Area Forecast Discussion
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000 FXUS61 KBOX 230815 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 315 AM EST Thu Feb 23 2017 .SYNOPSIS...
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High pressure centered offshore southeast of New England will bring dry and unseasonably warm conditions today and tonight. A cold front stalls over Southern New England tonight and then moves north as a warm front Friday. A strong cold front will cross the region late Saturday afternoon and night, bringing areas of rain and patchy fog. There will be a low chance for isolated thunderstorms as the front passes. Near seasonable temperatures will return early next week, with blustery conditions on Sunday and Monday. There may be another chance for precipitation around the middle of next week.
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&& .NEAR TERM /THROUGH TODAY/...
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High pressure centered offshore is bringing a light southwest flow to the region. This moved higher dew point air onshore along the South Coast and brought low clouds and dense fog to the region. After sunrise the clouds and fog should retreat out over the water. A Dense Fog Advisory will continue along the South Coast of RI and MA through the morning rush hour. Low pressure passes across Ontario and Quebec today, while the high pressure remains just offshore. This will create a better defined gradient to aid southwest winds. A 50 knot southwest jet is expected to move up the St Lawrence Valley, while a secondary southwest jet will move across Srn New England at 2000-3000 feet. Speeds in the secondary jet are forecast at 30-35 knots, and may spin up gusts of 20-25 knots at the surface. Warm advection in the southwest flow should limit the mixing depth, but temps at 925 mb reach 9-12C which would support max sfc temps in the lower 60s, roughly 60-64. If we mixed all the way to 850 mb we would tap 7-8C, which would support max sfc temps in the lower 70s. A mixed layer up to either 950 or 925 mb looks more reasonable. The southwest flow off the ocean should keep readings cooler along the South Coast. Ocean temps are in the low 40s, so daytime highs should be in the upper 40s and lower 50s. Note the Climate section at the end of this discussion. Based on expected temps, PVD and ORH stand a chance of tying/breaking the max temp record today. BOS has an outside chance, but we think they will fall just short. BDL would need to mix above 900 mb to have a chance, and this would seem too much.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM FRIDAY/...
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Tonight... Cold front trailing the Canadian low will drift into or near Southern New England tonight, but becomes parallel to the upper flow by midnight and should stall by that time. Digging shortwave over the Plains will eventually turn the upper flow more southwest and push the stalled front north as a warm front. Although placement of the front when it stalls will determine our overnight weather, it seems likely that most of our area will remain south of the front...certainly the areas south of the Mass Pike. This will mean another night of moist air with fog and low clouds again moving ashore from the south. Dense fog may again be a concern overnight. Dew points in the 40s point to min sfc temps in a similar range. Friday... Cold front slowly lifts north of our area during the day. Southwest flow will increase through the day, eventually generating lift across the front and resulting in light rain or showers. The best chance of this will be in areas north of the front, northern MA. Clouds will work against similar temps to Thursday. But temps at 1000 mb continue to support max sfc temps near 60. The southwest flow will again work to keep south coast areas several degrees cooler.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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Highlights... * Front shifts north of the region late Fri/Fri night with scattered showers * Areas of drizzle and patchy fog Fri night/early Sat * Mild with widespread areas of rain Sat into Sat night * Dry, blustery and cooler Sun/Mon Overview... 