Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 171807 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 207 PM EDT Sat Mar 17 2018 .SYNOPSIS... Mainly dry but unseasonably cold weather will continue into early next week. A multi-part storm system moves to the Mid Atlantic states midweek. This system may affect parts of Southern New England during midweek, but it is also possible the storm stays to our south. Currently there is low confidence on the eventual behavior of this storm. High pressure builds with drier weather Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 2 PM Update... Not much change from previous forecast. Band of clouds across northern MA including the north shore are associated with short wave trough and attending surface cold front moving southward from Maine. Lack of surface based moisture (dew pts in the teens) resulting high cloud bases around 6 kft. This combined with large dew pts depressions of 25 degs will likely preclude much if any snow shower activity reaching the surface. Thus other than some clouds from time to time and focused across northern and eastern MA, expect sunshine to continue. Blustery ahead and behind the front with gusts up to 40 kt this hour at Worcester, adding to the chilly conditions. Earlier discussion below. ================================================================== Another colder than normal day ahead for the region despite neutral temp advection. Potent mid level low and attending short wave over southeast Quebec into Maine rotates southeast this afternoon into eastern MA. Surface winds are backing to the southwest ahead of this feature and will result in another blustery day. At 10 AM temps are in the upper 20s and lower 30s but feeling much colder given the blustery WSW winds, up to 37 kt at Worcester! Mostly sunny conditions at late morning will trend toward partly to mostly cloudy this afternoon as some lake effect moisture streams eastward under cyclonic flow aloft. Additional moisture over northern New England associated with mid level low and attending short wave will move across eastern MA. Given depth of moisture is very shallow not expecting much more than an isolated snow shower/flurry this afternoon, with highest chance over east slopes of the Berks and across eastern MA. Otherwise mainly dry and cold conditions prevail today with another day of colder than normal temps. Normal highs for 3/17 should be about 45-48 degs, low 40s high terrain. Previous forecast captures these details nicely so no major changes with this update. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Overnight... With rising heights aloft, subsidence will lead to clearing and finally slacken the sfc pres gradient. This suggests clearing skies and a weak enough pres gradient for some radiational cooling. This will allow min temps to drop into the teens and even single digits at the obs sites normally prone to decoupling. Otherwise a dry night, one of the colder nights in recent past. Sun... A stretched vort-max pivots through the SW flow aloft, on the W periphery of a longwave trof across the Maritimes. Once again, the majority of the column is moisture starved, but with weak lift and NW flow some CAA SC is likely throughout the day, along with a risk for ocean enhancement along the Cape. Mainly dry otherwise. NW winds, but generally weaker than previous days as the core of the sfc pres gradient change is to the E. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Big Picture... Closed low over the Maritimes slowly ejects northeast. This keeps a cyclonic flow over New England early in the week. Southern jet stream remains in place most of the period with one shortwave moving east to the Mid Atlantic coast Tuesday and a second digging in over the Midwest Wednesday. This sets up a complicated flow to our south that generates multiple weather systems. These could easily pass to our south, or one of them may turn north and bring pcpn to Southern New England. Run-to-run trends on the operational models maintain dry weather Monday, so high confidence in that part of the forecast. Trends also push midweek precipitation farther south and mostly offshore. Ensemble runs still show possible scenarios that bring precip into our area midweek. Confidence in this part of the forecast remains low. Details... Sunday night and Monday... High pressure centered over Northern Ontario noses southeast over New England, and should provide sufficient subsidence for mostly clear skies. Mixing depth is forecast at 900 mb, with temps at that level supporting max temps in the 30s. Clear skies, light wind, and dew points in the teens should support Monday night min temps in the mid teens to lower 20s. Tuesday through Thursday... As noted, a complicated pattern is being projected by the models. There is a consistent trend of pushing the storm track farther south, with all operational models showing QPF mainly south of our region. The GFS does show 6 hours of precip south of a Plymouth- Providence line Tuesday afternoon. Also the ensemble members show greater potential for precip reaching farther north, contrary to the operational models. If there is any confidence in the model data, it is in showing multiple storm segments passing us during this period. Temperature profiles mostly support snow, expect for a rain-snow mix Wednesday. We have lowered pops a little, but maintain at least slight chance pops in general and chance pops across southern RI and parts of southeast Mass. This remains a low-confidence forecast, with all scenarios...a complete miss, a South Coast special, or a broader Southern New England event...continuing in play. Friday... High pressure builds over the region with dry weather and seasonably cool temperatures. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...High confidence. 18z update... VFR and dry weather thru Mon night. Gusty WSW winds up to 40 kt late Sat will shift to the NW up to 40 kt Sat evening behind a cold front, then diminishing later Sat evening. Not as windy remainder of the period including Sun thru Mon night. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Wednesday/... Tuesday: VFR. Breezy. Tuesday Night: VFR, with with areas of IFR possible on the South Coast. Windy with gusts to 35 kt. Slight chance SN. Wednesday: VFR, with areas IFR possible on the South Coast. Strong winds with local gusts to 40 kt. Slight chance SN. && .MARINE... Short Term /through Sunday/...High confidence. Today... W-NW Gales continue through the day. mainly on the eastern and ocean waters to the S of New England. These dissipate late this afternoon and evening, with lingering Small Craft Conditions to follow. Seas peak this morning 8-10 ft, and then begin to diminish. Tonight into Sun... Winds seas diminish overnight such that a brief period with conditions below Small Craft Advisory thresholds for a brief period late into early Sun AM. The winds turn NW and pick up 25-30 kt during the day on Sun, suggesting a need for Small Craft Advisories to continue. Outlook /Sunday Night through Wednesday/... Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Monday through Monday Night: Winds less than 25 kt. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Slight chance of snow. Areas of visibility 1 to 3 nm. Tuesday Night: Moderate risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Chance of snow, chance of rain, chance of sleet. Visibility 1 to 3 nm. Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 11 ft. Chance of rain, chance of snow. Areas of visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning until 7 PM EDT this evening for ANZ232>237. Gale Warning until 6 PM EDT this evening for ANZ230. Gale Warning until 8 PM EDT this evening for ANZ231-250-251- 254>256. && $$ SYNOPSIS...WTB/Doody NEAR TERM...WTB/Nocera/Doody SHORT TERM...Doody LONG TERM...WTB AVIATION...WTB/Nocera/Doody MARINE...WTB/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.