Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270806 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 406 AM EDT Thu Oct 27 2016 .SYNOPSIS... Strong low pressure will push across the region late Thursday into early Friday, which will bring a period of snow well inland this afternoon. Elsewhere rain heavy at times this afternoon and tonight along with gusty winds at the coast. Drying trend Friday but becoming breezy behind departing low pressure. A cold front may bring a few showers to the region Sat afternoon and evening. Low pressure may form on this front and bring the risk for a period of rain to the area Sunday. Dry much of next week with temperatures cool Monday but becoming mild Tue and Wed. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 11 PM Update... Mid and high clouds have pushed NE across central and western areas through 03Z as seen on IR satellite imagery and OBS over the last few hours. Temps have already fallen to the mid and upper 20s across the Mass portion of the CT valley into central Mass, and the lower-mid 30s away from the immediate coast. Dewpts have risen to between 20 and 25 degrees across most areas, though a bit higher along the S coast. Light N-NW winds continue as the high pres ridge builds slowly E out of E NY state. While high clouds have pushed in, they are thin enough to allow temps to continue to fall with good radiational cooling. Patchy low clouds and spotty showers have moved across outer Cape Cod over the last couple of hours. Noting increasing area of showers across eastern Cape Cod Bay into the mid and outer Cape as well as into eastern Nantucket Sound as seen on latest KBOX 88D radar trends. Have adjusted cloud cover to increase coverage, as well as temps/dewpts to bring conditions current as well as incorporating into near term trends. Previous discussion... 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 light winds and increasing low level 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. Expect light N winds as the ridge 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 showers or flurries overnight. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... 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/... 4 am update... Highlights... * Temps more seasonable this period * Risk of a few showers late Sat, a more widespread rain Sunday? * Mainly dry and seasonable much of next week Friday... At 12z triple pt low somewhere along northeast MA coastline and continuing to deepen/strengthen as mid level low approaches from NY state. Dry slot thru the region so drying trend develops with just some leftover showers across northern-northeast MA early Fri morning. However system becomes vertically stacked by afternoon as mid level low captures surface reflection off the NH/ME coast. This may result in comma head showers rotating back into northeast MA and clipping the outer Cape Fri aftn. Elsewhere dry weather should prevail along with increasing northwest winds as low continues to deepen off NH/ME coast. Probably more clouds than sunshine given cyclonic flow aloft persisting across the region. High temps will likely be observed in the morning especially across RI and eastern MA where leftover warm sector will yield morning highs of 55-60. Low to mid 50s elsewhere with upper 40s higher terrain. Weekend... Uncertainty as models continue to struggle with amplitude of lead (Saturday) and trailing (Sunday) northern stream short wave energy. As of now models bring low pressure across northern New England Sat with attending cold front entering southern New England late Sat and Sat night. This may be accompanied by a few showers but much of the day and night will remain dry. Then on Sunday both GFS and EC suggest trailing northern stream short wave energy will be robust enough to spawn a weak frontal wave on the front before boundary exits southern New England. This would yield a risk of rain overspreading the region Sunday from west to east. 00z GEFS ensembles have shifted in this direction as well. Given time range and uncertainty will follow a model blend and trend the forecast toward Sunday having the higher probability of rain of the two weekend days. Temps will be more seasonable than recent days with highs both Sat and Sun 55-60. Although if frontal wave verifies Sunday could be the cooler day given precip potential Monday thru Wednesday... Brief cool down Sunday night and Mon behind departing northern stream short wave. However temps rebound nicely Tue and Wed as subtropical ridge over the southeast states builds northward up the Eastern Seaboard. Mainly dry this period with a low risk of showers sometime around Wed as northern stream energy and attending cold front move into New England and begin to erode the northern portion of this subtropical ridge. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Overnight...High confidence. Mainly VFR. Low end VFR to MVFR ceilings expected over outer Cape Cod and Nantucket. Low probability of periods of MVFR conditions in ocean effect rain or 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/... 4 am update... 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. VFR likely Sat with perhaps a period of marginal MVFR in scattered showers late Sat/Sat night. Possible MVFR-IFR Sunday across CT/RI and southeast in periods of rain. Monday-Tuesday...Moderate to high confidence. VFR and mainly dry weather. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence. Overnight...Winds and seas trend lower as high pressure moves over the waters. Lingering ocean effect clouds and possibly rain/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/... 4 am update... Friday... Moderate confidence. Gale center near Cape Ann early Fri moves slowly into Gulf of ME Fri afternoon. WNW gales all waters. Saturday-Sunday...Low confidence. Southwest winds 20-30 kt Sat ahead of approaching cold front. Wind shift Sunday morning to north behind departing front. However boundary is slow to depart as low pres may form on the front over NJ and then tracks south of Long Island Sun aftn and then across Georges Bank Sunday night. Monday-Tuesday...Moderate confidence. Modest north winds Mon behind departing low pressure. Light winds Tue as high pres crest over the area. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Frost Advisory until 9 AM EDT this morning for MAZ007-015-016- 019-022. Wind Advisory from 1 AM to 10 AM EDT Friday for MAZ007-014>024. Freeze Warning until 9 AM EDT this morning for MAZ014-018-020. RI...Wind Advisory from 11 PM this evening to 5 AM EDT Friday for RIZ007-008. Frost Advisory until 9 AM EDT this morning for RIZ005-007. Freeze Warning until 9 AM EDT this morning for RIZ001>004-006. MARINE...Gale Watch from this evening through Friday morning for ANZ231>234. Gale Watch from late tonight through Friday morning for ANZ230. Gale Watch from this evening through late tonight for ANZ236. Gale Watch from this evening through Friday morning for ANZ235- 237. Gale Watch from late tonight through Friday afternoon for ANZ250-251. Gale Watch from this evening through Friday afternoon for ANZ254-255. Gale Watch from this evening through Friday afternoon for ANZ256. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...Nocera AVIATION...Nocera/EVT MARINE...Nocera/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.