12Z models suite continues showing a good overall handle on the surface and upper level features even in the progressive flow aloft through the weekend. Timing and track differences with individual features work in from about Monday onward, especially with a possible system that may pass near or S of the region around the late Monday/Monday night timeframe. Another front may try to approach around Wednesday, but again with fast flow across the northern stream, low confidence with the timing and track of this system. Details... Friday night... SW flow at the surface and aloft ahead of approaching strong cold front and H5 cutoff low pres will slowly shift E Fri night. Will see areas of drizzle and patchy fog along with lingering showers in the moist low level flow. Saturday... Cutoff H5 low shears N-NE into western Quebec late Saturday, but remaining strong short wave will shift E Sat night. Surface front will quickly push E across the region. Short range models, specifically the 12Z NAM, signaling quite a bit of instability with and ahead of this front, including LIs near zero, total totals from 50-54, Showalter index of -2 to -3 and TQ values around 20. Also lapse rates on order of 7C/km or higher at about H7 at both KALB and KBDL Sat evening, and up to 8C/km at KORE overnight. However, noting some mixed signals. BUFKIT soundings showing several saturated soundings until just before the instability moves in, with the best shot across the E slopes of the Berkshires as well as the CT valley region. Strong low level jet will move across as well, with forecasted speeds on order of 50 kt at 3kft at both KBDL and KBAF and 52 kt at 2kft at KALB. Again, though, there is capping in place so will have to see if the cap can be broken. Will be most difficult along the S coast where the marine layer could keep conditions more stable. A lot to consider, but have put slight chance of thunder back in the forecast for all areas, as large area of TT in the lower 50s crosses the region. Looks like best chance of thunder will occur between 22Z and 05Z. But, if the convection does indeed get going in the vicinity of the strong low level jet, could see some gusts with any thunderstorms. They will be few and far between, though. Feel the best shot for thunder will occur across central and western Mass into N Central CT. Also noting a band of moderate to heavy rainfall crossing ahead and with the front. QPF amounts from 0.25 to 0.5 inches, with highest amounts across the E slopes of the Berkshires. If this does materialize, could help mix some of the strong winds down as well even without any convection. Generally east of a KFIT- KORH-KIJD line, precip will be lower as the front will tend to speed up as it crosses the region. As the front pushes across, temps will drop quickly behind it. The back edge of the precip will quickly follow, but could see some mix of change over to snow across the higher inland terrain before ending. At this point, may see the light snow around or after midnight for a few hours before ending. A few snow showers may linger across the higher terrain of NW Mass. Sunday and Monday... Expect dry and seasonable conditions for Sunday, but blustery NW winds will make it feel much cooler. Expect gusts up to around 25-30 mph with excellent low level mixing in place, especially across the higher terrain and along the coast. Will see temps reach the mid and upper 40s across the coastal plain, but holding in the mid 30s to around 40 across the higher terrain. With the cooler temps and gusty winds, wind chill values may be below 20 degrees across the E slopes of the Berkshires, and in the mid 20s to lower 30s elsewhere. On Monday, high pressure ridge pushes offshore as fast progression of weather systems continue. SW winds increase, with gusts up to around 25-30 mph possible, highest across the higher terrain and along the S coast. Questions on timing and track of passing low pressure system late Mon or Mon night. 12Z GFS/ECMWF has fairly good agreement in keeping most of moisture S of the region, but could see some widely sct showers as it moves across. Not a lot of confidence with the evolution of this system, however. Tuesday-Wednesday... Leaned toward a blend of the 12Z GFS/ECMWF along with their ensembles during this timeframe, showing a bit better agreement with timing and track of fast moving systems. Low pres should push offshore S of New England Tuesday morning, taking any leftover showers with it. Big questions surface with yet another system moving across the northern stream during the Tuesday night/Wednesday timefr Thursday and Thursday night... Wind speeds Thursday increase some as winds strengthen aloft. This might be enough to bring gusts 20-25 kt to the coastal waters Thursday afternoon. Seas may approach 5 feet on the outer waters Thursday afternoon/evening. Friday...Low confidence. Southerly flow will switch to a more northeast to east flow during the day. Vsbys restriction possible in fog and drizzle especially across the southern waters.ame. 12Z Canadian Global GEM was most aggressive with this low, likely due to its associated cutoff H5 low, while the GFS and ECMWF kept a more open H5 wave with it. Does look like this system should pass across the Great Lakes, but wide variance on timing and track of this feature keep rather low forecaster confidence.
