Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201822 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 122 PM EST Tue Feb 20 2018 .SYNOPSIS... A mild southwest flow will bring unseasonably mild temperatures this afternoon, with record warmth possible Wednesday. A cold front moves through Wednesday night followed by much 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 PM THIS EVENING/... Dense Fog advisory was extended to 11 AM on the RI coast and the Islands. Visibility had lingered at 1/4 to 1/2 mile in this area, but was moving up to 3/4 mile at Newport so there is reason to expect the advisory will wind down soon...if not 11 AM then sometime around the midday. Depending on observations near 11 AM, we may extend the fog headline into early afternoon. 12Z NAM cross sections show surface moisture thinning over the interior, but with patches of higher RH values 850-900 mb. Satellite imagery shows low clouds across much of CT-RI-SE Mass late morning with patchy low and mid level clouds farther west. Based on this we continue to expect a clearing trend across northern Mass, and possibly across parts of northern CT, northern RI and interior SE Mass. South coast should lose much of the fog, but the clouds may linger due to southwest winds moving moist air...dewpts 50-52...over the ocean and then onshore. Where skies have been clearing, temperatures have climbed to the mid to upper 50s. The hourly temperature grids at several sites on the North and South Shores were 2-4F milder than earlier forecast. We nudged max temps up a few degrees in those areas. Low clouds and lingering fog and a wind off the ocean will keep the South Coast areas around 50 or the low 50s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... Mild SW flow continues tonight. Abundant low level moisture will lead to areas of stratus and fog redeveloping, most prevalent along the south coast. Dry air in the mid levels so patchy drizzle possible. Temps may remain at or above 50 degrees tonight, except 40s Cape/Islands and immediate south coast. Wednesday... Persistent SW flow continues ahead of approaching cold front. Areas of stratus and fog expected to burn off with at least partial sunshine developing by afternoon. Soundings indicate slightly deeper mixing than today, up to 925 mb where temps 15-16C. With full sunshine, potential would exist for low to mid 70s in the interior. However, low clouds expected to linger through the morning which may limit full potential so expected highs upper 60s to lower 70s away from the south coast which would still comfortably establish record highs at BOS,BDL,ORH and close call at PVD. These temps are up to 30 degrees above normal. SW flow with gusts to 25 mph will keep temps in the 50s along the immediate south coast. Cold front approaching from the west may bring a few late day showers to western MA. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... */ Highlights... - Showers Wednesday night - Cold rain, wet snowflakes Thursday - Active weather pattern Friday through the weekend - Watching for potential mixed precipitation, freezing rain - Pattern change early next week */ Overview... Persistent SE CONUS sub-tropical H5 ridge maintained by parked N- Central Pacific split flow and downstream H5 trof over the W CONUS generating a warm-moist atmospheric river from the Central Pacific NE to SE Canada. But nothing lasts forever. Breakdown of upstream pattern, thermal wind flattens through which impulses stretch, dip southward. A brief midweek warm-up is followed by an active weather pattern late week into the following week. Along a parent frontal / baroclinic zone, sulked S, stretching across the NE CONUS, thermal profiles in question as intriguingly ensembles signal an evolving blocky N Atlantic pattern per forecast strong -NAO into March. Will hit on targets of opportunity below. Ensemble guidance preferred. */ Discussion... Wednesday night into Thursday... Leaning with the cold front pushing S, suppressed via high pressure, sinking mid-level air. Showers overnight. Attention turns to a wave ejecting along the baroclinic zone into Thursday. Daytime event, 2m temperatures wavering around 34. An over-running event, perhaps some vertically-staggered W-E banding pressed up against the 1040+ high, as cool, dry air undercuts. Expect a cold rain event, wet snowflakes mixed in, but no accumulation. More activity/outcomes closer to