Area Forecast Discussion
Issued by NWS Boston, MA

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598 FXUS61 KBOX 301214 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 714 AM EST Wed Nov 30 2016 .SYNOPSIS... A brief period of dry weather this morning into early afternoon before another round of soaking rain affects the region later this afternoon and into tonight. Dry conditions return Thu and continue into much of the weekend, 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 645 AM Update... Visibilities are starting to improve with sunrise, along with breaks in the low clouds at 11Z. However, conditions are still quite variable especially across the CT valley/I-91 corridor. Patchy dense fog has also developed along E coastal areas, mainly from KGHG south to Cape Cod and the islands as well as near KOWD. Will also see variable conditions in those locations through around mid morning, then should briefly improve. KBOX NE regional 88D radar mosaic showing a stripe of precip along the MA/RI/CT border to Nantucket Sound, stretching to a larger area over S central NY into central PA. No precip reaching the ground per latest OBS, even with the low temp/dewpt spreads. Expect area of precip to push eastward over the next few hours, so rain should break out by around mid morning over western areas and across the E by around midday. Will have to monitor VSBYS to see if they improve somewhat or hang between 1/2 and 1 mile. Should see slow improvement, except in any patchy heavy rainfall. Temps have fallen back across inland areas and on the coast from Cape Ann to Boston, down to the mid 30s across the inland valley of NE, N central and W Mass, ranging to the lower 50s along the S coast at 11Z. With the E-SE winds that will develop ahead of slowly approaching warm front, temps will rise again during the day. Highs should reach the 50-55 degree range for most areas, though may not quite reach 50 over the higher inland terrain. Have updated near term forecast to bring conditions current. Previous Discussion... 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. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... 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. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Dry pattern in place through most of the upcoming weekend with a cooling temperature trend * Low pressure may bring a wintry mix of precipitation late this weekend into early next week Overview... Cutoff mid level low pres over Quebec and northern New England to start off the period will slowly shift into the Maritimes to Labrador. Drier air will rotate around the base of this low, though noting a couple of weak short waves that may pass close to central and northern areas this week. However, they lack moisture, so not a lot of precipitation is expected. A general W-NW wind flow will continue through this weekend, which means a dry pattern. Noting slowly falling H5 heights, so temperatures will also trend cooler. The big question remains as to the evolution of cutoff H5 low pressure across the SW U.S. and its progression across the lower 48. At this point, models and ensembles signaling some of the moisture shifting NE over the weekend, then may push toward the region around the Sunday night-Monday timeframe. Some moisture tap from the Gulf, though models showing solution spread with this aspect. The storm track does remain progressive, though the exact track is still in question, as some keep the bulk of the moisture S of the region. With cooler air in place at the onset, could see a wintry mix before eventually mixing/changing over to rain during Monday. Still quite a bit of things to settle on with this system. At this point, should dry out for Tuesday. Details... Thursday night through Sunday... Expect mainly dry conditions through this timeframe as cutoff mid level low pressure remains over Quebec early, then slowly shifts E through the weekend. Some question as to a weak short wave that may slip SE across the region late Fri into Fri night, which might bring some brief mixed precipitation across the E slopes of the Berkshires. Have slight chance to low CHC POPs mentioned, but rather light on the QPF so not much in the way of accumulations expected. Temperatures will run around 5 degrees above seasonal normals for early December on Friday, then cooler air with lowering H5 heights moves in during the weekend. This may trigger some ocean effect showers across outer Cape Cod late Fri night through Sat night, but again will be light and spotty. Should be mostly sunny for most areas during Sunday as a weak high pres ridge crosses the region. Temperatures will run a few degrees below normal. May start to see high clouds move in to western areas during the afternoon. Sunday night through Tuesday... 00Z model suite showing general agreement with developing low pressure across the southern stream Sunday night. However, its track as well as how much of the moisture associated with the low will push into the region is very much in question. Progressive H5 trough looks to push steadily E late Mon/Mon night, so any precipitation should move through quickly. Another big question will be PTYPE with the onset of the precip as it moves in. Will be cool enough at the surface, but the thermal pattern through the column will be the wild card for how much mixing takes place as well as how long it lasts late Sun night into Mon morning. May also have issues with wind shift to S-SE, which would allow milder air to work in and bring a change to rain during Mon. This will be dependent upon whether the low shifts closer to the region or not. At this point, with the progressive nature of this system, should see drying conditions as high pressure builds out of central Canada. However, timing is still in question so lower confidence during this timeframe continues. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... 7 AM Update... Today... Areas of LIFR-IFR CIGS/VSBYS in dense fog across the CT River valley and along portions of E coastal areas, Cape Cod and the islands at 11Z. Conditions should slowly improve toward midday. Will see areas of IFR conditions in rain 18z-21z with rain becoming steady and heavy at times from BDL-ORH-ASH and points 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. CIGS/VSBYS may improve to MVFR-VFR beginning 09z-12z Thu 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/... Thursday night-Friday night...Moderate to high confidence. Mainly VFR, though low end SCT-BKN at times across central and western areas. May see brief periods of sct -SHRA/-SHSN across the E slopes of the Berkshires, with the best chance late Fri/Fri night. May see local MVFR CIGS with isold -SHRA across outer Cape Cod late Fri night. W winds gusting up to around 20-25 kt during Friday, possibly up to 30 kt along the immediate S coast. Saturday-Sunday...Moderate confidence. Mainly VFR. Slight chance for -SHRA across outer Cape Cod Sat-Sat night. NW winds gusting to around 20 kt along the S coast Saturday into early Saturday night. && .MARINE... 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. Small crafts continue for all waters except Boston Harbor and Narragansett Bay. 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/...Moderate confidence. Thursday night-Friday...W winds gusting up to 25-30 kt with seas 5-9 ft, highest across the southern outer waters. Friday night through Sunday...NW winds gusting up to 25 kt through Saturday, then slowly diminishing. Seas remain AOA 5 ft through Sat, then should subside. Scattered ocean effect showers likely developing from time to time Fri night through Sat night. && .BOX WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera/EVT SHORT TERM...Nocera LONG TERM...EVT 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.