Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 081145 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 645 AM EST Fri Dec 8 2017 .SYNOPSIS... Dry and seasonably chilly weather will continue today. A winter weather advisory is in effect as a low pressure will bring the potential for moderate snow accumulations Saturday and Saturday night for much of southern New England. Still anticipate a mix of rain and snow confined to the Cape and Islands. Another coastal storm may bring more rain and/or accumulating snow Tuesday into early Wednesday. This storm will be followed by unseasonably cold and windy weather late Wednesday into Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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700 AM Update... Overall trend in the forecast remains on track for this morning. Difluent air continues to move across the region ahead of next approaching vort max. High level clouds will begin to overspread the region as vort max sharpens and digs farther south resulting in weak ridging and more southerly flow aloft. Today... Chilly start to the day as upper level shortwave begins to dive into the northern Great Lakes. This will result in a deepening trough in the Southeast with weak ridging over southern New England. Zonal flow in the mid-levels will turn more meridional which will help pull in moisture from the south. This will yield to an increase in cloud cover through the day. High temps will be similar to yesterday or just a few degrees cooler as cloud cover will limit heating during the afternoon. Overall expect mainly dry weather for today. However towards the evening, precip chances will begin to increase as approaching system from the Carolinas will start to push some moisture towards the Cape and the Islands.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... Tonight into Saturday night... *** Confidence is increasing in widespread 3-6 inches of snow for much of southern New England on Saturday *** Overview: Anomalous ridging over the West Coast with a broad upper level trough over the eastern two-thirds of the country. Several vort maxes moving through the trough will be the focus for our weather system tonight into Saturday night. The first is the southern stream wave which has produced snow down in south Texas. This wave will move over the Southeast and help develop a low off the coast of the Carolinas. The other piece of energy is still up in northern Canada and will quickly dive southward into the northern Great Lakes. By Saturday, these two systems will phase and deepen the offshore low pass the 40N/70W benchmark before moving towards the Maritimes by Sunday morning. Details: First significant snowfall for the region will occur late tonight and into early Sunday morning. Latest guidance members appear to come more inline than 24 hours ago on thermals and precipitation amounts leading to an increasing confidence on snow potential. Still some timing issues with the Hi-res guidance a bit on the slow side and the EC on the faster side of the envelope. NAM is a bit more robust on the QPF compared to the GFS/EC. Aside from some of these differences continued to trend the forecast towards a blend with more emphasis on the EC and GEFS/EPS. One thing to continue to watch is the axis of heavier QPF. Models are similar to previous run and keeps about an inch of QPF over Nantucket with 0.4 inches across Western MA and over 0.5 inches near the I-95 corridor. Feel that this is a good blend with all the guidance. However, with the northern stream wave getting closer to the region, feel that it will be sampled a bit better and thus cannot rule out a slight eastward or westward jog. Even if there is some wiggle, overall feel that this is a solid advisory event. Snowfall will begin to overspread the region late tonight and quickly take hold of the region Saturday morning. Expect p-type to stay all snow at the onset as temperatures will start out well below freezing. As the coastal low approaches the Benchmark during the day, thermals will become a bit more complicated as a warm layer begins to sneak into 925mb and surface temps warm along the coastline thanks to a developing coastal front. As the low pulls away cold air will wrap behind the system turning any liquid back to frozen by Saturday night. Forecast snowfall amounts is a general 3-6 inches with the potential for higher amounts across the Central Hills of Massachusetts and Rhode Islands. This region may have just enough QPF and higher snow ratios to push them above the 6 inch amounts. Confidence wasn`t high enough to issue a watch, but cannot rule out that this region could be upgraded to a warning. Locations across the Cape, Islands and will result in some mixing as surface temps warm and ocean waters are still in the upper 40s. More of a northerly flow in the later half of the day on Saturday will help keep some locations along the MA east coast as snow. did try to show the tight gradient in the snow grids. Continue to use a wet-bulb trend in the forecast by using high-res guidance to show lower temps within heavier rates. Intensity of the snowfall still a bit in question as stronger omega in snow growth region remains offshore, still some mid-level forcing which could help some places overperform. Overall this is a solid advisory event with a few spots having the potential to overperform. There is still the potential for this system to move farther west or trend more eastward. So please stay tune to the latest forecast. Just a reminder, this is the first snowfall of the season so motorist should use caution if traveling on Saturday. