Area Forecast Discussion
Issued by NWS Boston, MA

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776 FXUS61 KBOX 172100 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 400 PM EST Tue Jan 17 2017 .SYNOPSIS... A mixed bag of wintry weather will impact much of S New England from late this afternoon into Wednesday morning. Could see leftover spotty showers lingering Wednesday. High pressure builds over the region for Thursday through the weekend with mainly dry and seasonably mild conditions. Low pressure developing off the Carolinas Saturday should remain well south of the region. A more significant storm may affect New England Mon into Tuesday with rain and/or mixed precip/ice along with strong coastal winds. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 300 PM Update... First short wave trough moving across the eastern Great Lakes early this afternoon with parent surface low of 1008 mb over Lake Erie. Warm advection precip associated with this feature was across much of NY state into northern NJ/NYC and Long Island. Latest meso analysis has pressure falls up to 4 mb in the past 3 hrs over the DC area. This will support secondary low pressure developing off DE/NJ coast later this evening and overnight. This combined with 1030+ mb high pressure over eastern Quebec will help advect dry/cold air into southern New England. Precipitation... Leading edge of precip continues to erode as it encounters very dry air across the region. This is apparent on the 18z observed sounding from ALY which reveals a very dry layer below 850 mb with a -20C dew pt at 925 mb! This yields subzero wet bulb temps thru the column except around zero just above 850 mb. This is a snow/sleet sounding with lots of evaporative cooling potential given magnitude of low level dry air. Timing... Onset of precip looks to be 3pm-5pm across CT and western-central MA...then moving east into RI and eastern MA 6-8 pm but possibly not until 9 pm for Cape Cod and the Islands given stubborn dry air below 850 mb. Impacts... Models in good agreement on burst of moderate to heavy precipitation around 22Z-02Z. Good snow growth signature at this time with strong lift in the DGZ. Where precip remains all snow could see snowfall rates of up to an inch per hour. However mid level warming as seen on the observed 18z ALY sounding just about 850 mb supports a mix of sleet and rain south of the MA Pike into northern CT and eventually freezing rain once surface wet bulb temps are realized. Eastward into RI and southeast MA probably a period of sleet given mid level warming. Farther northward into eastern MA including Boston a mix of rain/snow and sleet is likely with mainly snow north of the MA Pike and west of I495. This is where the worst travel conditions will be experienced. The heaviest precip will be this evening with somewhat lighter intensity overnight. Headlines... Not much change from previous forecast guidance as well as latest trends from radar and satellite imagery. Thus previous headlines and configuration of advisory still looks valid. Thus will continue will current headlines. Snow Potential... Looks like a swath of 2-4" north of the MA Pike and west of I495 with possibly up to 5 or 6" across the higher terrain in this region...northern Worcester county and northwest Franklin. Farther south an inch or two is possible to the MA/CT border and eastward into the I495 corridor. Elsewhere...less than an inch of snow and sleet across northern CT/RI into Metro-West Boston. Southeast MA and southern RI mainly rain with a bit of sleet this evening. Freezing Rain Potential... Mid level warming combined with shallow cold air will setup across the CT River Valley especially high terrain of Hartford county into southwest MA. A trace to a tenth of an inch of ice is possible with a tenth to a 0.25" possible across the high terrain of this region. This may result in isolated power outages. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... 3 pm Update... Nasty day for much of the region with a a cold wind swept rain during the morning for much of eastern MA and RI as secondary 1009 mb low well established near the 40N/70W benchmark. This combined with 1028 mb high over eastern Quebec will provide a gusty northeast winds into the region. Still could have snow falling across northern MA including interior northeast MA away from the coastline such as Lowell and Lawrence MA to the NH line. Best lift moves offshore after 12z so lighter precip the remainder of the day with any snow confined to the higher terrain. By the late day commute just looking at light spotty nuisance type precip. Chilly day with highs 35 to 40 but feeling colder along the coast given the gusty onshore winds. