Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210018 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 718 PM EST Tue Feb 20 2018 .SYNOPSIS... Mild and humid southwest flow continues tonight and Wednesday. A cold front will then sweep through Southern New England Wednesday night followed by colder weather Thursday. A wave of low pressure tracking along the front may bring some rain Thursday, possibly mixed with snow in the interior. An active wet weather pattern Friday through the weekend during which there is the possibility of mixed precipitation, freezing rain. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Major update to the forecast to account for current trends. Weak meso low as noted in the MSAS surface plot has developed north of Cape Ann. This has allowed for a backdoor front/sea breeze/onshore winds to push into Essex county and Boston. In fact Boston dropped 21F went the winds switched to the northeast and fell from 69 to 48F. Quite a difference and thus appears the the record warmest min temp for today will not be achieved as they did fall to 45F. This combination of the onshore flow with the ocean has also brought in low clouds and fog, especially over the North Shore. Went ahead and issue an SPS for this location as vsbys are dropping between 2 to 1/4 of a mile. Meanwhile, across the south coast, onshore flow will continue to stream in stratus and fog resulting in dense fog for the overnight period. While the Cape is filtering near 1 sm right now and could be over the next few hours, the southerly flow will win and drop them back into the soup. The dense fog advisory looks good for now, but may have to extended it into RI, eastern CT and southeast MA as areas of dense fog may spread per latest HRRR, GLAMP and NBM. Latest, stout inversion will be in place during the overnight with low levels remaining quite moist. May see some patchy drizzle develop with highest confidence across the immediate south coast. Areas that do not have onshore flow and/or fog will remain pretty mild during the overnight hours. Expect min temps to remain in the low 50s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Fog and low clouds to start the day, especially along the south coast. Most fog will burn off during the morning. Clouds and fog may linger longer than indicated along the south coast due to the continued moist flow over the cold water. Mixing depth inland will again be limited by the warm advection aloft. But even a shallow mix to 950 mb taps temps equiv to 850 mb values of 4-6C, and 925 mb shows values of 4-7C. Sfc pressure about 1024 mb would add a couple of deg F, all of which supports a max sfc temp range of 66 to 73 inland. Temps closer to the south coast will continue to be buffered by southwest wind off the ocean, keeping temps in the upper 40s and 50s. Given sufficient sunshine and heating, Wednesday will have potential for record high temps. Records are listed in the Climate section. Winds in the mixed layer will reach 20-25 knots. Mixing will allow southwest gust to 25 mph. A cold front moves through during Wednesday night. Cold front approaching from the west brings a plume of precipitable water values around 1.1 inches. However most of this is distributed above 700 mb with dry air surface-to-850 mb. Confidence in showers is low, and so we maintain 15 to 30 pct pops with fropa. The front eventually stalls south of New England. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Active weather pattern for end of the week into the weekend * On and off precipitation with some wintry precip mix in * Dry weather next week Overview... Active pattern setting up across the region to close out the end of the week into the weekend. Stout subtropical high pressure over the Eastern Seaboard with longwave trough over the western CONUS. This high pressure will begin to break down and flatten as it retreats back towards Florida. This will drop the baroclinic zone back towards southern New England, and with several southern stream shortwaves, anticipate on and off again showers over the region. High PWAT airmass with Gulf Moisture connection especially over the weekend could lead to some river rises. A break down in the pattern early next week as ridging begins to build over the region. Details... Thursday & Thursday night...Moderate confidence. Passing cold front will drop south of the region early Thursday as surface high pressure moves into southeast Canada. This will put southern New England into a squeeze play with high pressure to the north and south, and stalled front draped across the region. Weak wave will move along the flow combined with increasing Gulf moisture will help produce showers across the region Thursday. Biggest question is thermals as a lot of guidance is cooling off during the day resulting in more snow than liquid precip. Model 2m temps are also cooling off leading to the idea of wet bulb temps as the precipitation moves through. Will continue with that trend in the forecast. Snowfall amounts do not appear to add to much as the ground will be quite warm thanks to 60 and 70 degree days during the mid week. High pressure will continue to slide through, pushing the baroclinic zone southward resulting in a break in the precip Thursday night. Temperatures will be back to seasonable. Friday into Saturday...Moderate confidence. Baroclinic zone still draped over or near the region as low pressure from the Midwest moves towards the Northeast. The stalled front over the region will transition as a warm front and will eventually lift northward towards northern New England. Pretty stout wave with southwest flow aloft pumping in Gulf moisture as PWATs increase to 2 STD above normal. While most of the precip