Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 300839 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 339 AM EST Wed Nov 30 2016 .SYNOPSIS...
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A brief period of dry weather this morning into early afternoon before another round of soaking rain affects the region late this afternoon and into tonight. Dry weather returns Thu and persist into much of the weekend along with a trend toward cooler temperatures. For early next week...latest trends suggest cool weather with a chance of wintry precipitation Sunday night into Monday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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330 am update... *** Dense fog CT River Valley/I-91 corridor this morning *** *** Rain...heavy at times returns late this afternoon & night *** Dense Fog... Winds have decoupled in the CT river valley and coupled with low level moisture /dew pts in the upper 40s to lower 50s/ has resulted in dense fog to form. Thus have issued a dense fog advisory for this region until 14z/9am...with slow improvement thereafter. Elsewhere areas of dense fog may form toward sunrise as winds diminish. This coupled with relatively high dew pts for this time of year may be sufficient for additional areas of dense fog to develop toward sunrise. The south coast may be another area to watch for locally dense fog given moist sw winds off the relatively warm ocean waters. Wildcard here will be mid and high clouds racing northeast toward the region from the southwest. This cloud cover may result in temps warming a bit and give way to increasing vsbys and cigs lifting. Will watch the evolution closely this morning. Fog will begin to burn off later this morning as BLYR mixes out along with some breaks of sunshine before skies become overcast by midday. Rainfall... Next southern stream system approaches late today. Model soundings show low level dry air taking sometime to erode so steady rains may hold off until 21z or so. Triple point low approaches from the southwest late along with PWATs climbing to +3 standard deviations above climo. This will result in periods of heavy rain 21z-00z with greatest threat over the interior...closer to track of triple point low. Temps... Mild start to the day especially across CT/RI and southeast MA where lingering warm sector is resulting in temps in the 50s at 3 am!
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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330 am update... *** Another soaking rain this evening & overnight *** Tonight... Rainfall... As mentioned above subtropical airmass overspreads the region with PWATs up to +3 standard deviations from climo. Heaviest rain will fall vicinity of triple point low where convergence is maximized. Widespread rainfall amounts of 0.50 to 1.0 inches will be common but up to 2+ where triple low tracks...most likely across the interior. In addition marginal elevated instability may yield an isolated rumble of thunder across the south coast of MA and RI. Heaviest rain 00z-06z and then ending 09z-12z from west to east. Only flooding will be minor street and highway. So some impact to the tail end of the late day commute. Wind Potential... Another strong low level SSW jet of 50 to 60 kt will cross the south coast 06z-12z tonight into Thu morning. However as was the case yesterday models soundings suggest low level inversion will preclude strong winds aloft from reaching the surface. Can`t rule out an isolated wind gusts greater than 45 mph...however the greater risk is for sustain winds to exceed 30 mph. Given uncertainty/low forecast confidence the day shift will have to evaluate model trends for a potential wind advisory based on sustained winds across the south coast tonight into Thu morning. Thursday... Big improvement as parent and triple pt lows move north and east of the region with deep layer subsidence overspreading the area. Thus sunshine returns and with CAA lagging until Thu night...highs of 55- 60 seem possible. Although morning sunshine will fade behind diurnal strato-cu per model RH profiles. In addition a gusty west wind of 20- 30 mph will provide a bit of chill. Overall still above normal for the first day of Dec.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ Highlights... - Near seasonable, dry pattern with breezy NW winds late week into the weekend - Initial wintry mix changing over to all rain possible early next week */ Overview... Perhaps an over-running onset of mixed wintry precipitation events, but otherwise a warm-wetter pattern continues. La Nina is seemingly the dominant influence upon the N Hemisphere as all other atmospheric teleconnections are near-neutral, relatively flat. A more buckled pattern than idealized across N America, with strong C CONUS cyclo- genesis drawing down colder air W beneath a favorable region of troughing while latching into tropical maritime air S. Would appear with prevailing E CONUS downstream ridging, deepening and occluding storm centers out of the C CONUS are stretched N/W of S New England, inside-runners, placing S New England in the warmer and wetter region of outcomes. A progressive pattern of initial over-running followed by a sweeping cold front before high pressure and colder air settles back in. Can not rule out a continuation of mixed wintry precipitation events with the onset of storm systems noting the potential for cold air damming and triple point lows. Will note in the details below. Would appear Arctic air presently is locked up round the polar low. Indications though that as we go towards mid-December the polar low and associated energy becomes displaced. Associated jet stream round the maritimes becomes buckled and more amplified. Potentially thus we could see shots of Arctic air being introduced as we go deeper into Winter. No