Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 152103 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 403 PM EST Mon Jan 15 2018 .SYNOPSIS...
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Chilly this evening with wintry mix including snow and freezing drizzle impacting eastern MA. Low pressure drives east from the Great Lakes Tuesday, then redevelops off the Mid Atlantic coast. This will bring the potential for several inches of snow to portions of the region mainly late Tuesday into Wednesday afternoon...but precipitation type is uncertain southeast of the Boston to Providence corridor. Mainly dry weather likely Thursday into Sunday, with a warming trend during the weekend. Another low pressure system may affect our region early next week.
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&& .NEAR TERM /THROUGH TUESDAY/...
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* Freezing drizzle and snow for the evening commute Complicated forecast as developed just in time for the evening commute. Persistent easterly flow coming off the ocean as helped saturate the low levels down to the surface. Aloft however, there is some dry air which has resulted in a lost of moisture within the snow growth region. This includes from -12 down to -8C which is favorable for ocean effect. Thus areas of freezing drizzle has developed early this afternoon and continues to move into the region. Several reports of motor vehicle accidents have occurred across the south coast up towards the south shore. Because of the slick travel, went ahead an expanded the winter weather advisory for southern Plymouth. Outside of there, southern Bristol and the Cape, went ahead with an SPS as this region seems to be more scattered then widespread. Also went ahead and transitioned the winter weather advisory for more of a mixed precip and glaze of ice event versus the higher snow amounts. The lack of moisture in the snow growth region today has undercut amounts just a bit. Mid-level moisture does increase later this evening which will help increase any snow potential versus freezing drizzle/ice. However, the biggest question is if the convergence zone will still be set- up. Latest hi-res and soundings suggest that it will be, but just a bit farther south thus missing Essex and Suffolk county. This is supported by current obs which are more north/northwest versus the preferred northeast. Therefor anticipate just a few flurries across the north shore and the city of Boston while the south shore and Plymouth county have a better shot of seeing an additional inch or two of snowfall this evening and into tonight. Tuesday... Ocean effect snow showers will slowly come to an end by Tuesday morning as winds become light and we loose the convergence region. Approaching system from the west will help flip wind to a more southerly direction by the afternoon hours. Guidance continues to suggest more or a southwest flow aloft as WAA moves in the region. This will help keep the region socked in with clouds, however temperatures do warm into the low to mid 30s. Within this warm advection pattern, snow showers will break out across the area with some moderate lift in the snow growth region. The Tuesday evening commute may be impacted especially across western MA but the bulk of this system will occur Tuesday night into Wednesday. See the short term section for more details.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... Tuesday night through Wednesday night... Upper trough over the eastern USA with jet core 130-145 knots. The trough axis maintains a progressive orientation through midweek. The right entrance region of the jet moves near the Carolina coast Tuesday evening, which will generate cyclogenesis along the coast. The resulting coastal low will then move up the coast overnight and pass Cape Cod and Islands Wednesday afternoon/evening. Cross sections show some initial elevated lift early Tuesday night, but the best and deepest lift over Southern New England runs from after midnight until midday Wednesday. This will be the best time for accumulating snow. There are differences among the models regarding the track of the storm center. The NAM and GFS are slower and pass about 70 miles inside 40N/70W, while the GGEM and ECMWF are about 6 hours faster and pass directly over Cape Cod. We favored the offshore track. QPF continues to be expected in the 0.40 to 0.75 inch range, with snow to liquid ratios of between 12 and 15 to 1 in the interior and 10 to 12 to 1 in much of RI and Southeast MA. This supports 6 inches or higher over much of the region, with diminishing amounts south of a Boston-Hartford line due to temperatures near freezing along with a mix or change to rain. This brings the heaviest snow over interior Southern New England, affecting an area broader than the current watch. We have expanded the existing Winter Storm Watch to include Northern CT, NW RI, and Norfolk/Suffolk Counties in MA. The upper trough sweeps overhead Wednesday night. Expect diminishing snow in advance of this Wednesday afternoon and night. Thursday... Model trends are sufficiently progressive to push any new development well offshore and away from New England. The outlier solution comes from the GGEM, which maintains a closed upper low over the VA-Carolina coast Wednesday night/Thursday morning with surface low pressure just outside the benchmark and an upper flow guiding its moisture toward Cape Cod. We are discounting the GGEM solution and maintaining a dry forecast for Thursday with partly to mostly sunny skies and northwest wind. Temps aloft equiv to 850 temps of -15 to -17, so surface max temps should be roughly 25 to 30. Thursday night dewpoints in the teens and west wind 5 to 10 knots suggest min temps 15 to 25. && .LONG TERM /FRIDAY THROUGH MONDAY/... Fri... At the surface the area