751 FXUS61 KBOX 121501 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA Issued by National Weather Service New York NY 1001 AM EST Thu Dec 12 2019 .SYNOPSIS... High pressure will bring dry, cold conditions across the region today and tonight. The high moves east of the region Friday, bringing the risk for scattered light precipitation across western Massachusetts and northern Connecticut, which may begin as a very light wintry mix. Temperatures will gradually increase Friday night as winds become onshore. Low pressure will bring mainly rain Friday night and Saturday which will fall heavily at times. Dry and blustery conditions move in on Sunday, then colder air arrives Monday. Another system brings snow to start Monday night, then a wintry mix that will change to rain across the coastal plain, but remaining mixed rain and/or snow well inland into Tuesday. Dry and cold conditions return during Wednesday. && .NEAR TERM /THROUGH TONIGHT/... 900 AM Update... Clear skies dominate across the northeast. Temps are warming through the 20s through 9 am. Near term forecast pretty much on track at 14Z. Previous Discussion... Large high pressure building into the region today will result in sunny skies but cold temperatures. Temps should top out between 30 and 35 across most locations with some upper 20s in the high terrain. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... * Risk for very light icing across parts of the interior Friday with the greatest threat across the CT River Valley Tonight... High pressure overhead this evening will allow for light winds and mainly clear skies this evening. This should result in temperatures quickly falling after sunset across the typically coldest outlying locations. Temps quickly drop into the teens this evening in many areas with light winds and snow cover. However, temps should level off or rise after midnight as clouds begin to increase from the west. This in response to high pressure moving off the coast and warm air advection commencing aloft. Friday... High pressure will continue to move east and away from the region as shortwave energy approaches from the southwest. This will induce a modest southwest LLJ and moisture return. The best forcing/moisture will reside across interior MA and CT, where some scattered light precipitation may develop. Ptype might be initially cold enough for a bit of very light snow across parts of the interior. However, warming aloft and limited saturation for ice nucleation may result in pockets of light freezing rain/freezing drizzle across the interior if temps remain below freezing for a time. The greatest risk for this will be across the CT River Valley, where high resolution model data indicates very light northerly surface winds persisting. Based on pattern recognition, guidance temps are likely too warm and it may take some time for temps to get above freezing even by Friday afternoon. If any icing occurs amounts will be very light, but it only takes a very small amount to create for hazardous travel. Something will have to examine more closely with latter model runs. Meanwhile, south to southeast low level flow should allow the coastal plain to reach into the 40s. Mainly dry weather should also persist across eastern MA/RI for much of the day, although can not rule out a spot shower or two late. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Highlights... * Temperatures will moderate Friday night as low pressure brings the potential for heavy rain & localized flooding on Saturday. Flooding risks may be increased with the snow melt. * Leftover rain and/or snow showers linger well inland early Sunday. Strong northwest winds Sunday, especially in coastal areas with gusts up to 40 kts. Gale headlines will likely be needed across the waters. * Dry and seasonably cold conditions Monday * Next system approaches Monday night & Tuesday...Another round of snow before mixing with or changing to rain, but confidence remains low. Details... Friday night and Saturday... ***Heavy Rain and Flood Potential on Saturday*** Low pressure exits the Maritimes Fri evening as low pressure develops across the mid Atlc states or near the Delmarva peninsula. Expect an increasing E-SE wind flow, which will bring deep moisture across the region. Temperatures will start off in the 30s well inland to 40-45 along the coast Fri evening, then the onshore winds will bring rising readings through the remainder of the night. 00Z models continue to signal a strong surge of deep layer moisture working up the coast. 