Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 190926 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 426 AM EST Sun Nov 19 2017 .SYNOPSIS... Strengthening low pressure over western NY state at predawn continues to intensify as it moves across northern New England this afternoon. Its attending cold front sweeps through the region late this morning into early afternoon. Behind the front, mild air this morning is replaced by much colder weather on blustery west winds this afternoon into Monday. Turning mild again Tue as high pressure moves offshore. A cold sweeps across the region early Wed along with a few showers. High pressure brings dry but colder weather into New England Thanksgiving Day and continues into Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 4 AM update... *** Strong Southwest Winds Along The South Coast This Morning Followed By Strong West Winds This Afternoon All Areas *** This Morning... 983 mb low over western NY at 4 am and will continue to intensify as mid level short wave approaching from the west takes on a negative tilt. Strong 130 kt upper level jet streak associated with this feature with its LFQ overspreading southern New England this morning, enhancing QG forcing. This combined with a plume of subtropical PWATs of 1.5 inches (+2 STD) will yield in some locally heavy downpours. Some support from 00z meso guidance that a broken fine line of low top convection may try to develop along and ahead of the approaching cold front from about 10z-15z. Dew pts rising into the mid and upper 50s this morning providing a few hundred joules of SB cape. Thus could be enough instability coupled with the very strong forcing for ascent to yield some embedded convective elements. These heavier showers may transport strong winds aloft down to the surface. Greatest risk of this occurring will be along the south coast, Cape Cod and Islands where core of low level jet traverses this morning. Low level jet (925 mb) peaks at 60-65 kt around 12z, however model soundings indicate steep inversion precluding much mixing and will likely keep winds below High Wind Warning criteria. Thus after collaboration with OKX High Wind Warnings for south coastal MA/RI and coastal CT will be downgraded to wind advisory. Thus thinking wind damage will not be widespread but rather more localized. At 4 am highest wind gusts so far 37 kt at EWB. So capped gusts to about 45 kt and sustained to 25-30 kt. As for temperatures, impressive thermal advection ahead of the approaching cold front into southern New England with 4 am temps in the low 60s across RI and southeast MA! Shallow cool air in the CT river valley finally getting scoured out by heavier showers. Rainfall amounts will average 0.25 to 0.50 inches but could locally have amounts up to 0.75 inches in heavier downpours given PWATs up to 1.5 inches. Not expecting any flood issues. This Afternoon... Strong cold front moving offshore around midday. Intensifying 979 mb low over ME will provide strong pres gradient and combine with CAA to steepen low level lapse rates and good pres rise-fall couplet to support WNW post frontal winds up to 40 kt. Thus will continue wind advisories for the entire region, as there could be isolated wind damage behind the front. Morning clouds and showers will give way to partial afternoon sunshine with temps falling behind the front. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... 4 AM update... Tonight... Chilly night with good CAA as 850 mb temps drop to about -10C by 12z Monday. Lows in the 30s with 20s inland but will feel much colder given gusty WNW winds. Other issue will be potential lake effect snow showers from NY state moving into western MA/CT and possibly RI. All mesoscale guid advects low level moisture from the lakes and steepening low level lapse rates into the region. Will have to monitor later model trends to be more specific on these potential mesoscale snow bands. For now just inserted slight chance pops into the forecast. && .LONG TERM /MONDAY THROUGH SATURDAY/... */ Highlights... - Blustery NW winds on Monday - Moderating temperatures Tuesday and into Wednesday - Dry but chilly for Thanksgiving day */ Pattern Overview/Confidence... Building high pressure over Baja California will push the ridge into the Western CONUS for next week. This will keep the eastern half of the country in a trough til perhaps the end of the week. Overall 12z guidance is in general agreement, however guidance spread occurs with each potential shortwave and frontal systems that pass through. Trended the forecast towards the UKMET and 12z EC as the GFS appears to be too robust within this pattern set-up, esp towards the end of the week. Details... Monday into Tuesday...High confidence. Cold airmass continues to remain overhead on Monday as high pressure to the south begins to build. Departing shortwave from the north will increase the pressure gradient and thus anticipate gusty westerly winds to continue during the day. Anticipate a mostly dry day, but could see ocean effect showers across the