Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 290259 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 959 PM EST Mon Nov 28 2016 .SYNOPSIS... An approaching warm front will allow rain to overspread the region Tuesday morning, which may become heavy at times south of the Massachusetts turnpike Tuesday afternoon and early evening. A brief period of drying will occur late Tuesday night into part of Wednesday morning, but another period of rain heavy at times will occur Wednesday afternoon and night as low pressure moves into New England. Improving conditions Thursday as the low moves into the Maritimes with mainly dry and cooler weather for Friday through Sunday. && .NEAR TERM /UNTIL 4 AM TUESDAY MORNING/...
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10 PM Update... New 00z NAM/MET guidance continues the risk for a few hours of freezing rain Tue morning across northwest MA from about 10z to 14z before surface temps rise above freezing. 00z NAM qpf across eastern OH ending at 03z appears to be on track when compared to surface observations. NAM brings this qpf into northwest MA around 12z. In addition 00z MET guid temps at 03z across southern New England appear too warm when compared to 03z obs. Thus NAM/MET surface temps running too warm and with that said still has subfreezing temps at 12z across northwest MA. Hence increased forecast confidence in freezing rain advisory especially western portions of MA. Therefore will continue with advisory and monitor latest observations thru the night along with the remainder of 00z guid for any changes to configuration of advisory. Otherwise previous forecast remains on track. Previous discussion follows... Light winds and mostly clear skies into a good chunk of this evening will allow temps to quickly fall after sunset. Clouds will then increase from west to east, particularly after midnight ahead of an approaching low pressure system. Most locations should see low temps drop into the upper 20s to the lower 30s, with even some middle 20s across the normally coolest outlying locations. These low temps will likely occur near or shortly after midnight. Temps should then level off or rise a few degrees as clouds increase as well as thicken. Dry weather should prevail through 4 am.
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&& .SHORT TERM /4 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... * Brief period of freezing rain possible across interior northern MA between 5 and 9 am Tue morning * Rain overspreads the region Tue am and may be heavy for a time during the afternoon/early evening south of the MA Pike * Areas of fog may be locally dense late Tue night/early Wed am Wave of low pressure approaches from the southwest Tuesday morning increasing the forcing for ascent. Guidance appears to hint an initial band of precipitation that may sweep through our western and northern zones between 5 and 9 am in the warm air advection pattern. It is uncertain how much of this precipitation will reach the ground, but concerned for the risk for a brief period of light freezing rain with this activity. Most of the raw 2 meter temperature guidance shows readings above freezing during this time frame. However, noticed that MOS guidance had virtually no wind with temps near or just below freezing around 12z which has us concerned. The raw guidance may end up a few degrees too mild in this scenario, given little wind to scour out boundary layer cold. So despite the uncertainty, opted to issue a short-fused Freezing Rain Advisory for northwest/north central MA given the potential impacts just a small amount of light freezing rain often has on roads/walkways. Confidence is not as high as we would like for a short term forecast, but the timing near rush hour certainly increases the concern. It is possible that we luck out and temps are already above freezing by the time precipitation arrives. On the flip side of the coin, if activity arrives earlier than expected, we may even need to extend the advisory a bit further south and east. Certainly no issues on the coastal plain, as rain overspread the region Tuesday morning. An impressive 50 to 60 knot southerly low level jet develops by Tue afternoon, coupled with PWATS 2+ standard deviations above normal for this time of year. With that said, expect a soaking rainfall Tuesday afternoon/early evening. The rain may be heavy at times, south of the Pike where low level jet intersects wave of low pressure tracking across the region. In fact, a rumble or two of thunder certainly can not be ruled out across RI/southeast MA along with brief nuisance poor drainage street flooding. Rainfall from this first event should average between 0.50 to 1.25 inches, but localized 2 inch amounts are certainly possible in any convection with the highest risk for this across CT/RI/SE MA. The bulk of the rain should be over by late Tuesday evening, with dry weather prevailing overnight. Biggest concern will then be for areas of fog developing, which may become locally dense in the typically prone locations where winds decouple. Temps are tricky Tuesday afternoon and night. Much of the region should eventually warm sector, but may take until Tue evening, when highs reach between 55 and 60 south of route 2 in MA. North of route 2, it is possible that temps remain below 50 as that area may never warm sector. Lows by daybreak Wed should mainly be in the upper 30s to the middle 40s in most locations. