Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201806 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 206 PM EDT Mon Mar 20 2017 .SYNOPSIS... Departing ocean storm will result in some lingering clouds and gusty winds over the Cape and Islands this morning, otherwise high pressure building in from the west will result in diminishing wind, sunshine and milder temperatures this afternoon continuing into Tuesday. An arctic front will bring near record cold Wednesday and Thursday along with bitterly cold wind chills. A warming trend then develops Friday into Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1020 AM update... Ocean storm slowly pulling away with ridging and subsidence building in behind it. Back edge of cloud shield will be exiting Nantucket next few hours, otherwise, lots of sunshine expected with just a few high clouds moving in from the west. Gusty winds along the coast will slowly subside. Sunshine combined with northerly winds backing to the northwest will push afternoon temps into the upper 40s and lower 50s, cooler Cape/Islands which is a few degs warmer than normal. Should note that it`ll feel cooler along the immediate E shore of MA and across the Cape and Islands with breezy N winds. The usherance of colder air off the waters combined with winds will make the real-feel temperature around the upper 30s to low 40s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight... Continued quiet and dry weather with mild conditions aloft. Toss up, dewpoints are still low as the dry mass still lingers, yet scattered to broken cloud decks are forecast to build across the region ahead of a weak diffuse cold frontal boundary sweeping the area. Light winds overall. So which will be the greater influence of overnight lows? Will lean with dry dewpoints and radiational cooling. Lows down into the upper 20s to low 30s, with notorious locations known for dropping out likely falling into the low to mid 20s, for example Norwood and Taunton airport, interior valleys of N/W MA. Tuesday... Mix of sun and clouds, perhaps more clouds at times, but overall quiet weather. A light chance of showers up along the W slopes of high terrain up against a weak diffuse cold frontal boundary. Other- wise another mild day, highs into the low to mid 50s with slightly higher dewpoints. Should see a bit more snowmelt across the region. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Arctic blast with near record cold Wednesday and Thursday * Warming trend Friday and Saturday with some showers likely Daily Details... Tuesday night... An arctic cold front sweeps across the region late Tue night. Frontal passage looks dry with the probability of any snow showers/squalls very low given models offering very little moisture, instability or low level moisture. Wednesday and Thursday... Arctic airmass remains on track with impressive cold air advection across the region Wed as 850 temps lower to -18C to -20C and -16C at 925 mb! Very anomalous airmass for late March with temperature anomalies down to -2 standard deviations colder than climo. Given this temps were derived from the coldest guidance sources. Gusty northwest winds coupled with the frigid airmass Wed, Wed night and possibly into Thu morning will yield bitterly cold wind chills. Very harsh conditions for anyone outdoors for an extended period of time. In fact this airmass is so anomalous record lows Wed ngt/Thu morning may be challenged with lows in the single digits and teens! See climate section below for details. Very cold start to the day Thursday. Late March sun angle will go to work on cold airmass but will be limited as 1036 mb high nearby will limit blyr mixing. Thus shallow cold air will be difficult to modify much. Hence another cold day with highs only in the 30s. However a modest WNW wind will likely keep wind chill values in the single digits. Friday... This will be our transition day as the Arctic high moves offshore and warm advection pattern begins to overspread our region. This change in regime will be accompanied by an increase in cloud cover, milder temps but also the risk of some precip. Temps likely climbing into the 40s to perhaps near 50 in spots. Next Weekend... Both GEFS and Euro ensembles along with deterministic guidance in good agreement that warm sector likely overspreads southern New England Fri night into Saturday. GEFS suggest 925 and 850 mb temp anomalies around +1C. This combined with SW surface flow should support highs well into the 50s to possible 60s away from the south coast. Wild card here is what previous forecaster alluded to, a fairly baroclinic zone/front across northern New England is poised to slide south with height falls from approaching mid level trough. Thus tricky temp forecast Sat pending timing of fropa. This frontal boundary will be accompanied by modest moisture with GEFS ensembles indicating PWATs +1 standard deviations above normal. So risk of showers with this frontal boundary late Sat/Sat night. Moving forward into Sunday forecast becomes more complex as Arctic high advects southward from Ontario into southern Quebec and as its shallow cold airmass advances southward precip may changeover to a wintry mix as previous forecaster noted. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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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 Tuesday night/... Through 00z...VFR. N/NW gusts 20-30 kt Cape/Islands diminishing. Tonight into Tuesday...High confidence. VFR cigs with mid/high clouds moving in tonight. Lower VFR cigs Tue with patchy MVFR and a low risk of a brief shower, mainly interior. Tuesday night...High confidence. Mainly VFR but a few snow showers possible late along an arctic front, mainly over the Berkshires and western MA. Increasing NW winds with gusts to 20-30 kt developing 09-12z. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Wednesday through Friday/... Wed and Thu...High confidence. Mainly VFR, dry weather and NW Winds gusting 20-30 kt then diminishing Thu afternoon. Fri...Moderate confidence. Winds shift to the SW. Mainly VFR, but a MVFR CIGS may begin to filter in from the S late in the day. Low risk for a period of rain late Fri/Fri night with warm front.
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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 Tuesday/... Winds and seas will continue to diminish. Will see gales linger on the SE waters into the morning period, then 25 to 30 kt N gusts throughout the day. With high pressure building into the waters, winds diminishing, will see wave action initially 8 to 12 feet this morning drop off into Tuesday morning. Quiet boating weather otherwise. Outlook /Tuesday Night through Friday/... Tue night...high confidence. Arctic front moves across the region late toward daybreak Wed with wind shift to the NW and speeds 20-30 kt. Wed and Wed night...Moderate confidence. NW winds with gusts potentially reaching 35 kt. Given arctic airmass combined with gusty NW winds and wave action, light to moderate freezing spray possible especially Wed night. Thu...High confidence. Mainly quiet boating weather after winds and seas recede early. Fri...Low confidence. Winds shift to the SW. May reach 35 kt by Fri afternoon, but more likely small craft advisories may be needed. Timing somewhat uncertain. && .CLIMATE... Record cold highs for Wednesday, March 22nd are below: Boston (BOS) 24/1885 Hartford (BDL) 29/1960 Providence (PVD) 28/1914 Worcester (ORH) 25/2002 BDL and ORH will be within a degree or two of these record cold highs Wednesday. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ230- 232-235>237. Small Craft Advisory until 11 PM EDT this evening for ANZ233- 234. Small Craft Advisory until 11 AM EDT Tuesday for ANZ231-251. Small Craft Advisory until 5 PM EDT Tuesday for ANZ250-254. Small Craft Advisory until 8 PM EDT this evening for ANZ255- 256. && $$ SYNOPSIS...Nocera/Sipprell NEAR TERM...KJC/Sipprell SHORT TERM...Sipprell LONG TERM...Nocera AVIATION...KJC/Nocera MARINE...Nocera/Sipprell CLIMATE...

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