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&& .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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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 Friday/... Today...Moderate confidence. IFR and LIFR cigs/vsbys along the South Coast and Islands, while VFR conditions farther north. Patchy MVFR vsbys possible in patchy fog before sunrise away from the coast. The south coast fog will retreat offshore this morning, with all areas becoming VFR. Tonight...Moderate confidence. Low clouds and fog will again move ashore along the South Coast and Islands. Expect conditions to return to IFR/LIFR in fog. Potential for MVFR and patchy IFR in lighter fog farther north. Friday...Low-Moderate confidence. A cold front will stall over Southern New England by Friday morning and then slowly lift north. Still quite a bit of uncertainty as to where this will stall. Expect IFR cigs and MVFR vsbys in morning fog. Areas of MVFR cigs/vsbys expected in showers Friday afternoon near or north of the front...so the best chance for this would be in Northern MA. KBOS TAF...Moderate confidence in TAF. KBDL TAF...Moderate confidence in TAF. Outlook /Friday Night through Monday/... Saturday...Moderate confidence. Should see widespread MVFR-IFR conditions as rain moves in across the region. May see areas of LIFR CIGS develop Sat afternoon/night along the coast and interior higher terrain. Low chance for isolated thunderstorms from 21Z Sat to 04Z- 05Z Sun as cold front passes. May see period of light snow after midnight Sat night across higher inland terrain as precip tapers off. Sunday...Moderate confidence. Conditions rapidly improve to VFR by mid morning Sun. W winds gusting to 25-30 kt, highest across the higher terrain and along the coast. Monday...High confidence. Mainly VFR conditions. A low chance for showers south of the Mass Pike as weak low pressure passes S of New England. Low chance for brief MVFR conditions in any showers. W winds gusting to around 25 kt during the late morning and afternoon across the higher terrain and along the coast.
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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 Friday/...High confidence. Today... Areas of dense fog will linger through mid morning and then shift farther offshore. This means poor vsbys early, but then improving. Southwest winds will increase today with gusts of 20 to 25 knots, especially on the Eastern outer waters. Seas remain below 5 feet. Winds will need to be monitored, but currently look to remain below Small Craft thresholds. Tonight and Friday... Cold front moving south will stall overnight or Friday morning, then move slowly north. The Massachusetts North Shore may spend a few hours north of the front with winds shifting from the east or southeast. Areas south of the front will maintain southwest winds through the period. Thursday and Thursday night... Wind speeds Thursday increase some as winds strengthen aloft. This might be enough to bring gusts 20-25 kt to the coastal waters Thursday afternoon. Seas may approach 5 feet on the outer waters Thursday afternoon/evening. Friday...Low confidence. Southerly flow will switch to a more northeast to east flow during the day. Vsbys restriction possible in fog and drizzle especially across the southern waters. Diminishing southwest winds will be less than 25 knots. Seas near 5 feet on the eastern outer waters and less than 5 feet elsewhere...with a subsiding trend overnight. Offshore fog and low clouds will move ashore again tonight and linger into Friday morning. This will bring a period of poor vsbys in fog and drizzle during this time. Outlook /Friday Night through Monday/... Saturday...Moderate confidence. Increasing southerly flow with the potential for SCA gusts. Waves will also increase in response. Vsbys reduced in developing rain and fog. Sunday...High confidence. Northwest winds will keep seas up and increase wind gusts near 30 kts. Low probability for gales across the outer waters.
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&& .CLIMATE... Record Highs for Thu Feb 23 BOS...65/1990 BDL...68/1990 PVD...60/1990 ORH...61/1990 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Dense Fog Advisory until 9 AM EST this morning for MAZ020>024. RI...Dense Fog Advisory until 9 AM EST this morning for RIZ006>008. MARINE...None.
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&& Thursday and Thursday night... Wind speeds Thursday increase some as winds strengthen aloft. This might be enough to bring gusts 20-25 kt to the coastal waters Thursday afternoon. Seas may approach 5 feet on the outer waters Thursday afternoon/evening. Friday...Low confidence. Southerly flow will switch to a more northeast to east flow during the day. Vsbys restriction possible in fog and drizzle especially across the southern waters. $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB SHORT TERM...WTB LONG TERM...EVT AVIATION...WTB/EVT MARINE...WTB/EVT CLIMATE...

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