Could see around 1-3 inches on elevated surface. Snow will struggle to stick on area roadways as they are quite warm thanks to the 70+ degree day today. Along and south of the Pike expect more of a mixed bag of precip leading to rain to sleet to snow to a low chc of freezing rain. Lastly along the south coast, could see rain at first, but if precip falls hard enough then could transition to sleet with the potential for some freezing rain. Overall confidence is higher with snow and sleet outcome than with any freezing rain. But if there is a chc for FZRA than winter weather advisories may be needed as it only takes a T. Previous Discussion... The cold front stalls over the Mid Atlantic coast and south of New England Thursday. High pressure from the Plains then moves to the Great lakes Thursday, maintaining the colder temps over our area and setting up a cool northeast flow off the Gulf of Maine. The right entrance region of the upper jet will be in position just as this colder air pushes south. All of this will provide sufficient lift to generate an area of precipitation that moves up from the Ohio Valley. The challange with this forecast is determining precip type. No cold air damming signal in the data. there is just the infiltration of cold air with the high pressure and the northeast wind off the marine environment. We are maintaining snow and sleet north of the Mass Pike and rain south of the Pike and along the eastern coast. Accumulations will be light, with the best chance of minor accumulations across the higher elevations of Northern Mass. Confidence in precipitation is moderate-high, but confidence in precip type is low-moderate. As noted on the previous forecast, a warmer solution would mean more rain and less snow/sleet. Thursday night... The precipitation moves offshore, and high pressure builds over Northern New England. The high center moves to the Maritimes by 12Z Friday with a cold air ridge extending southwest through New England. Low level moisture lingers over Southern New England, which should keep clouds south of the Mass Pike overnight. Northern Mass could have partial clearing for a few hours. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Highlights... * Burst of precip with wintry mix in the interior Fri night * Dry but warm as Spring returns on Saturday * Widespread precip on Sunday with wintry mix in the interior * Dry weather trend for early next week Overview... 12z guidance is in general agreement with the extended forecast. Just some minor differences related to thermals which provide different outcomes in p-type. Deep trough across the western CONUS with ridging over the Eastern Seaboard. This puts the region in southwest flow allowing for Gulf moisture to stream into the area. Ridge will begin to flatten out as subtropical high begins to retreat back west towards the Gulf of Mexico by the end of the period. A few waves of low pressure will move through the flow with the first one Friday night followed by one on Sunday. Thereafter pattern begins to breakdown as ridge moves over the Great Lakes region and cut-off low begins to set-up over the Maritimes. This could result in a return to average to below avg temps mid to late next week. Details... Friday into Saturday...Moderate confidence. Retreating high pressure as baroclinic zone remains south of the region. Dry weather to start but with front near by an approaching WAA anticipate showers to develop and expand by the late afternoon hours. Thermals will be tricking as WAA moves through bringing in a good warm nose per BUFKIT soundings. Biggest question is the surface temps and if they will warm above freezing as high pressure is retreating resulting in more of a easterly flow rather than the classic northerly cold air damming. The GFS appears the warmest of the guidance in terms of 2M temps keeping p-types as mainly rain. This does appear to be an outlier compared to the NAM/EC and CMC. While hi-res data would give this forecast more confidence, appears that the trend is increasing in a period of freezing rain during the evening commute, esp in NW interior MA. Precip will come to an end by the overnight hours as another front pushes into the region an stalls just south of the area. With this front near by, a few showers are possible early Saturday morning, but strong high and ridging overhead will help result in a dry forecast. Despite westerly to northwest flow, surface temps could potentially warm into the low to mid 50s by the afternoon. However, depending on where frontal system stalls, temps could actually rise or fall. Thus a low confidence forecast for temps on Saturday. Saturday night into Sunday...Increasing confidence. Last wave will eject out of the desert southwest producing surface low pressure system up into