Area Forecast Discussion
Issued by NWS Boston, MA

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450 FXUS61 KBOX 161151 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 651 AM EST Thu Nov 16 2017 .SYNOPSIS... Wet weather overspreads the area this morning from west to east, followed by a brief period of heavy rain and gusty winds from late morning into early afternoon. Blustery winds follow the departing storm system tonight and Friday. Another round of showers will push across the region Saturday afternoon into early Sunday, with an isolated thunderstorm possible inland. Expect mild and blustery conditions in advance of the approaching cold front, followed by colder temperatures and continued brisk winds early next week. Dry conditions with temperatures near or below normal through the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 630 AM Update... Batch of showers moving across central and western areas as seen on latest NE regional 88D radar mosaic. Noting a N-S line of heavier showers from S of KALB into the NYC areas and NE coast of NJ, which has developed since 10Z. Line moving steadily NE. No lightning returns seen at this point, however. With temps in the lower-mid 30s across central and western portions of the Mohawk Valley/Route 2 corridor, would not be surprised to see a few more spotty reports of freezing or frozen precip with these areas before temps rise above freezing. Received a report of sleet earlier from Colrain in western Franklin county near the E slopes of the Berkshires. Winds as shifting to E-SE along the S coast of New England, with gusts up to around 20 kt at 11Z at KBDR and KHVN. Expect winds to continue to increase this morning. Have updated near term to bring conditions current. Previous Discussion... *** A brief period of heavy rain & isolated Thunder between 10 am and 4 pm from west to east with the low risk for localized strong wind gusts near the south coast *** Expect potent short wave to sweep across southern New England late this morning and afternoon, bringing a round of heavy showers, isolated T-storms and strong gusty winds to portions of the area. Parent low pressure moving across Ontario early this morning gives way to secondary/triple point low development south of New England later this morning. This is in response to strong forcing for ascent from approaching short wave trough. Mid level lapse rates steepen to about 7C/KM. This instability coupled with strong forcing will result in a period of heavy rain with embedded thunder from about 15Z-21Z from west to east across CT/MA/RI. Hi res guidance including the NCAR ensembles, ARW, NMMB and HREFv2 suggest rainfall totals of up to an inch is possible in a fairly short time period. This may result in minor poor drainage/street flooding, especially if elevated convection becomes more widespread. Other issue today will be the potential for strong winds. Secondary low/cyclogenesis is accompanied by an increasing low level SSE jet that clips the south coast including Cape Cod and the Islands from about 16Z-20Z. Greatest risk for strong winds will be in the warm sector, with model guidance suggesting this will be along the south coast including Cape Cod and the Islands. NAM most robust with strength of low level jet but also has some support from the remainder of the hi res guid. In addition, strong pressure rise-fall couplet across RI and southeast MA this afternoon will aid strong wind potential via enhancing isallobaric wind component. Furthermore heavy showers with embedded thunder and robust but shallow updrafts will further enhance wind threat across this region. Given these factors decided to hoist a wind advisory for the south coast. Day shift may need to consider expanding advisory into southern Bristol and Plymouth counties pending 12z model trends. As for convective threat, most of convection later this morning and afternoon appears elevated as core of warm sector and 50+ dew pt air remains offshore. So despite very high low level helicity values in vicinity of developing triple point low, SB instability likely gets shunted offshore. Nonetheless will have to monitor potential rotating storms near the south coast, but again likely remain offshore. As for temps, secondary/triple pt low development will trap low level cool air inland with highs only in the 40s. However farther south warm sector airmass clips south coast, Cape Cod and Islands where temps will climb into the 50s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight... Low pres over Gulf of ME continues to intensifies along with increasing CAA in its wake. The combination will result in windy and colder conditions tonight. NW winds 10-20 mph with gusts up to 35 mph over Cape Cod and the Islands. Temps will fall into the 30s but gusty NW winds will provide wind chills in the 20s. Friday... 987 mb low over the Maritimes continues to provide blustery NW winds across the region. Despite lots of sunshine highs will remain cooler than normal with temps 40-45 but wind chills in the 30s. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Showers expected late Saturday into midday Sunday * Gusty winds as a cold front moves across Sat night * Blustery and cold conditions early next week * Temperatures will run close to or below normal into the middle of next week Overview... Overall progressive mid and upper level steering flow continues across the northern hemisphere, with fast moving surface systems pushing across the region through the long term period. Expect temperatures to run mainly near or below seasonal normals, with brief readings a bit above ahead of the passing fronts. Strong low pressure moving across southern Quebec this weekend will bring another round of showers and blustery winds ahead and behind the quick moving cold front. Gusty northwest winds are likely into early next week, with wind advisories possible. Mainly dry conditions expected through the middle of next week with temps running close to or below normal. Details... Friday night... Deepening low pressure will push across the Gulf of Maine Fri evening. Tightening pressure gradient and cold air