Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231509 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1009 AM EST Thu Feb 23 2017 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 AM Update... *** Record Highs Likely This Afternoon *** Tricky forecast for southern RI and MA with low clouds and fog continuing to burn off at mid morning but more low level moisture across Long Island eastward to Block Island and spreading ENE. Unfortunately none of the latest guidance is completely capturing this second batch of low clouds and fog upstream. Thinking is given low level winds will remain from the SSW this afternoon combined with chilly near shore water temps in the low 40s along with low Feb sun angle, low clouds and fog will move back into the coastal RI and MA by midday. However given sunshine have boosted temps into the 50s along the south coast already, this should thin/erode upstream fog just enough to preclude widespread dense fog this afternoon across the south coast. So while there will be widespread fog here visibilities should be half mile or greater with second round of fog. SSW pressure gradient does increase this afternoon so PVD wind should flip from SE to SSW this afternoon and give them a new record high. Given this warmer scenario leaning toward the warmer EC mos with highs 65-70 across interior CT-northern RI into much of northern MA including the Greater Boston area. Worcester area just a bit cooler given elevation but still 60-65 likely. These warmer temps are supported by SPC mesoanalysis depicting +13C airmass at 925 mb over the region this morning. SSW pres gradient and sunshine should promote mixing to 925 mb across the interior. Adding 8C to the 925 mb temps (+13C) supports highs 65 to 70 across northern CT/RI and MA including the greater Boston area. See climate section below for records and forecast highs today. So other than increasing temps and adjusting cloud cover previous forecast remains on track.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... 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. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Mild with widespread showers likely Sat into Sat night * Blustery and cooler Sun/Mon * More active pattern for next week Pattern Overview... 00z guidance is in general agreement synoptically, still have some several mesoscale features to resolve. Synoptically potent Plains trough will move towards New England on Saturday pushing a cold front through by Saturday night. Chilly and blustery conditions for Sunday and Monday as zonal flow takes shape. Guidance diverges beyond Sunday leaving a low confidence forecast. Zonal flow to start but the GFS is more progressive and develops a quick moving system on Monday while the EC is dry until Tuesday. Timing issues need to still be resolved. Next system to watch is Wednesday/Thursday timeframe but model sensitivity to this system is high as the EC is more progressive than the GFS. Regardless, looks like precip during the mid-week with cooler temperatures once again by Thursday. Trended the next weeks forecast towards a blend of the Ensembles as well as the EC which appears to be inline with the UKMET. Details... Saturday into Saturday night... Potent shortwave will move through the flow and approach southern New England on Saturday. This wave will drag a cold front across the region ending the chances for above average temperatures. During the morning, appears to be enough low level moisture trapped under an inversion to keep low clouds and drizzle across a portion of the area. Highest confidence is across the south coast, but this area can be greater as surface southerly winds will continue to advect higher dewpoint into the region. Ahead of the front, anomalous southerly flow with LLJ increasing to 35-45 kts as 925 mb temps warm to 11C. This will result in above average temperatures for the region as well as gusty winds. PWAT values also increase near 2 STD above normal as southern stream moisture is fed into the system. Along the front, a secondary low will develop but appears it will be to far north and east and will to keep southern New England out of the heavy qpf. This appears to be inconjunction with the GEFS as well as the EC Ensembles which has just a 20 percent prob of qpf over 0.5 inch. Will need to continue to watch this secondary low and see where it will eventually develop during this system. Otherwise appears that the bulk of the heavy precip will be across upstate NY and VT including the east slope of the Berks. This area is where the better dynamics will be as well as enhancement due to upslope. May need to watch river levels after this system because of the heavy rainfall potential and snow melt up north. Right now ensembles are pointing towards a few sites near action stage. As the cold front approaches, does appear that profiles turn moist adiabatic. This may help mix some of the higher winds to the surface. So cannot rule out a few gusts above 40 MPH. Also guidance continues to show some elevated instability with TT above 50 and LI below 0. Because of the steep pressure falls with this system, cannot rule out the potential for a rumble of thunder and have continued to mention the potential in the forecast. FROPA will be quick as temperatures plummet behind the front. Could see some wet flakes on the backside depending on how much moisture is left as front moves through. Right now cannot rule out an inch across far NW Mass. Sunday into Tuesday... Chilly and blustery NW flow will take over the region by Sunday into Monday. Temperatures difference between Saturday and Sunday could be close to 15-20F. Wind gusts could also increase close to 30 MPH as the region mixes well above 850mb. This will result in wind chill values in the 30s. A stark contrast from the previous several days. Guidance mesoscale issues come to light by Monday as a weak wave appears to move through the flow. 24 hour timing difference between the GFS and EC with the EC pushing the system through on Tuesday. The latest ECENS and GEFS are leaning closer to the EC keeping the high pressure over the region on Monday. However there are still a few members that are on the fast side. Whether this system comes in on Monday or Tuesday we could see some rain/snow showers for the region. Low confidence on timing. Wednesday and beyond... Large spread in the guidance for this period. Synoptically mean upper level ridge over the Atlantic will help temps warm above average. However potent shortwave moving through the Great Lakes will push a warm and cold front towards southern New England. A lot of issues to be resolved in exact placement of the low and if any secondary low pressure systems develops. But right now models are in agreement on the timing with this system coming through Wed PM/Thursday with another cold snap behind it. && .AVIATION /15Z 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/... 10 am update... Challenging forecast along the south coast of RI and MA as IFR/LIFR conditions in low clouds and fog move back into the area this afternoon from the southwest. Should see VFR along and north of a PVD- TAN- GHG line this afternoon. Previous discussion below... 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. Fog and Drizzle to start the day in MVFR/IFR conditions. Potent cold front will move through Sat PM brining heavy rain, gusty winds near 30 kts and the potential for thunder. Behind the front could see some wet flakes across the NW terminals. All of this could drop conditions to IFR/LIFR overnight, but anticipate a rapid improvement near dawn Sunday. Sunday...Moderate confidence. Improving conditions with blustery NW wind gusts near 30 kts. Monday...Low confidence. Still a large spread in guidance. Mainly VFR conditions with NW gusts near 25kts. Could see some sct showers across the south 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. 10 am update... Low clouds and fog burning off around Cape Cod waters at late morning. However new area of fog moving across Long Island into Block Island. This will spread east across all the southern waters this afternoon, although vsby not as poor as earlier this morning...mainly 1/2 mile or greater. Previous discussion below... 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. 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. Low potential for thunder late in the day. Sunday...High confidence. Northwest winds will keep seas up and increase wind gusts near 30 kts. Low probability for gales across the outer waters. Monday...Low confidence. Large spread in the guidance but gusty NW winds will continue keeping seas up for sometime.
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&& .CLIMATE...
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Updated 10 am... Record Highs for Thu Feb 23 BOS...65/1990 BDL...68/1990 PVD...60/1990 ORH...61/1990 Forecast Highs for Thu Feb 23 BOS...65 BDL...69 PVD...63 ORH...63
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Dense Fog Advisory until 11 AM EST this morning for MAZ021-022. RI...None. MARINE...None.
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&& $$ SYNOPSIS...WTB/Dunten NEAR TERM...Nocera SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Nocera/Dunten MARINE...WTB/Nocera/Dunten CLIMATE...Nocera

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