should be in the form of rain, could see some thermal issues esp if warm air struggles to lift northward. So will continue to watch for freezing rain for the NW interior. In between this system and next, weak subsidence will move through resulting in a dry trend for the Saturday. Depending on the location of the front, the region should be more in the warm sector with highs in the 50s. Again this can change if the front moves farther north or slides a bit south. Thus lower confidence on temperatures profile. Saturday night into Sunday...Increasing confidence. Last of the multiple waves will move through the flow during this timeframe. Pacific southern wave will push through the southwest flow towards southern New England, drawing in more Gulf moisture. Surface low will develop and move across the southern Plains and into the Upper Great Lakes. This system`s cold front will swing into the area by Sunday bringing widespread rainfall. If temperatures are slow to warm could see a some wintry weather at the onset, but overall trend is towards rainfall. The front will quickly push through resulting in a drying trend for late Sunday night. Monday and beyond...Moderate confidence. Mid-level cold front will swing through resulting in strong CAA. High pressure will follow behind the front leading to dry weather and temperatures back to normal for late Feb. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...Moderate confidence. Tonight... Stratus and fog across Essex county and along the South Coast and Islands. The fog should eventually move out of the North Shore but expand across the southern half of the region. IFR and LIFR conditions in the fog area. Low level jet at 2000 feet shows winds near 40 knots, and may generate low level wind shear during the night. Wednesday... IFR/MVFR in fog and drizzle to start, improving to VFR by afternoon. SW gusts to 25 kt. Wednesday night... VFR through the night with scattered light showers. Brief MVFR cigs/vsbys possible in any showers. KBOS Terminal...Moderate confidence in TAF. Northeast winds should turn back to the south by 02-03z. May see low MVFR/IFR clouds during the morning push. KBDL Terminal...Moderate confidence in TAF. VFR conditions through early night. Conditions then lower to IFR after midnight. Conditions will improve to VFR Wednesday morning. Outlook /Thursday through Sunday/...Moderate confidence. Thursday: MVFR/IFR conditions possible. Breezy. SN likely, chance RA, chance FZRA. Thursday Night: Mainly VFR, with local IFR possible. Slight chance FZRA, slight chance SN. Friday: Mainly VFR, with areas MVFR possible. RA likely, chance FZRA. Friday Night: Mainly MVFR, with local IFR possible. RA likely, FZRA possible. Saturday: Mainly VFR, with areas MVFR possible. Slight chance RA. Saturday Night: Mainly MVFR, with areas VFR possible. Chance RA. Sunday: Mainly MVFR, with local IFR possible. Breezy. RA likely, FZRA possible. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. Southwest flow continues tonight through early Wednesday night. Strong winds aloft bring a potential for 20-25 knot gusts, strongest on the outer waters. Seas slowly build to 5-7 feet, mainly over the outer waters. Small Craft Advisory headlines will continue on some of the waters tonight through Wednesday night. Moist airmass moving over the cold water will continue to generate fog and low clouds, with areas of vsbys at or below 1/4 mile, mainly over the southern waters. A cold front moves through during Wednesday night and may bring widely scattered showers. Outlook /Thursday through Sunday/... Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain, chance of freezing rain, chance of snow. Local visibility 1 to 3 nm. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain, slight chance of freezing rain. Friday through Friday Night: Winds less than 25 kt. Rain likely. Saturday: Winds less than 25 kt. Slight chance of rain. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Sunday: Winds less than 25 kt. Areas of rough seas. Rain likely. && .CLIMATE... Record Highest Observed Temperature for February...(since records began) Boston.........73 (2/24/2017) Hartford.......73 (2/24/1985) Providence.....72 (2/24/1985) Worcester......69 (2/24/2017) Record High Temperatures... February.......2/20.......2/21 Boston.........68 (1930)* 63 (1906) Hartford.......69 (1930) 63 (1930) Providence.....69 (1930) 63 (1930) Worcester......65 (1930)* 59 (1930) * Records were broken today at BOS (70) and ORH (67) as of 400 PM Record Warmest Min Temperature... February.......2/20......2/21 Boston.........46 (1930) 45 (1994) Hartford.......50 (1981) 49 (1981) Providence.....48 (1981) 50 (1981) Worcester......47 (1981) 43 (2002) Extreme High Dew Points... Dew Point forecast has values in the 50s Today and Wednesday. February.......2/20......2/21 Boston.........54 (1991) 56 (1953) Hartford.......53 (1981) 55 (1989) Providence.....58 (1939) 56 (1989) Worcester......53 (1981) 54 (1953) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 8 AM EST Wednesday for MAZ020>022. Dense Fog Advisory until 10 AM EST Wednesday for MAZ023-024. RI...Dense Fog Advisory until 8 AM EST Wednesday for RIZ006-007. Dense Fog Advisory until 10 AM EST Wednesday for RIZ008. MARINE...Small Craft Advisory from 11 AM Wednesday to midnight EST Wednesday night for ANZ232>234. Small Craft Advisory from 11 AM to 9 PM EST Wednesday for ANZ231. Small Craft Advisory until midnight EST Wednesday night for ANZ235-237. Small Craft Advisory until 5 AM EST Thursday for ANZ250- 254>256. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...WTB/Dunten SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten CLIMATE...Staff

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