doubt if the pattern continues we would see such air slide S across the Rockies into the C CONUS before sliding E, likely moderating. It`s early but worth noting of potential trends down the road, something to watch. */ Details... Thursday through the Weekend... NW flow and cold air advection initially through which mid-level energy and moisture continue to rotate round a dying low pressure center over the N/E Great Lakes Region. A reinforcing cold front inbetween around Saturday morning. Usual pattern: colder NW flow over the Lakes invokes broken to overcast cloud decks along with showery precipitation, downsloping over the high terrain N/W of our region, only scattered to broken decks remain with a slight chance of a shower, the greatest chance being over the Berkshires. Well- mixed lapse rates with diurnal heating, will see the mix-down of drier air and faster winds, but nothing that would appear to reach advisory level criteria. Cooler air over warmer waters, ocean-effect processes proceed, and depending on the direction of the wind, will more than likely impact the Outer Cape and Islands, especially on Saturday behind the reinforcing cold front. Will go with chance of showers at times for the aforementioned locales. Conditions overall will feel cooler given the breezy NW winds, but in actuality remain near-seasonable for this time of year. High pressure across the region over the weekend from the SW, will see a return S flow. Early next week... Consensus indications of wet-weather though the exact evolution and timing remains uncertain. With onset it is possible to see wintry mixed precipitation associated with over-running ahead of an area of low pressure emerging out of the S CONUS, especially if high pressure sets up over E Canada as some of the solutions indicate. Leaning towards an inside runner solution occluding into the E Great Lakes as a secondary low develops at the triple point and rapidly deepening offshore. Going with ensemble means but advertising low confidence. Chance PoPs for now through the remainder of the week. && .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
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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/... 115 am update... Thru 12z... Low confidence forecast. Trends for cigs and vsbys is upward as west winds mix out low level moisture. However as winds diminish toward sunrise ground fog may develop especially with dew pts in the 40s and 50s. This already taking place in the CT river valley where winds have diminished and dense fog as formed. Not expecting any improvement here until 14z/15z. Elsewhere trend upward to MVFR-VFR but have to watch ground fog to develop 09z-12z which may lower conditions back to IFR-MVFR. Worst conditions will likely be in the interior valleys and low lying locations near the coast. After 12z... MVFR-VFR however local LIFR-IFR in dense fog CT river valley and low lying sections elsewhere will improve to MVFR-VFR toward midday. Then conditions lower back to MVFR-IFR in rain 18z-21z with rain becoming steady and heavy at times from BDL-ORH-ASH and pts westward. Confidence is low on exact timing but higher on trends. Tonight... Widespread IFR with embedded LIFR in rain...heavy at times inland from BDL-ORH-ASH and points westward. LLWS possible south coast as strong southwest wind jet of 50 -60 kt moves across this region. vsbys and cigs may improve to MVFR- VFR beginning 09z- 12z Wed along with a drying trend and a wind shift to the west. Thursday... Any early MVFR cigs quickly lift to VFR along with dry conditions. Diurnal clouds yield VFR cigs for the afternoon. West winds 15 to 25 kt along with dry runways. High forecast confidence. KBOS TAF...MVFR-VFR this morning lowers to MVFR-IFR 21Z-24Z today as rain overspreads the terminal. Not expecting any dense fog this morning at Logan. KBDL TAF...LIFR in dense fog this morning likely lingers until 14z-15z then slow improvement thereafter. Outlook /Thursday Night through Sunday/... SCT-BKN low-end VFR. NW winds, blustery at times, especially along the coast with gusts initially Thursday and Friday up to 30 kts, tapering downward with time. MVFR possible over the Outer Cape with chance -RA and a breezy N wind.
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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/... 330 am update... Today... Rough seas southern waters from leftover southerly swells. Light winds become easterly and increase toward sunset today. Rain overspreads the waters late in the day. Tonight... Low pressure moves across southern New England. Southwest winds increase to 20 to 30 kt with low prob for a marginal gale /35 kt/ waters near and southeast of Cape Cod and Nantucket. Rain and fog limit vsby. Thursday... Big improvement with low pres exiting north of the region and giving way to west winds of 20 to 30 kt. This will result in improving vsbys along with dry weather. Outlook /Thursday Night through Sunday/... NW winds possibly gusting as high as 30 kts initially with a low risk of gale force, Thursday and Friday. Winds building with the wave stress. Likely to see the development of ocean-effect showers. Both wind and shower chances diminish as we go into the weekend.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Dense Fog Advisory until 9 AM EST this morning for CTZ002. MA...Dense Fog Advisory until 9 AM EST this morning for MAZ003-010- 011. RI...None. MARINE...Small Craft Advisory from 6 PM this evening to 5 AM EST Thursday for ANZ231>234-237-251. Small Craft Advisory until 5 AM EST Thursday for ANZ235-250- 254>256.
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&& $$ SYNOPSIS...Nocera NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...Sipprell AVIATION...Nocera/Sipprell MARINE...Nocera/Sipprell

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