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Highlights... * Mainly dry with above normal temperatures Thu through the weekend * A storm may bring rain and/or mixed precip/ice Mon into Tue Overview... Models in agreement that persistent SE CONUS ridge will build northward along the east coast through the end of the week and into the weekend as active Pacific jet sends series of waves into the central CONUS. By the weekend southern stream system with Pacific origins will evolve into a closed low then lift toward the NE early next week. Given energy will not reach the west coast until this weekend, expect varying model solutions next several days. However, with lack of deep cold air snow will be difficult to come by with most of the precip likely in the form of rain or interior ice depending on positioning of downstream high pres and track of sfc low. Temps will remain above normal through the period. Details... Wednesday night into Thursday... Coastal low pres will move offshore in the evening. Abundant low level moisture persists Wed night so at the very least we expect lots of clouds during the night. Some light rain or interior snow may linger into the evening then sfc ridging should take control overnight Wed night into Thu. Morning clouds Thu should give way to partial sunshine in the afternoon as the column begins to dry. above normal temps with highs mostly in the 40s. Friday through Sunday... Surface high pres in control for much of the period as ridging aloft builds into the region. Result will be mainly dry weather but low level moisture will result in lots of clouds at times. Above normal temps trending cooler Sun as high pres sets up in the Maritimes with cold air damming signature. Coastal low emerging off the NC coast on Sat should remain far enough south to keep it dry. Monday into Tuesday... Inherent low confidence at this time range. Potential for a significant QPF event as southern stream system approaches but details unknown. EPS and GEFS probs for greater than one inch QPF are quite high at this time range with moderate probs greater than 2 inches. Potential for snow is low given lack of deep cold air but ice remains a threat in the interior given the presence of high pres downstream which could provide a source of low level cold air if sfc low can track south of New Eng. Variability in model solutions is likely until energy reaches the west coast this weekend. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 20z Update... Short Term /through Wednesday/...Moderate Confidence. Thru 00z... VFR to start but trending to MVFR as precip slowly overspreads the region from west to east. Burst of moderate to heavy precip toward 00z from west to east. May see snowfall rates of up to 1 inch per hour during this time...mainly western-central MA. After 00z... MVFR to start but lowering to IFR with LIFR likely across the high terrain. Moderate to heavy precipitation 00z-02z across RI and eastern MA mainly in the form of rain and sleet but snow westward into the Worcester Hills with snowfall rates up to an inch per hour. Freezing rain likely vicinity of BDL and BAF...possibly ORH too. ENE winds picking up by midnight and thereafter. Wednesday... MVFR with LIFR/IFR across the high terrain. Rain most terminals but rain and/or snow high terrain. Gusty NE winds eastern MA coast. Specific Terminals... KBOS TAF...bulk of precip will be rain however sleet and snow may mix in from 23z-01z. Gusty NE winds late tonight into Wed. KBDL TAF...Initial onset of RA transitioning to a wintry mix of SN/IP/FZRA. Light snow / ice accumulations are forecast with snow on the order of several tenths and several hundreds of an inch of icing. Outlook /Wednesday Night through Sunday/... Wednesday night into Thursday...Moderate confidence. MVFR/IFR cigs Wednesday night and early Thursday, improving to VFR from west to east during the day. NE gusts 25-30 kt Cape/Islands Wed evening diminishing overnight. Light winds Thu. Friday through Sunday...Moderate confidence. Areas of MVFR cigs possible at times, otherwise VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 3 pm Update... Short Term /through Wednesday/...Moderate Confidence. Tonight... ENE winds gradual increase tonight to 30 kt or so by morning...strongest wind vicinity of Cape Cod and Nantucket waters. Vsby lowering in rain with some sleet possible this evening. Wednesday... ENE winds up to 30 kt with strongest winds across the Cape Cod and Nantucket waters. Low risk for a few gusts up to gale force...35 kt. Vsby reduced at times in rain and fog. Outlook /Wednesday Night through Sunday/... Moderate confidence. Wednesday night...High confidence. Lingering NE gusts to 25-30 kt in the evening, diminishing overnight. Seas gradually subsiding. Thursday through Sunday...Moderate confidence. Light winds for much of the period as high pres builds over the waters. Lingering 5 ft seas over the outer waters Thu subsiding below SCA by Fri. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory until 7 AM EST Wednesday for CTZ002>004. MA...Winter Weather Advisory until 7 AM EST Wednesday for MAZ002>006-008>012-026. RI...None. MARINE...Gale Warning from 8 AM to 4 PM EST Wednesday for ANZ231-232- 254-255. Small Craft Advisory from 11 PM this evening to 7 PM EST Wednesday for ANZ230-233>237-250-251-256. && $$ SYNOPSIS...KJC/Nocera NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...KJC AVIATION...KJC/Nocera MARINE...KJC/Nocera is the U.S. government's official web portal to all federal, state and local government web resources and services.