Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191152 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 652 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, the mild air will be replaced by much colder weather on blustery west winds this afternoon into Monday. Winds shift to southwest with milder temperatures on Tuesday, followed by a cold front sweeping across the region that will bring showers late Tuesday night and Wednesday morning. Dry and colder conditions expected late Wednesday through the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 630 AM Update... Area of showers with some heavier downpours moving across the region as seen on latest NE regional 88D radar imagery. While the area moves slowly E, elements with the area are pushing steadily NE. Noting a few clusters of lightning well S of Long Island, but not lasting very long as they shift along with the rain. Very mild this morning on the gusty S-SW winds. Readings at 11Z include 62 degrees at KPYM and KHYA and 61 at KMVY, OWD and PVC. Will either remain in the mid 50s to lower 60s across the coastal plain or rise another degree or two before starting to fall later this morning as the cold front moves across. Further inland, temps mainly in the lower-mid 50s with a few spots still below 50. Stronger winds aloft may mix down with some of the heavier rainfall especially across S coastal areas. Have updated near term to bring conditions current, but not terribly far off except for temps inland, but has been tough to scour out the cold low level temps. Previous Discussion... *** 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 through 15z. Dewpts 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. 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... * Dry conditions and blustery NW winds Monday * Moderating temperatures Tuesday into early Wednesday * Dry but chilly for Thanksgiving day and Friday Overview... Overall progressive mid level pattern continues across North America through most of the long term period, with a few fast moving H5 short waves in the northern stream flow. There may be scattered showers with milder temperatures ahead of the short wave and surface frontal passages, followed by colder temps and some gusty winds especially on Monday. May see some amplification of the mid level flow across the eastern half of the U.S. around mid week, which continues to show some signs of model solution spread giving a bit lower confidence in timing the surface front through. Models in better agreement in bringing some southern stream moisture up the eastern seaboard as cold front approaches around the Wednesday timeframe. The front remains progressive, and should push offshore Wed night, just in time for dry but cooler conditions for the Thanksgiving day HS football games. Temps look to remain on the cool side at the end of the week. Details... Monday into Tuesday...High confidence. Another weak disturbance in the W-NW flow should remain dry but will bring colder air across the region as it moves through the northern extent of the large high pressure are settling across the southern Appalachians and SE U.S. on Monday. May see some lake effect snow shower streamers try to cross the Berkshires into western areas, mainly near the E slopes and the northern CT Valley especially late morning into the early evening hours. At this point, should see only light activity. Not expecting temps to recover much during the day with W-NW winds gusting up to 30-40 mph, highest across the higher terrain and east coastal areas through midday, then should slowly diminish. Excellent cold air advection with H85 temps down to -10C to -12C through midday with little change in the afternoon. Expect highs only in the lower-mid 30s across the higher terrain ranging to the lower 40s along the immediate coast. NW flow early Tuesday will back to SW as the large high pressure center shifts E during the day. Will see return of milder temps as readings top off in the mid 40s to mid 50s, with a few upper 50 degree readings possible across S coastal areas. A cold front will approach late in the day but will remain dry. Tuesday night and Wednesday...Moderate confidence. Expect the cold front to push quickly across, but most of the energy and moisture will remain across northern New England into southern Quebec. Good pressure gradient sets up between the high exiting to the E and the approaching front. Plus, models continue to signal moisture working up the eastern seaboard from developing southern stream mid level system across S GA/FL into the eastern Gulf of Mexico. Still some timing issues amongst the model suite, but showing a bit better continuity in bringing precip across most areas except N central and NW Mass Tue night, then will push E Wed. May see a decent shot of QPF amounts during Wed as the moisture feed moves across eastern areas with 0.2 to 0.3 inches possible before ending. Kept CHC POPs going, with best chances across S coastal areas. High temps Wed will top off a few degrees either side of seasonal normals. Winds shift to W as the front exits late Wed into Wed night, bringing yet another shot of colder air from central Canada. Thanksgiving and Friday...Moderate to high confidence. High pressure sets up from New England southwestward through the Ohio Valley into the mid Mississippi Valley by midday Thanksgiving day, then slowly shifts S Thu night and Friday. Models trying to bring another low toward the region from Manitoba and western Ontario late Friday, but model solution spread on timing and track of this system. Have kept a dry but cold forecast going through Black Friday. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... 650 AM Update... Thru 17z/Noon... Widespread MVFR with areas of IFR across the interior in showers with embedded heavy downpours. Strongest/gusty SSW winds moving from W-E along the south coast of MA/RI. Strongest winds may occur in these heavy downpours. Elsewhere, LLWS with SW winds at 50-55 kt up to 2Kft 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: VFR. Windy with local gusts to 30 kt. Chance SHRA. Wednesday: VFR. Chance SHRA. Wednesday Night: VFR. Breezy. Thanksgiving Day: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... 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 through Thursday/... Moderate to high confidence. Monday: Moderate risk for gale force winds with gusts up to 35 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: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Wednesday Night through Thanksgiving Day: Winds less than 25 kt. Areas of seas approaching 5 ft. && .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>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/EVT NEAR TERM...Nocera/EVT SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT

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