00Z GEFS ensembles showing the potential of PWATs up to 3 to 4 SD above normal during Saturday across the coastal plain (1 to 1.5 inches). Overall model blend suggests QPF values from 0.5 inches across the CT valley ranging to 0.75 to 1 inch further E, highest along the immediate coast from 12Z-18Z Saturday, with another 0.1 to 0.3 inches Saturday afternoon. So, with this influx of heavy rainfall along with snowmelt thanks to the milder temperatures, the potential remains high for urban and poor drainage flooding especially across central and eastern areas. Will also monitor the potential for river level rises as well. Expect SE winds to increase during the day especially across eastern areas and along the coast, with gusts up to 20 to 30 mph Saturday morning through around midday before briefly diminishing. With the mild wind flow in place, expect temps on Saturday to top off in the mid-upper 40s well inland ranging to the mid 50s across the coastal plain. Saturday night and Sunday... ***Strong winds Sunday*** Low pressure exits to northern New England Saturday night, then to the Maritimes and Newfoundland during Sunday. Rain will exit from south to north Sat night, though could see a mix with snow across the E slopes of the Berkshires after midnight. With the diminishing moisture, QPF amounts will decrease so there will be only light snow accumulations there. Skies will become partly to mostly sunny across the coastal plain during the afternoon, while clouds linger further inland. With the low deepening across the Maritimes, down to around 980 hPa late Saturday night and Sunday, westerly winds will increase. Gusts will increase to 30 to 40 mph mainly across the higher inland terrain and along the coast. Temps will top off in the upper 30s to lower 40s across the higher terrain ranging to the upper 40s across the coastal plain. With the gusty winds, though, wind chills will be in the mid-upper 20s inland to the 30s elsewhere. Expect strongest wind gusts across the coastal waters, so gale warnings remain likely. Monday through Wednesday... Progressive mid level steering pattern remains in place across the region, so will see changing weather conditions continue. A mainly dry cold front moves offshore late Sunday night, so will see another surge of cold air working across the region to start off the work week. Highs on Monday will only reach the upper 20s to mid 30s well inland and across the higher terrain to the upper 30s to around 40 along the coast. Another weather system will approaches Monday night, with another shot of snow to start, then milder air will start to work in during Tuesday which should cause the snow to mix with sleet and snow, then eventually rain. However, this far out, timing and track of the low and precipitation potential is still in question. For now, looks like the precipitation should taper off late Tuesday night into Wednesday with continued cold temperatures. && .AVIATION /15Z 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 Night/... Today...High confidence in VFR conditions. Lingering NW wind gusts up to 20 kt across some E coastal Mass terminals until 18Z then will diminish. Tonight...High confidence. Mainly VFR conditions, but some MVFR cigs may arrive across parts of the interior toward daybreak. Friday...Moderate to high confidence. MVFR to IFR conditions dominate across interior MA & CT with scattered light precipitation expected to develop. It may be cold enough for some very light snow and/or freezing drizzle. Greatest risk for freezing drizzle would be across the BAF and BDL terminals. Meanwhile, across eastern MA and RI marginal MVFR to VFR conditions expected with mainly dry weather. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday through Monday/... Friday Night: Mainly IFR, with local MVFR possible. Breezy. RA likely, FZRA likely, patchy BR. Saturday: Mainly IFR, with areas MVFR possible. Windy with local gusts up to 30 kt. RA, patchy BR. Saturday Night: Mainly MVFR, with local IFR possible. Windy with local gusts up to 30 kt. RA likely. Sunday: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt. Sunday Night: VFR. Windy with gusts up to 35 kt. Monday: VFR. Windy with local gusts up to 30 kt. && .MARINE... Short Term /through Friday Night/... Today...High confidence. NW wind will diminish as high pressure builds in from the west. Wind gusts to 25 kt may linger through most of the day across the eastern waters. Tonight and Friday...High confidence. High pressure will be in control of our waters tonight keeping winds/seas below small craft thresholds. High pressure moves east of the waters Fri, allowing southerly winds to increase with gusts of 20 to 25 knots developing during the afternoon. We also may see some marginal 5 foot seas develop across our outer waters, so SCA headlines will need to be considered. Outlook /Saturday through Monday/... Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain likely. Local visibility 1 to 3 nm. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Rain. Local visibility 1 to 3 nm. Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 12 ft. Rain likely. Sunday through Sunday Night: Moderate risk for gale force winds with gusts up to 35 kt. Rough seas up to 13 ft. Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 4 PM EST this afternoon for ANZ250- 251-254. Small Craft Advisory until noon EST today for ANZ255-256. && $$