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * More rain, heavy at times Wed afternoon and night * Improving conditions Thu with cool and blustery weather Fri through the weekend * Uncertainty for Sunday night/Monday regarding potential for another low pressure system Overview... High amplitude longwave trof with closed low initially centered over the Great Lakes Region will contribute to another round of soaking rainfall for southern New England during Wed/Wed night. Continue to expect more of a split flow pattern by the end of this week and this weekend, with low amplitude northern stream across the Gt Lakes and NE. This will bring mainly dry and cooler weather for late this week and into this weekend, but series of fast moving shortwaves move through the flow so can`t rule out brief rain/snow showers at times but timing uncertain. Greater uncertainty exists for Sunday night/Monday regarding potential for an upper trof advancing from the west. Details... Wednesday into Wednesday night... Wednesday looking dry to start, may even have some breaks of sunshine initially, but then through the morning and the course of the day we see steadily increasing moisture as another wave of low pressure heads our way from the southwest. This results in a quick increase in cloud cover and rain developing for the afternoon. Precipitable water increases to 1 to 1.5 inches, accompanied by a SW low level jet and divergence aloft. Continue to think that the majority of the rainfall from this event will occur during Wed afternoon and evening, close to timing of when low level jet works its way into our region. Another soaker anticipated with the potential for 0.75 to 1.5" of rainfall, possibly localized totals of around 2". Area rivers and streams should be able to handle this second round of rainfall, though some street flooding could occur with any leaf-clogged drains. Highs Wed will be dependent on how far north warm front gets. Best chance of temps reaching the upper 50s continues to be along south coastal MA and RI, since front may get hung up south of the Mass Pike for this event. Cooler upper 40s to possibly low 50s likely further to the north across northern MA and possibly over part of northern CT. South of the front models indicate some modest instability which is accompanied by decent lift, so can`t rule out rumbles of thunder. Surface low deepens some as it traverses our area, but should start pushing NE of our region towards 12Z. Rainfall dwindles after midnight. Thursday... Low pres in the Gulf of Maine will lift NE into the Maritimes with drier westerly flow into SNE. With mid level trof axis still to the west and shortwaves rotating through, can`t rule out a brief rain shower, especially in the vicinity of the east slopes of the Berkshires. But by midday moisture becomes quite limited. Anticipating some diurnal stratocumulus clouds with partly to mostly sunny skies. While it is cooling aloft, low level temps are fairly mild so temps should reach well into 50s in the coastal plain with upper 40s interior high terrain. Friday through Sunday... Mainly dry, cooler and blustery conditions with westerly flow as broad trof settles in over the NE. Still a few shortwaves rotating through the flow and weak surface low passes thru northern New England on Fri, so a low risk for a brief rain/snow shower, mainly interior high terrain. Seasonable temps Fri cooling a bit below normal next weekend. Sunday night/Monday...Operational/ensemble model spread is large regarding forecast conditions for this timeframe. One area of uncertainty is with placement of mid level ridging/trof for this timeframe. ECMWF has a blocking surface high to our N/NE, which could allow for wintry precipitation in our area. Other solutions are warmer/rain. Going with a model compromise for chance pops for this timeframe. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... 00Z Update... Tonight...High confidence for VFR conditions. Tuesday and Tuesday night...Moderate to high confidence. MVFR-IFR conditions overspread the region from west to east Tue morning in rain, low clouds and fog patches. Brief period of freezing rain possible at the onset across northwest and north central MA. Rain may be heavy at times Tuesday afternoon/early evening, particularly south of the MA pike where there may even be a rumble or two of thunder. Most of the rain ends by late Tue evening, and temporary improvement in CIGS may occur. However, any clearing will lead to areas of fog in the typically prone locations which may be locally dense for a time. Southeast wind gusts of 20 to 30 knots expected Tue afternoon/early evening along the coastal plain. LLWS may also affect some terminals. KBOS TAF...Moderate to high confidence in TAF. KBDL TAF...Moderate to high confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday...Moderate confidence. Patchy IFR/fog to start, otherwise initially VFR. Then deteriorating to IFR cigs/vsbys Wed afternoon and especially Wed evening as another round of moderate to heavy rain moves in. Rain exits overnight with conditions possibly improving to VFR late Wed night. Thursday thru Saturday...Moderate confidence. Mainly VFR cigs with isold MVFR possible. Blustery W winds expected. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Tonight...High confidence. A ridge of high pressure will keep winds and seas well below small craft advisory thresholds. Tuesday and Tuesday night...Moderate confidence. Impressive 50 to 60 knot low level jet develops by Tue afternoon and continues into the early evening ahead of a wave of low pressure. The result will be southerly wind gusts into the lower 30 knots. Small craft headlines posted all waters except Boston Harbor. There is the risk for a brief period of Gale force wind gusts, but given inversion over the waters opted to go with strongly worded small craft headlines. In addition, periods of heavy rain Tue afternoon/early evening along with fog will reduce VSBYS and there may even be a rumble or two of thunder. Outlook /Wednesday through Saturday/... Wednesday...Moderate confidence. Seas remain at SCA threshold across southern outer coastal waters, with building seas expected across the waters Wed night. Winds becoming E/SE and gusty during Wed afternoon/evening, and along the south coast winds become S during Wed evening. Vsbys lowering again in developing rain and fog later in the afternoon and Wed night. Thursday thru Saturday...Mainly W/NW winds with gusts to 25 kt at times. SCA seas persist over the south coastal waters. Good vsbys. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Freezing Rain Advisory from 4 AM to 10 AM EST Tuesday for MAZ002>004-008-010-026. RI...None. MARINE...Small Craft Advisory from noon Tuesday to 1 AM EST Wednesday for ANZ231-232-251. Small Craft Advisory from 10 AM Tuesday to 7 AM EST Wednesday for ANZ233>235-237-254>256. Small Craft Advisory from noon to 11 PM EST Tuesday for ANZ236. Small Craft Advisory from noon Tuesday to 7 AM EST Wednesday for ANZ250. && $$ SYNOPSIS...Frank/NMB NEAR TERM...Frank/Nocera SHORT TERM...Frank LONG TERM...NMB AVIATION...Frank/NMB MARINE...Frank/NMB

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