Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 160327 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1027 PM EST Thu Feb 15 2018 .SYNOPSIS... Unseasonably mild temperatures continue tonight into midday Friday as another round of rain showers moves across the region. High pressure will bring dry but much colder conditions to the region Friday night into Saturday. A fast moving low pressure system will bring the potential for several inches of snow Saturday night into early Sunday morning. A significant warming trend is expected through mid week with the potential for near record high temperatures Tuesday and possibly Wednesday. Cooler weather returns Thursday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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10 pm update... Patchy dense fog continues to develop across portions of S New England where some faster diurnal cooling has occurred. Granted at this point there remains enough of a modest pres gradient to limit the extent. Still have issued an SPS to cover with this and will continue to monitor the possible need to upgrade to advisories. Otherwise, am a little concerned with latest radar signatures and short-fused guidance. The stronger convection across PA/NJ and S NY may actually usurp some of the moisture initially progged to move into New England overnight. In fact, runs from at least earlier this morning suggested PWATs across CT should be running around 1.00 inches, but are only just now seeing 0.8 inches per latest mesoanalysis data. Therefore, may actually see the bulk of the initially rainfall, associated with the remnant convection slide further S than previously progged, as it is along that S corridor that the highest PWATs, strongest moisture flux, and best instability parameters reside. Still S coastal areas will be scraped should see wetting precipitation during the early morning hours, but the risk for heavier rain may be lower than previously though. Further N, SHRA precip mostly associated with mid lvl convergence attendant to the actual shortwave could still deliver measurable precip. ECMWF is still slower with the the frontal passage, increasing this risk. Therefore will not adjust POPs too much after this initial round. Previous discussion... Noting another H5 short wave in the fast W flow aloft. With the low level SW wind flow, note northern edge of 1 to 1.2 inch PWAT plume push across RI/SE Mass overnight. This will bring decent QPF amounts, up to around 0.3 to 0.4 inches tonight across S RI/S Coastal Mass. May see some brief downpours along the S coast where best moisture convergence occurs. Also noting some marginal instability, but best remains S of the region so have not mentioned any thunder. Will see showers beginning across western areas between 03Z and 05Z, then will shift E through the remainder of the night. With SW flow in place, temps won`t fall too far. Expect overnight lows in the lower-mid 40s. However, will not see record high min temps for today, as the lows occurred early this morning. A cold front will start approach NW Mass after around 09Z.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday... Precip starts to taper off as short wave moves E and the cold front pushes offshore Friday morning. H85 temps start off at +4C to +6C, then will fall below 0C by midday across N Mass and continue to drop through the afternoon to -5C to -9C by evening. Heaviest precip already offshore by daybreak, so should only see about 0.1 inches or less in leftover showers through midday. Winds shift to W-NW by midday as colder air moves in. Also noting low level jet of 30-35 kt up to H9 with increasing low level lapse rates Friday afternoon. So, will see wind gusts up to around 25 kt or so across the higher inland terrain where highest lapse rates lie. Expect temps to top off in the lower-mid 40s across the higher inland terrain ranging to the lower 50s across the coastal plain by midday, then will drop off during the afternoon. Friday night... Strong cold air advection works in through the night on gusty NW winds. Still noting good low level lapse rates Friday evening so could see gusts up to 25-30 kt across the higher terrain, but better shot for 35 or even 40 kt across Cape Cod and the islands where another strong low level jet passes. Winds should diminish after midnight. Skies become mostly clear Friday evening through the overnight as large high pressure builds E out of the Great Lakes. Overnight lows will bottom out in the teens for most areas, except 20-25 along the immediate coast and lower CT valley. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * Potential for several inches of snow Sat night/early Sun morning * A period of showers Mon afternoon/evening * Warming trend through mid week with near record high temperatures possible Tue and Wed * Cooler weather returns Thu Saturday through Saturday night... High pressure will maintain dry weather through the day on Sat with temps a few degrees below normal. Sunshine will give way to increasing clouds in the afternoon. Confidence is increasing that fast moving southern stream wave will bring potential for several inches of snow Sat night, but there remains uncertainty where the axis of heaviest snowfall will set up and northward extent of ptype issues due to warming boundary layer. Robust mid level shortwave will induce cyclogenesis off the mid Atlc coast Sat evening with intensifying low pres tracking near or a bit south of the benchmark late Sat night. The amplitude of this shortwave will determine far north this wave tracks. The shortwave was over the Gulf of Alaska at 12z and better sampling of this feature will occur tonight and especially Fri when it moves into the western CONUS so additional shift in model solutions remain possible. This is a fast moving and progressive system so duration will be limited, with