the northern Great Lakes. Another shot of overrunning precip as warm front approaches from the south. Again depending on thermals, we could see a chc for freezing rain at the onset. This system looks to bring the most QPF out of all the system so expect widespread precip, esp as we continue to tap into that Gulf moisture. One thing to watch is the development of a surface low along the front. This could help drag in more cold air from the north leading to a changeover from rain to sleet/snow on Sunday. Still some uncertainty with this forecast because of the thermals in question. But cannot rule out wintry precip during this period. The front will quickly push through resulting in a drying trend for late Sunday night. Monday and beyond...Moderate confidence. High pressure will build across the region Monday and last into early next week. Temperatures will be seasonable to slightly above average as the pattern begins to shift. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/...Moderate confidence. Tonight... IFR fog lingers over Cape Cod and Islands in the evening, but should lift by 03z. Cold front is pushing through the region switching SW winds to a NW direction. Behind the front winds will quickly pick up around 20-30 kts, but should only last an hour or two. VFR conditions remainder of Southern New England. Thursday... VFR in the morning. Winds turn from the northeast. Clouds lower and thicken as an area of precipitation moves in from the west. Afternoon cigs/vsbys lower to MVFR in snow/sleet north and light rain south. -SN accumulation possible north of the Mass Pike. Potential for -PL/RA south of the Pike. Low confidence in -FZRA. Thursday night... Rain/sleet/snow moves offshore along with the low clouds. Most of the night should be VFR with continued northeast winds. KBOS Terminal...High confidence TAF. VFR through Thursday morning. Cigs/vsbys lower to MVFR in the afternoon with PL and SN. KBDL Terminal...High confidence in TAF. Cigs/vsbys lower to MVFR in the afternoon in rain, possible mixing with sleet. Outlook /Friday through Monday/...Moderate confidence. Friday: Mainly MVFR, with local IFR possible. RA, slight chance FZRA across interior NW MA. Friday Night: MVFR/IFR conditions possible. Chance RA, chance FZRA across interior NW MA.. Saturday: VFR. Saturday Night: Mainly MVFR, with areas VFR possible. Breezy. RA. Sunday: Mainly MVFR, with local IFR possible. Windy with local gusts to 30 kt. RA. Sunday Night: Mainly VFR, with local MVFR possible. Breezy. Chance RA. Monday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/...Moderate confidence. Tonight... Fog is slowly shifting east. This will bring improving vsbys over the waters this evening and early tonight. Cold front moves across the waters early tonight, then stalls south of the waters. Southwest winds shift from the northwest and then north overnight. Winds gusting near 25 kt this evening, then 20 knots or less after the front moves through. Seas at 5 feet will subside overnight. Small Craft Advisory for wind and rough seas on most waters this evening and on the outer waters through midnight. Thursday... Winds turn from north and then northeast with gusts to 20 knots at times. Seas mostly below 5 feet, except near 5 feet on the outer edge of the outer waters. Rain moves in from the west during midday and afternoon. Could be some mixing with sleet especially along the North Shore of Mass. Thursday night... High pressure centered over Canada moves to Maine and the Maritimes overnight. Rain moves off to the east. Northeast winds continue with gusts 20 knots or less. Seas less than 5 feet. Outlook /Friday through Monday/... Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Saturday: Winds less than 25 kt. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Rain likely. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Rain. Sunday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain. Monday: Winds less than 25 kt. Local rough seas. && .CLIMATE... Daily record high temps have been set at all four climate site. Records for all-February have been set at Hartford and Worcester. High temperatures through 3 pm... Boston.....72..Daily record 63 (1906)..Feb record 73 (2/24/2017) Hartford...74..Daily record 63 (1930)..Feb record 73 (2/24/1985) Providence 64..Daily record 63 (1930)..Feb record 72 (2/24/1985) Worcester..71..Daily record 59 (1930)..Feb record 69 (2/24/2017) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 9 PM EST this evening for ANZ235- 237. Small Craft Advisory until 1 AM EST Thursday for ANZ250- 254>256. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...WTB/Dunten SHORT TERM...WTB/Dunten LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten CLIMATE...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.