Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231122 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 722 AM EDT Sun Oct 23 2016 .SYNOPSIS... A strong storm will move north through eastern Canada and will continue to bring gusty winds but clearing skies today. A fast moving low pressure may bring a period of light rain south of the Mass Pike late tonight and early Mon as it tracks south of New England. Dry and cool northwest flow will persist Monday afternoon through Wednesday. High pressure will drifts east of New England late Thursday followed by a front and possible showers late Thursday night into Friday. && .NEAR TERM /THROUGH TONIGHT/... 7am update... Upper lvl shortwave entering our western zones already this morning per WV imagery. This has led to the slow cutoff of both the comma head precipitation across S New england and the terrain induced rain/snows across the higher terrain of the Berkshires/Greens. The subsidence between this wave and yet another fast moving shortwave crossing the region tonight should yield some clearing across the area into the afternoon hours. Raised overall temperatures by a degree or two as we are starting warmer than most available guidance. Otherwise, current setup for winds look good, so made no significant changes to that. Previous discussion... Comma head showers continue to rotate into New Eng early this morning as mid level low moves north into Canada. Expect this activity to gradually dissipate through 12z as mid level drying begins to move in from the SW. Otherwise, clouds will give way to increasing sunshine from SW to NE through the morning into midday as this drying overspreads the region. Regarding wind, soundings show good mixing up 850 mb with low level lapse rates in this layer increasing to 8.5-9.5 C/km. 850 mb winds 45-50 kt and while we won`t mix all this to the surface in gusts, taking an average of the 850 wind and the mean wind in the mixed layer suggests occasional gusts to 30-40 kt (35-45 mph) so we will continue the wind advisory. The strongest gusts are expected over the higher elevations. 850 mb temps 0 to -2C will yield highs in the mid/upper 50s except closer to 50 degrees over the higher elevations. && .SHORT TERM /MONDAY/... Tonight into Monday... Models all show a fairly robust mid level short wave moving into SNE late tonight and early Mon with a clipper type open wave tracking south of New England. Deepening moisture ahead of the wave overspreads the region late tonight and a W-E band of low to mid level frontogenesis will combine with left exit region of the upper jet to produce an area of decent mid level forcing. There is some uncertainty with the location of the forcing and assocd rainfall but consensus of the guidance and ensemble probs suggest best chance of a period of rain south of the Mass Pike late tonight into early Mon. Will have chc pops along and south of the Pike with likely pops near the south coast. This is a quick moving system so it appears most of the precip will occur in less than a 6 hour period through 12z. The guidance is showing potential for around 0.25" within the band which may be across SNE but could also end up south of New Eng. Lingering clouds across SE New Eng early Monday will give way to increasing sunshine by midday as clearing moves in from the north. But another shortwave and strong mid level cooling moves in during the afternoon which will lead to sct-bkn cu developing, especially interior. As the wave moves to the east increasing NW winds will develop in the afternoon with gusts 25-30 mph. Highs Monday mid/upper 50s except closer to 50 over the higher terrain. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Cool and blustery through Tuesday. * Monitor for frost potential Tuesday night and especially Wednesday night. * Risk for wet weather returns late Thursday into Friday. Overview and model preferences... Labrador trof will slowly meander to the E as ridging upstream builds from the Great Lakes into New England. However, the trof maintains a constant draw of CP air across the region right through mid week leading to cool, fall-like conditions lingering. Confidence remains high in these trends as models remain in good agreement. In fact, am noting that with the 00Z update, even the next trof associated with a clipper system models are converging on a solution that suggests a passage of the sfc low to the NW by late in the work-week. While there are still a few temporal/spatial issues to work out, feel we have enough to begin using a blend of deterministic guidance as a baseline beyond the mid week period. Details... Mon night into Tue night... Blustery period following secondary wave passage early in the day on Mon. Pres gradient remains tight although the isallobaric couplet slowly shifts meridionally suggesting winds will be shifting toward the N with time. Still expect diurnal gusts to reach 25-35 mph at times, diminishing somewhat overnight, but not enough to fully realize radiational cooling. The only caveat may be Tue night, when NW valleys do decouple somewhat, allowing for temps to cool in comparison to Mon night. At any rate H85 temps drop below 0C and as low as -8C potentially Tue morning. H92 temps aren`t far behind, dropping to - 2C