brunt of storm likely occurring in a 6 hour window, but moisture is plentiful and models indicating a period of strong omega through the DGZ for a time late Sat night. Thus a period of heavy snow is possible with 1"/hr snowfall rates, especially 03-09z. Thermal profiles suggest ptype will be mostly snow for much of the region, but warming boundary layer may introduce some ptype issues with a mix or changeover to rain, mainly over the islands and possibly the immediate south coast and Cape Cod for a time which would limit accum in this area. NAM is most robust with QPF but we discounted this for now given it is showing 80 kt low level jet which looks way overdone. GFS/GGEM is on the dry side of the model envelope with around 1/3" across RI and SE MA while ECWMF and UKMET have decent hit with 0.50-0.75" across SNE. We are still 2-3 days out in the model world so we blended the GFS and ECMWF with preliminary forecast of 3-6 inches across much of SNE, less over the islands and portions of Cape Cod. However, this is all track dependent and a more northward track would bring potential for more snow to the interior and less snow SE New Eng and coastal plain with snow to rain. A further south track brings less snow with most of it confined south of the Pike. Bulk of the snow should be over by daybreak. There is still a low risk for 6+" which would increase risk of isolated power outages if this fell over the coastal plain where snow will have a wetter consistency. Sunday... Any lingering light snow E MA will end quickly, otherwise clouds give way to increasing sunshine. Milder day with highs reaching the 40s so melting will occur. Monday through Thursday... An approaching warm front will bring a period of showers Mon afternoon/evening with temps well into the 40s and chance a few locations reach 50. Then a big warming trend is likely Tue and possibly Wed as anomalous ridge off the SE CONUS builds north along the east coast. SNE will be on the periphery of the ridge with cooler air lurking to the north so any subtle northern stream shortwaves which buckle the flow could bring cooler air southward, mainly Wed if this occurs. Temps in the interior should reach into the 60s Tue and possibly Wed as well. If front remains to the north Wed, temps could make a run at 70 degrees in the interior. ECMWF ensembles indicate 30-40 percent probability of 70+ in portions of the interior on Wed. Cold front moves through by Wed night with cooler post frontal airmass Thu with highs in the 40s. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... Tonight...Moderate confidence. Variable conditions this evening with VFR/MVFR and IFR near the coast, trending to MVFR/IFR overnight. Areas of LIFR in fog near the south coast. Showers move in toward midnight and continue overnight, steadiest near the south coast. Friday...Moderate confidence. Scattered -SHRA and patchy fog linger through mid to late morning with MVFR to local IFR conditions, then improving to VFR. W-NW winds gust to 25-30 kt across higher inland terrain and along immediate E coast Friday afternoon. Friday night...Moderate to high confidence. VFR conditions. W-NW winds gusting to 20-30 kt with local 35 kt across outer Cape Cod and Nantucket through 04Z-05Z, then diminishing. KBOS Terminal...Moderate confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Saturday through Tuesday/...Moderate Confidence. Saturday: VFR. Saturday Night: MVFR/IFR conditions possible. Breezy. SN. Sunday through Sunday Night: VFR. Washingtons Birthday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA. Monday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely. Tuesday: Mainly VFR, with local IFR possible. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. Through Tonight... SW winds increase to 10-15 kt through most of the night, then shift to W toward daybreak. Gusts up to 20 kt overnight across the eastern open waters. The persistent SW winds will keep ocean swells up to around 5-6 ft across the southern outer waters, so small crafts continue there. Visibility restrictions in patchy fog through early tonight, then in developing rain as well as areas of fog overnight. Friday... Winds become W-NW 10-15 kt, increasing up to 20 kt during the afternoon on the outer waters. Gusts will increase to 25-30 kt, highest on the eastern outer waters. Seas build up to 5-7 ft on the southern outer waters. Reduced visibility in showers and patchy fog through midday, then will improve as the showers and fog push offshore. Friday night... Expect NW wind gusts to increase to 35-40 kt on the eastern waters where Gale Warnings have been issued. Winds should diminish below gales after midnight. Small Craft Advisories has been issued or extended for the remainder of the waters. Seas build up to 7-10 ft. Good visibility. Outlook /Saturday through Tuesday/...Moderate to High Confidence. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Snow, rain. Local visibility 1 nm or less. Sunday through Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Washingtons Birthday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Monday Night: Winds less than 25 kt. Seas up to 5 ft. Rain showers likely. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 6 PM Friday to 6 AM EST Saturday for ANZ232. Small Craft Advisory from 5 PM Friday to 5 AM EST Saturday for ANZ230-233-234. Gale Warning from 6 PM Friday to 2 AM EST Saturday for ANZ231- 251. Small Craft Advisory from 6 PM Friday to midnight EST Friday night for ANZ236. Small Craft Advisory from 6 AM Friday to 6 AM EST Saturday for ANZ235-237. Gale Warning from 6 PM Friday to 3 AM EST Saturday for ANZ250- 254. Small Craft Advisory until 6 AM EST Saturday for ANZ255-256. && $$ SYNOPSIS...KJC/EVT NEAR TERM...Doody/EVT SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/EVT

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