the S-coast of New England. Thursday night... Hold with an influential near 1040 high and hold off on any weather. With that, light winds, mostly clear conditions, favor radiational cooling and will lean towards cooler 2m temperature guidance. Friday into Friday night... Lifting warm frontal disturbance with surface high pressure settled to the E. Noting ageostrophic wind profiles, wet-bulb temperatures, low level thermal profiles, will be monitoring for potential shallow cold air to lock-up briefly across N/W MA especially within interior sheltered valleys. Can`t rule out a short period of freezing rain, confidence gained via CIPS analogs. Otherwise rain and warming temperatures, non-diurnal trend during the overnight period. Saturday into Sunday... More potent CONUS disturbance ahead of which high pressure builds over E Canada. Will be monitoring for precipitation-type issues once again with the possibility of a near-shore secondary low developing despite the thrust of stronger dynamics N/W across the Great Lakes Region. Beyond 120 hours, notable ensemble member spread, confidence low at this time. CIPS analogs indicate freezing rain, mainly N/W MA per a top analog from early February 2008. Snows further N/W. Early next week... Perhaps a breather before the pattern begins to change as noted in the OVERVIEW section above. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...Moderate confidence. This afternoon... VFR most inland places. lINGERING IFR/LIFR cigs and vsbys along the South Coast of RI and Mass will slowly improve, but expect IFR or low-end MVFR cigs to linger there through the afternoon. SW winds with gusts up to 20 to 25 kts especially over SE areas of New England. Tonight... Stratus and patchy fog redeveloping with IFR conditions. Areas of LIFR along the south coast. Patchy drizzle. 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. VFR conditions through early tonight. LLWS threat tonight. Guidence is insisting on bringing BOS to 1/4 mile vsby and 100 foot ceiling, but that rarely happens with a southwest wind, which is expected tonight. We compromised with an 800 foot ceiling, which is the source of the moderate confidence. Conditions improve to VFR Wednesday morning. KBDL Terminal...Moderate confidence in TAF. VFR conditions through early night. Conditions then lower to LIFR after midnight. The source of the moderate confidence comes from timing uncertainty as well as concerns the conditions may just lower to IFR. Conditions will improve to VFR Wednesday morning. Outlook /Thursday through Saturday/...Moderate confidence. Thursday: VFR. Chance RA, chance SN. Thursday Night: VFR. Slight chance RA, slight chance FZRA, slight chance SN, slight chance PL. Friday: VFR. Chance RA, chance FZRA, chance PL. Friday Night: MVFR/IFR conditions possible. Chance RA, chance FZRA, patchy BR. Saturday: Mainly VFR, with local MVFR possible. Chance RA.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Persistent SW flow. Modest low level jet over the waters through Wed but strong inversion will prevent winds from mixing down. Expect gusts mostly below SCA but up to 20kt at times. Poor vsbys in fog expected for most of the period, mainly over south coastal waters. Outlook /Wednesday Night through Saturday/... Wednesday: Winds less than 25 kt. Seas up to 5 ft. Areas fog. Local visibility 1 nm or less. Wednesday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain. Thursday Night: Winds less than 25 kt. Chance of rain, slight chance of freezing rain. Friday: Winds less than 25 kt. Chance of rain, chance of freezing rain. Friday Night: Winds less than 25 kt. Chance of rain. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. && .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) 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...
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CT...None. MA...Dense Fog Advisory until 2 PM EST this afternoon for MAZ023- 024. RI...Dense Fog Advisory until 2 PM EST this afternoon for RIZ006>008. MARINE...Small Craft Advisory from 7 PM this evening to 7 PM EST Wednesday for ANZ235. Small Craft Advisory until 7 PM EST Wednesday for ANZ250- 254>256.
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&& $$ SYNOPSIS...KJC/Sipprell NEAR TERM...WTB SHORT TERM...KJC LONG TERM...Sipprell AVIATION...WTB/KJC/Sipprell MARINE...WTB/KJC/Sipprell CLIMATE...

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