open waters. Mid-level ridge will pass through overnight into Tuesday as winds switch and WAA returns across southern New England. Temperatures will warm within this southwesterly wind as 50`s return back to the region. Approaching cold front from the west will result in a developing LLJ with 925mb winds reaching 40-45 kts. Once again another windy evening for Tuesday. Wednesday into Thanksgiving...Moderate confidence. Approaching cold front from the Great Lakes will result in a mild start on Wednesday. Depending on the available moisture, scattered showers may develop along and/or ahead of the front. Both the EC and CMC have continued to show precip chances while the GFS keeps the bulk of the moisture offshore. Will continue to ride with chc pops until guidance spread decreases. Behind the front, CAA will move back into the region for Thursday. Continue with the dry trend for the later half of the day as the 12z GFS deterministic run appears to be an outlier with its developing coastal low. Most of the GEFS also keeps the developing low well offshore like the CMC. This developing low is also not supported by the UKMET or the EC. Therefore anticipate a chilly day as temps fall below seasonable with dry conditions. Friday and beyond...Increasing confidence. Increasing cloud cover overnight as secondary cold front swings through. However, temps will begin to moderate as pattern turns a bit more zonal. A few shortwaves will push through next weekend but timing and exact impact remain uncertain at this time. && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... 1 AM Update... Thru 17z/Noon... Widespread MVFR with areas of IFR across the interior in showers with embedded heavy downpours. Strongest/gusty SSW winds 09z-16z from west to east along the south coast of MA/RI. Strongest winds may occur in these heavy downpours. Elsewhere, LLWS thru 15z-16z, then low level jet moves offshore. After 17z... Cold front exits the area with a wind shift from SSW to WNW with gusts up to 40 kt. Any leftover MVFR at midday will quickly improve to VFR and dry weather. The only exception may be in the hills of western MA/CT where MVFR is possible behind the front. Tonight... VFR cigs SCT-BKN040 with possible -SHSN from Lake Effect snow showers coming across NY state into western MA/CT and possibly RI. WNW winds will remain gusty up to 35 kt. KBOS Terminal... MVFR with periods of showers, embedded heavier downpours thru about 16z. SSW winds may briefly gusts up to 40 kt in the heavier showers. LLWS til 16z then becoming VFR as a cold front sweeps across the terminal with a wind shift from SSW to WNW with gusts up to 40 kt. KBDL Terminal... Mainly IFR but trending toward MVFR. Periods of showers with locally heavy downpours. Light winds becoming SSW toward daybreak. Although winds may become gusty in heavier showers. Strong cold frontal passage around 15z with wind shift from SSW to WNW. MVFR improving to VFR with the wind shift. Outlook /Monday through Thursday/... Monday: VFR. Windy with gusts to 35 kt. Monday Night through Tuesday: VFR. Windy with gusts to 30 kt. Tuesday Night: Mainly VFR, with local MVFR possible. Windy with gusts to 30 kt. Chance SHRA. Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA. Wednesday Night: VFR. Breezy. Thanksgiving Day: VFR. && .MARINE... This morning... SSW gales except storm force winds south coastal waters of MA/RI. Heavy showers and fog will result in poor vsby at times. This Afternoon... WNW gales all waters behind cold front which crosses the waters late this morning into early afternoon. Improving vsbys with the wind shift. Tonight... WNW gales continue much of the night. Mainly dry weather but rain/snow showers well offshore. Outlook /Monday Night through Thursday/... Monday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 11 ft. Monday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Tuesday: Low risk for gale force winds with gusts up to 35 kt. Local rough seas. Tuesday Night: Low risk for gale force winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers. Wednesday: Winds less than 25 kt. Local rough seas. Chance of rain showers. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thanksgiving Day: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory from noon today to 10 PM EST this evening for CTZ002>004. MA...Wind Advisory until 10 PM EST this evening for MAZ017>024. Wind Advisory from noon today to 10 PM EST this evening for MAZ002>016-026. RI...Wind Advisory until 10 PM EST this evening for RIZ002>004- 006>008. Wind Advisory from noon today to 10 PM EST this evening for RIZ001. MARINE...Storm Warning until 10 AM EST this morning for ANZ232>234. Gale Warning until 10 PM EST this evening for ANZ230-236. Gale Warning until 6 AM EST Monday for ANZ231-250-251-254. Storm Warning until noon EST today for ANZ235-237-255-256. && $$ SYNOPSIS...Nocera NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...Dunten/Correia AVIATION...Nocera/Dunten/Correia MARINE...Nocera/Dunten/Correia

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