around the same time. Therefore, expecting overall temps below normal with highs mainly in the mid 40s to mid 50s, while lows fall into the 30s both nights. Low risk for frost Tue night, but the pres gradient may mitigate the impact, especially since the most likely locations to see frost have already seen their growing season end. Wed into Thu daytime... High pres will be moving in from the E, which allows winds to shift mainly to the N and possibly even NE by mid day on Wed. This trajectory will help to initiate ocean effect conditions as H85 temps remain near -6C with SSTs near +15C. Therefore, plenty of low-lvl instability for showers and clouds to impact portions of the Cape/Islands and even southern Plymouth county in MA until winds shift by Thu morning. Otherwise, mainly dry conditions, but with lighter winds across the interior. Highs remain similar to previous days, mainly upper 40s into the 50s on Wed, warming into the low-mid 50s. However, Wed night, good setup for radiational cooling suggests several locations could drop below freezing, including a few spots in the 20s. Will need to watch this, as frost headlines may be needed for those locations where the growing season has not ended. Late Thu into Fri... Clipper low pres with (as previous forecaster noted) a cold occlusion in process looks to pass NW of the region. Models only now beginning to agree on this solution, so although confidence grows, it is not necessarily high yet. Noting triple- point low potential which could increase the risk for precip as the fronts move into S New England early Fri. Ensembles have probabilities near 70 percent for at least a quarter inch of total precip. Therefore will be featuring POPs through this period with timing based on the more progressive GFS and slower ECMWF blend. Temperatures closer to seasonal normals as both H85 and H92 temps now exceed 0C. Next weekend... Another round of high pres follows. This particular feature looks to feature temperatures closer to normal as it is uncertain whether H92/H85 temps will drop below climatological normals. Ensemble probabilities are rather low at this time. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... Today...High confidence. VFR with skies shifting to all mainly clear by afternoon. W gusts 30-35 kt with up to 40 kts over high terrain. Tonight...Moderate confidence. Mainly VFR, but may see areas of MVFR develop south of the Mass Pike 06-12z as an area of rain moves into the region. Diminishing wind but gusty into the evening near the immediate coast. Monday...Areas of MVFR possible early SE coastal areas in lingering light rain, otherwise VFR with clearing skies. Increasing NW winds with gusts to 20-25 kt developing, strongest higher terrain. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday Night through Thursday/... Mon night through Tue night...High confidence. Mainly VFR. NW wind gusts 20-25 kt at times during the day inland, but remaining into the overnight at coastal terminals. Wed and Wed night...High confidence. VFR continues, but with lighter winds. Thu into Fri...Moderate confidence. VFR starts Thu, but a mix of MVFR/IFR possible as a front crosses the region Thu night into Fri with SHRA. Winds shift from the E, to SE, with gusts near shore approaching 25 kt at times. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High confidence. Gale force west winds with gusts 35-40 kt will gradually diminish through tonight. NW winds will increase again Mon with gusts 25-30 kt in the afternoon. Peak of the seas occurring early this morning and will slowly subside but remain above SCA through Mon. Vsbys may lower late tonight and early Mon in an area of rain, especially south coastal waters. Outlook /Monday Night through Thursday/... Mon night into Tue night...High Confidence. Winds gradually shift to the NW with time. However gusts along the waters should still reach 25-30 kt at times with seas still in the 5- 7ft range along the ocean waters. Small craft advisories continue into the evening hours Monday, at which point conditions finally recede. Wed into Wed night...High confidence. Winds and seas generally below small craft conditions although there is a low risk for a lingering swell near 5 ft which will need to be watched. Otherwise, expect widespread showers across the eastern waters. Thu intro Fri...Moderate confidence. Thu starts with conditions below small craft thresholds as winds shift to the E. However, gradual shift to the SE and increasing wind waves will yield small craft conditions by late Thu and continuing into Fri as a front approaches, then crosses the waters. Winds peak 25-30kt with seas reaching 6-8 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory until 2 PM EDT this afternoon for CTZ003>004. MA...Wind Advisory until 6 PM EDT this evening for MAZ002>024-026. RI...Wind Advisory until 6 PM EDT this evening for RIZ001>008. MARINE...Gale Warning until 11 PM EDT this evening for ANZ232>235-237. Gale Warning until 8 PM EDT this evening for ANZ230-236. Gale Warning until 2 AM EDT Monday for ANZ231-250-251-254>256. && $$ SYNOPSIS...KJC/Doody NEAR TERM...KJC/Doody SHORT TERM...KJC/Doody LONG TERM...Doody AVIATION...KJC/Doody MARINE...KJC/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.