is still under the influence of a broad area of high pressure. Models show a quick hitting mid level short wave crossing thru southern New England during the day however there is not much moisture associated with this feature. This far out there could certainly be uncertainty on exact timing and whether or not it brings light precip in addition to some clouds. Thinking at this time will go with a slight chance pop for light snow on Friday, but main effect should be some clouds. Sat and daytime Sun... High pressure centered offshore and well south of New England remains our primary weather feature. W/SW return flow brings in warmer air, hence expecting a moderation of the airmass over the course of the weekend. Going with high temps in the 40s Saturday, and mid 40s to low 50s on Sunday. In comparison, normal high temps are currently in the 30s. Overall dry weather is likely. Soundings show the influence of the high pressure in the form of a broad subsidence inversion. Sun night... Warm front approaches from the west as a low pressure system centered over the western Great Lakes Region deepens. At this point not anticipating much by way of precipitation in our area, but could see some light rain or a light wintry mix over a portion of our region. Will go with slight to low chance pops. Early next workweek... Models indicating potential for Great Lakes low to move eastward, bringing precipitation associated with a cold front thru southern New England. With southerly flow ahead of the front, anticipating that this would be a initially a rain event, though could end as a period of wintry mix or snow. Could also be windy ahead and along the front, as models are showing potential for a strong low level jet. However, this far out there is still a lot of uncertainty, from both a timing and p-type standpoint. So plan to go with chance pops at this time. && .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/... Tonight...Moderate to high confidence in TAF. Wintry mix across eastern MA should wind down after 6z. Mixture of MVFR/VFR cigs with lowest conditions across eastern MA including the Cape and the Islands. Tuesday...Moderate confidence in TAF. Any VFR will fall to MVFR cigs through the day. Light snow showers will over spread the region by the afternoon esp across western MA. Tuesday night-Wednesday... Mainly IFR/LIFR cigs/vsbys in snow, with areas of heavy snow north of a BOS-HFD line. Snow may mix with or change to rain south of a Marshfield-Providence-Westerly line. Conditions improve to VFR in CT and Western Mass Wednesday afternoon...and in RI and Eastern/Central Mass Wednesday night. Wind gusts 25 to 30 knots around Nantucket and parts of Cape Cod. Thursday...VFR. Northwest winds gust to 25 knots Cape Cod and Islands, with gusts to 20 knots elsewhere. KBOS Terminal...Moderate confidence in TAF. Should remain snow free, but cannot rule out a few flurries during the evening push. KBDL Terminal...High confidence in TAF. Outlook /Friday through Saturday/... VFR. Breezy.
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&& .MARINE...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/... High confidence. Tonight into Tuesday...Easterly winds overnight with gusts near 20 kts will diminish by the morning. SCA has been expanded as seas will remain about 5 feet or more into tomorrow. Tuesday night...Easterly winds with gusts to 25 knots overnight. Seas 5 feet on the outer waters. Mixed snow and rain developing. Visibility 4 to 6 nm. Small Craft Advisory may be needed. Wednesday...Easterly winds with gusts 20 to 30 knots. A few gusts to 35 knots possible southeast of Nantucket. Seas 5 to 7 feet on the outer waters and possibly on the RI waters. Rain and snow will diminish in the afternoon. Visibility 2 to 4 miles. Small Craft Advisory may be needed. Low chance of a gale warning southeast of Nantucket. Wednesday night...Winds turning from northwest at 20 to 25 knots. Seas remain at 5 to 7 feet on the outer waters. Snow tapers off at this time. Small Craft Advisory may be needed. Thursday...Northwest winds gusting to 25 knots. Seas remain 5 to 7 feet on the outer waters. Small Craft Advisory may be needed. Outlook /Friday through Saturday/... Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.
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&& .HYDROLOGY... Minor flooding continues along Taunton and Pawcatuck Rivers where Flood Warnings remain in effect. A Flood Warning is also in effect for the Connecticut River at Hartford and Middle Haddam, where ice is causing some river fluctuations. Colder weather will persist through midweek which will limit additional runoff, although we should see some building of snow pack for much of region Tuesday into Wednesday. For details on specific area rivers, including observed and forecast river stages, please visit the Advanced Hydrologic Prediction Service /AHPS/ graphs on our website. && .EQUIPMENT... The Taunton, MA WSR-88D (KBOX) has been returned to service. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Watch from Tuesday afternoon through Wednesday afternoon for CTZ002>004. MA...Winter Weather Advisory until 10 PM EST this evening for MAZ016-018-019-021. Winter Storm Watch from Tuesday afternoon through Wednesday afternoon for MAZ005>007-013>016-026. Winter Storm Watch from Tuesday afternoon through Wednesday afternoon for MAZ002>004-008>012. RI...Winter Storm Watch from Tuesday afternoon through Wednesday afternoon for RIZ001. MARINE...Small Craft Advisory until 1 AM EST Tuesday for ANZ231>235-237. Small Craft Advisory until 8 PM EST Tuesday for ANZ250-251- 254>256. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...Dunten SHORT TERM...WTB LONG TERM...NMB AVIATION...WTB/Dunten/NMB MARINE...WTB/Dunten/NMB HYDROLOGY...NMB EQUIPMENT...Staff

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