Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 232113 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 413 PM EST Thu Feb 23 2017 .SYNOPSIS... High pressure offshore of New England will bring unseasonably warm conditions into Saturday. A warm front may trigger a few showers across northern Massachusetts tonight and Friday morning, with light spotty drizzle elsewhere. Otherwise mainly dry weather prevails until a strong cold front brings some heavy showers late Saturday afternoon and evening. There will be a low chance for isolated thunderstorms as the front passes. Near seasonable temperatures return Sunday into early next week along with blustery conditions. There may be another chance for precipitation around the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 410 PM Update... Well after a record setting day of warm temperatures (BOS 68, PVD 66, BDL 66 and ORH 64) a very pleasant early evening is ahead with warm temps and winds diminishing. However our attention quickly turns to low clouds and patchy fog along the south coast that continues to dissipate. This trend will continue into early this evening but as the blyr continues to cool this low level moisture is likely to return in the form of low clouds and fog later tonight. However couple of wildcards here...1) additional area of low clouds and fog upstream along the south coast of Long Island that continues to advect northeast toward Block Island and RI south coast. 2) second wildcard is SC/CU clouds over to the west across PA and NY. Models have this lifting into a mid deck of clouds and overspreading our region later this evening and overnight. This may help keep temp up a bit and large enough dew pt depressions to preclude low clouds and fog becoming widespread. Nonetheless the trend tonight will be for mainly clear skies to become mostly cloudy. Frontal boundary to the northwest of SNE may bleed southward tonight but then lift north as warm front late tonight. This may be sufficient for some spotty light rain especially across northern MA. Elsewhere mainly dry conditions likely prevail other than some spotty light drizzle overnight. Will remain in the warm sector so a very mild night ahead with lows in the 40s...more typical of our daytime highs for late Feb. Given dew pts are in the 40s (AOA our normal daytime highs), as mentioned above expect at least patchy fog to develop as the night progresses. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Updated 410 PM... Friday... Warm front across northern MA in the morning lifts slowly north. Thus at least some sunshine across CT/RI and southeast MA with more clouds across northern MA especially in the morning. This boundary may yield some spotty light rain over northern MA in the morning along with spotty light drizzle elsewhere, but the trend will be towards drier weather for the afternoon. Given we`ll remain in the warm sector expecting another day of highs in the 60s across CT/RI along and south of the MA pike. Route 2 corridor northward to the VT/NH border will be slightly cooler with highs in the upper 50s given cool side of the boundary. Boston and the north shore may have seabreezes that limit highs to the 50s. However let`s keep in mind it`s still late Feb when normal daytime highs should be only in the lower 40s. Thus spring fever continues and 60s possibly lingering into Sat too! Friday night... More of the same, warm sector airmass remains over the region so very mild conditions prevail with temps only falling into the 40s along with another round of patchy fog and drizzle. && .LONG TERM /SATURDAY THROUGH THURSDAY/... 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 /21Z THURSDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... 410 PM update... Thru 00z...mainly VFR with patchy IFR along the south coast in low clouds. Some uncertainty how quickly these low clouds and fog redevelop. SSW winds gusting near 25 kt will dissipate by sunset. After 00z...low confidence forecast with lots of uncertainty on how quickly IFR-LIFR conditions redevelop. VFR to start the evening but patchy IFR conditions along the south coast will redevelop 03z-06z and then expand northward, although forecast confidence is very low on its evolution. Patchy drizzle may accompany these low clouds as well with low risk of a few light spotty showers northern MA late. Friday...moderate confidence. Combination of IFR-MVFR in the morning with slow improvement to from south to north. Low risk of some spotty light rain across northern MA. Friday night...MVFR likely with light spotty showers/drizzle possible. KBOS TAF...high confidence until about 00z then diminishing tonight and thereafter. KBDL TAF...high confidence until about 00z then diminishing tonight and thereafter. Outlook /Saturday through Tuesday/... 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. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. Other than some gusts near 25 kt early this evening near shore, SSW winds will be fairly light along with small seas. Biggest concern will be vsby lowering to below a mile a times in patchy fog tonight thru Fri night. Outlook /Saturday through Tuesday/... 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...Dunten AVIATION...Nocera/Dunten MARINE...Nocera/Dunten is the U.S. government's official web portal to all federal, state and local government web resources and services.