Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 262244 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 644 PM EDT Wed Oct 26 2016 .SYNOPSIS... High pressure will push across the region tonight. Strong low pressure will push across the region late Thursday into Friday, which will bring a period of wintry weather well inland at the start, rain heavy at times elsewhere along with gusty winds at the coast. Another low passes to our north but swings a cold front through New England over the weekend. High pressure brings dry weather to the region Sunday through Tuesday. One more cold front moves through the region midweek. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 645 pm update... No significant changes to forecast. Satellite images show overrunning clouds spreading east across NY and PA. These should move into our area overnight. Adjusted a temperatures and sky cover a little. Previous discussion... Tonight...Another chilly night expected tonight as high pressure builds over southern New England. Away from the Cape and Islands, expect clear skies, calm winds, and excellent radiational cooling. On the Cape and Islands, ocean effect clouds and possibly a few ocean effect showers will keep temperatures there a bit warmer than the rest of the area. Most areas will freeze away from the immediate coast. Have issued a freeze warning for those areas that are still active in the frost/freeze program. In addition, because of the calm winds and increasing moisture, widespread frost is expected so have issued a frost advisory for the coastal zones that are still active, including Cape Cod. For Cape Cod, the main areas affected will be the upper Cape, away from the ocean effect clouds/showers. Block Island, Martha`s Vineyard, and Nantucket will likely be too warm for frost even so have kept them out of any headlines. Northwesterly winds will shift around to the north as the high builds in. This is a more favorable wind direction for ocean effect showers affecting the outer Cape and even farther west towards the mid Cape. Cold air aloft over the relatively warm ocean will provide enough instability for clouds certainly, as well as a few ocean effect snow showers. Given this would be the first instance of the season, do not anticipate any accumulation but residents may see some flakes during the overnight period. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Snow potential...High pressure over Quebec is pushed to the east as low pressure in the Great Lakes slowly moves eastward. This approaching low pressure system will shift winds to the east- southeast allowing for increasing moisture into the region. Coupled with that are the frigid temperatures both at the ground and aloft, making for an area conducive to some snow to start out. This low pressure system remains dominant through most of the day, giving way to a secondary low that forms somewhere over the tri-state region and moves up over southern New England Thursday night. The timing of this interaction and the transition of power to the secondary low will be a big player in determining duration and extent of snow. Expect snow to move into the SW zones shortly after sunrise and proceed to the NE quickly. Expect snow to remain north and west of I-95, and likely most of it will be north and west of I-495 as well. Little to no accumulation is expected, particularly at the lower elevations. Elevations above 1500 ft may see a light dusting. However, the timing of the onset of snow and the fact that it will be the first widespread snow of the season, expect some impacts to the morning commute as we all get our snow tires under us, so to speak. Rain potential...While east of the I-95 corridor will remain all rain, expect all areas to change over to rain around noon. Precipitable waters are rather high for this time of year, around 150% of normal, so this rain will be heavy at times. Heaviest precip is expected to be during the overnight period, particularly as the dry slot approaches, instability increases somewhat, and the low level jet increases as the warm sector moves over southeastern New England. Expect anywhere from about three-quarters of an inch of rain to just over an inch of widespread rainfall. A few areas may see more than this, some may see less. It depends on how convective the rain gets during the overnight hours. This shouldn`t cause any widespread flooding issues. Mostly just poor drainage and urban flooding. Wind potential...Low level jet increases Thursday night as it moves across Rhode Island and SE Massachusetts. This coupled with the rain and potential convection may result in strong, gusty winds mixing down to the surface. Wind advisory criteria may be hit on the Cape and Islands, as indicated by Bufkit model soundings. Think there is a decent chance of that occurring but am not quite confident enough to put up a winds advisory. Will give the mid shift another chance to look at it before hoisting a headline. Temperatures...While Thursday morning will start out rather cold, temperatures will rebound throughout the day. While temps will not be much warmer than they have been today, the real recovery will be during the overnight. Not expecting widespread freezing temperatures Thursday night, with temperatures warming in some areas overnight. As the warm sector moves over RI and SE MA, expect temperatures to increase through the 40s and possibly into the lower 50s early Friday morning. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Big Picture... High pressure over the Southern tier of the USA while closed Upper low hovers near Hudson`s Bay. This places New England in a zonal flow with several shortwaves moving through the flow. Models agree on bringing 3 or 4 shortwaves through our area during the upcoming week, but with differences in timing. Expect variable differences to continue with each model run for the next couple of days. Details... Friday... Upper shortwave and associated surface low are over Southern New England Friday morning, and move off to the east during the day. Expect lingering scattered showers in Northern MA and on Cape Cod, diminishing during afternoon. Lingering moisture below 850 mb should allow partly to mostly cloudy skies through the day with partial clearing at night. Mixing to 925 mb will allow wind gusts of 30 to 35 knots. Temperatures in the mixed layer will support max temps in the upper 40s and 50s. Saturday-Sunday... Shortwave from Central Canada sweeps across New England. Timing currently looks like late Saturday and Saturday night, although the ECMWF has passage on Sunday. Wind fields show some upper venting and low level convergence with this system. Moisture fields show PWs of 1.4 inches, but are limited in the vertical with some available moisture below 700 mb along and ahead of the front. Will forecast chance pops mainly north of RI and CT, slight chance farther south. Monday-Thursday... High pressure builds over the region Monday through Wednesday. This should be a period of dry weather. Coolest temps aloft are on Monday with a warming trend through Wednesday. One upper shortwave passes well to our north on Wednesday. Most of the support for this remains in Canada, but some indications in the models that a wind shift may be forced south to our area on Wednesday. Little or no pcpn is associated with this. Another shortwave dives south from Northern Canada to the Great Lakes Thursday, and may spread showers our way Thursday night. But timing on this feature is low confidence at best. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/... Tonight...High confidence. Mainly VFR. Low end VFR to MVFR ceilings expected over Cape Cod and Nantucket. Low probability of periods of MVFR conditions in ocean effect snow showers in this area. Northerly winds diminish except for on the Cape and Islands where gusty winds continue. Thursday...High confidence in trends, lower on timing. Conditions quickly diminish as a mix of snow and rain showers sweep into southern New England from SW to NE. Most likely period for snow will be during the morning hours and across northern CT and western and central MA. Elsewhere, rain is expected. Snowfall will be light and no accumulation is expected on pavement. In fact, any accumulation will likely be limited to the higher elevations (greater than 1500- 2000 ft). All areas of snow should change to rain quickly by 18Z. Northerly winds shift to the east during the day but remain fairly light until after 21Z, when the low level jet kicks up and areas along the south coast, Cape, and Islands will see gusts starting to increase up to 25 to 30 kts. Thursday night...High confidence in trends, lower on timing. Rain will continue through the night with a periods of heavy rain possible. Expect a mix of MVFR/IFR conditions in rain/fog. On the coastal plain, the south coasts of RI/MA, the Cape and Islands, easterly to southeasterly winds will gust up to 35 to 40 kts at times. Elsewhere, winds will be a bit lighter, gusting up to 20 to 25 kts along the east coast and below 20 kts across the interior. KBOS TAF...High confidence in trends, lower confidence in timing. KBDL TAF...High confidence in trends, lower confidence in timing. Outlook /Friday through Monday/... Friday... Moderate confidence. Areas of MVFR cigs/vsbys in showers early, but trending VFR during the day. Northwest winds increase with gust potential 30 to 40 knots. Saturday-Sunday... Low confidence. Mainly VFR but with brief MVFR in scattered or widely scattered showers. Timing is uncertain. WSW winds gusting 20 to 25 knots Saturday, becoming NW and diminishing Sunday. Monday-Tuesday... Moderate confidence. VFR. North winds less than 20 knots becoming light variable. && .MARINE... 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...Winds and seas trend lower as high pressure moves over the waters. Lingering ocean effect clouds and possibly snow showers near Cape Cod and Nantucket may limit visibilities at times. Thursday...Winds and waves will build slowly as low pressure approaches southern New England from the Great Lakes. Small craft conditions may be reached by the evening hours but will quickly be followed by easterly gale force wind gusts. Thursday night...Easterly and then southeasterly gale force wind gusts are expected Thursday night and into Friday. Gale Watches have been issued for this time for most of the waters. Waves increase to 7 to 9 feet on the outer waters. Periods of heavy rain and fog may limit visibilities at times. Outlook /Friday through Monday/... Moderate confidence Friday... Moderate confidence. Low pressure over Southern New England moves off past the Maritimes. Winds will increase from the Northwest with frequent gusts of 35 knots. Seas will hold at 5 to 10 feet on the exposed waters, diminishing Saturday night. The Gale Watch has been extended into Friday on most waters. Saturday-Sunday... Low confidence. Cold front moves across the waters during the weekend. Low confidence on timing of the passage. Expect WSW winds ahead of the front with gusts to 25 knots, then NW winds behind the front with speeds 15 knots or less. Seas 5 to 9 feet Saturday on the outer waters and the RI waters. Seas then diminish Sunday. Monday-Tuesday... Moderate confidence. High pressure builds fair weather over the waters. Winds less than 20 knots and seas less than 5 feet. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Frost Advisory from 10 PM this evening to 9 AM EDT Thursday for MAZ007-015-016-019-022. Freeze Warning from 10 PM this evening to 9 AM EDT Thursday for MAZ014-018-020. RI...Frost Advisory from 10 PM this evening to 9 AM EDT Thursday for RIZ005-007. Freeze Warning from 10 PM this evening to 9 AM EDT Thursday for RIZ001>004-006. MARINE...Gale Watch from Thursday evening through Friday afternoon for ANZ231>235-237-256. Gale Watch from late Thursday night through Friday morning for ANZ230. Gale Watch from late Thursday night through Friday afternoon for ANZ250-251. Gale Watch from Thursday evening through Friday afternoon for ANZ254-255. && $$ SYNOPSIS...WTB/RLG NEAR TERM...WTB/RLG SHORT TERM...RLG LONG TERM...WTB AVIATION...WTB/RLG MARINE...WTB/RLG is the U.S. government's official web portal to all federal, state and local government web resources and services.