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Highlights... * Chilly temps Sun/Mon but with diminishing wind by Mon * Coastal storm may bring rain/snow Tue into early Wed * Unseasonably cold and blustery weather follows Wed into Thu Details... Sunday... While the steady snow will probably have come to an end by early Sunday morning, impressive shortwave will cross the region. This may bring a few snow showers to the region especially Sunday morning with lingering low level moisture. Otherwise, gusty northwest winds should develop as low pressure intensifies as it lifts into the Canadian Maritimes. High temps will mainly be in the 35 to 40 degree range, but it will feel colder given the gusty winds. Sunday night and Monday... Mainly dry and chilly weather expected as a weak ridge of high pressure temporarily builds into the region. Lows Sun night will be in the upper teens to middle 20s. High temps on Monday should be in the 35 to 40 degree range, but with much less wind than Sunday. Tuesday into early Wednesday... A lot of uncertainty in this portion of the forecast. Several pieces of vigorous shortwave energy will be dropping south into the Great Lakes. Depending on the specific timing/strength and just how far south the shortwave energy digs will have huge implications on our weather. A less amplified solutions would result in low pressure passing to our north with just some scattered rain/snow showers. A more amplified solution may allow for a rapidly intensifying coastal storm along with the potential for rain and/or accumulating snow. Later Wednesday into Thursday... Regardless of what happens with this system, unseasonably cold weather will be ushered in behind the storm later Wednesday into Thursday. It also may be quite windy for a time making it feel even colder. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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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 Saturday Night/... Today and tonight...High confidence. VFR through much of the day with clouds increasing from southeast to northwest. Lowest CIGS Nantucket/Cape Cod overnight, with the potential for IFR conditions across the Islands. Some light showers across ACK this evening, but precip shield will advance northwestward towards daybreak. Westerly winds will trend light and variable during the overnight hours. Saturday into Saturday night...High confidence in trends, but lower confidence in timing. Conditions will quickly drop to IFR through the day as snow spreads across all terminals. Potential for LIFR conditions Sat night across the I-95 corridor back towards ORH-IJD within any heavy snow bands. Snow accumulation across runways is increasing. Otherwise mixing of rain/snow most likely across the Cape and Islands leading to less snow/impacts. KBOS Terminal...High confidence in TAF. Lower confidence in precip timing. KBDL Terminal...High confidence in TAF. Outlook /Sunday through Tuesday/... Sunday: Mainly VFR, with areas MVFR possible. Windy with local gusts to 30 kt. Chance SHSN. Sunday Night: VFR. Breezy. Monday: Mainly VFR, with local MVFR possible. Breezy. Monday Night: Mainly MVFR, with areas IFR possible. Chance SN, chance SHSN. Tuesday: MVFR/IFR conditions possible. Breezy. Chance SN, chance RA.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Overnight into tomorrow... W winds will increase slightly this evening, with gusts to around25 kt. Seas respond, increasing to 5-6 ft on the ocean waters by early AM. Therefore, will continue small craft advisories through about mid-morning to mid day tomorrow, until seas gradually dissipate. Tomorrow night... Light flow shifts SW. Mainly quiet boating weather except for some SHRA on the SE waters. Outlook /Sunday through Tuesday/... Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 12 ft. Chance of rain showers. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 11 ft. Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain. Local visibility 1 to 3 nm. Tuesday: Winds less than 25 kt. Local rough seas. Chance of rain. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory from 4 AM Saturday to 7 AM EST Sunday for CTZ002>004. MA...Winter Weather Advisory from 4 AM Saturday to 7 AM EST Sunday for MAZ002>021-026. RI...Winter Weather Advisory from 4 AM Saturday to 7 AM EST Sunday for RIZ001>007. MARINE...Small Craft Advisory until 7 AM EST this morning for ANZ231>235-237. Small Craft Advisory until 10 AM EST this morning for ANZ250- 251. Small Craft Advisory until 1 PM EST this afternoon for ANZ254>256. && $$ SYNOPSIS...Frank/Dunten NEAR TERM...Dunten SHORT TERM...Dunten LONG TERM...Frank AVIATION...Frank/Dunten MARINE...Frank/Dunten is the U.S. government's official web portal to all federal, state and local government web resources and services.