advection will bring blustery W-NW winds. Will see gusts up to 25-35 kt across the higher inland terrain and along the immediate coast through around midnight Fri night then will diminish as high pressure builds to the W. May also see leftover snow showers early across portion of the higher terrain of NW Mass. Expect temps to fall back to the 20s across most areas, except in the 30-35 degree range along the immediate coast. Saturday through Sunday... High pressure ridge progresses eastward as the center settles across the Carolinas during Saturday. NW winds will diminish, then shift to SW during the afternoon and begin to increase again ahead of next approaching system. There is some question on timing of onset of precip associated with approaching cold front. Have quickly increasing POPs during the day, though this will depend how fast the departing ridge moves E. Should see precip move in across most areas by around 21Z with increasing S-SW as well. Strong low pressure will cross central Quebec, with pressure down to around 980 hPa, while a secondary low forms as the occlusion moves across the region. May see SW wind gusts up to 35-40 kt Saturday evening, then will shift quickly to W as the cold front sweeps across May need Wind Advisory headlines for a time Sat night as gusts could approach 45-50 mph at times, highest along the S coast, Cape Cod and the islands. Back edge of precip should shift E Sunday morning, with drier air quickly working in. A few showers may linger into early afternoon across Cape Cod and the islands. Blustery W-NW winds continue with gusts up to 40-45 kt possible once again, so Wind headlines (Wind Advisory or even a few spots up to High Wind Warning criteria possible) may be needed again. Temps will start off close to normal, then will fall quickly by Sunday afternoon as colder air works in. May see a few lingering snow showers over parts of the E slopes of the Berkshires. Monday... A few snow showers may linger across the higher terrain of NW Mass through mid morning, otherwise expect dry conditions as high pressure sets up from W of Hudson Bay across the Great Lakes to the SE states. The tight pressure gradient between the departing low pressure across the Maritimes into Labrador and the high S and W of the region will keep temps up to 5 to 10 degrees below seasonal normals for late November. Highs will range from the 30s across the higher inland terrain to the lower 40s across the coastal plain. Tuesday and Wednesday... High pressure will progress E off the eastern seaboard on Tuesday as another weak, fast moving low moves across S central Canada. Will see a brief temperature rebound on Tuesday, close to normal readings as winds shift to SW ahead of the approaching front. However, most of the energy and moisture remains N of the region, so will remain dry for the majority of the region as it passes Tue night. Might see a few rain and/or snow showers across the E slopes of the Berkshires. Another high sets up across the central U.S. into central Canada Wednesday. More dry and cool conditions currently forecast. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...Moderate confidence. 1140Z update... Through Today... VFR conditions at 12Z will lower to MVFR from W-E with a period of IFR 15z-21z from west to east. Widespread showers with embedded downpours and isolated T-storms possible. Gusty SE winds up to 35-40 kt possible south coast including Cape Cod and Islands. A period of LLWS just to the north from PVD-BOS possible. High confidence on trends but remain uncertain on how much wind mixes down to the surface. Tonight... Any lingering MVFR in showers early quickly improves to VFR along with a wind shift from SW to NW with gusts of 25 to 30 knots. A few gusts up to 35 knots possible. High confidence. Friday...VFR, dry weather and NW winds 15-25 kt with a few gusts up to 30 kt possible. High confidence. KBOS Terminal...period of active weather 16z-20z with +SHRA and isolated -TSRA possible. LLWS likely south of Boston toward the Cape. KBDL weather 14z-17z with gusty +SHRA. Outlook /Friday Night through Monday/...Moderate to high confidence. Friday Night: VFR. Windy with local gusts to 30 kt. Saturday: VFR. Brisk. Chance SHRA. Saturday Night: Mainly MVFR, with areas VFR possible. Windy with gusts to 35 kt. SHRA. Sunday: Mainly VFR, with local MVFR possible. Windy with gusts to 35 kt. SHRA likely. Sunday Night and Monday: VFR. Windy with gusts to 30-35 kt. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...Moderate confidence. Today... Low pres develops south of New England this morning then intensifies as it moves onshore into RI/southeast MA this afternoon, then emerges over the Gulf of ME this evening. SE gales likely and then becoming SW late. Heavy showers and embedded thunder will limit vsby. Low probability of an isolated waterspout around the islands and offshore. Tonight and Friday... Low pressure over Gulf of ME tonight heads into the Maritimes Fri and provides near gale force NW winds. Dry weather and NW winds provide good vsby. Outlook /Friday Night through Monday/...Moderate confidence. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Saturday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas locally approaching 5 ft. Saturday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Rain showers likely. Sunday and Sunday night: Moderate risk for gale force winds with gusts up to 35 kt. Rough seas up to 15 ft on the outer waters. Rain showers likely Sunday. Monday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Wind Advisory from 10 AM this morning to 8 PM EST this evening for MAZ020>024. RI...Wind Advisory from 10 AM this morning to 8 PM EST this evening for RIZ006>008. MARINE...Gale Warning from 11 AM this morning to 4 PM EST Friday for ANZ231>235-237-254>256. Small Craft Advisory from noon today to 5 PM EST Friday for ANZ230. Gale Warning from 11 AM this morning to 7 PM EST this evening for ANZ236. Gale Warning from 7 PM this evening to 4 PM EST Friday for ANZ250-251. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera/EVT SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.