Area Forecast Discussion
Issued by NWS Boston, MA

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900 FXUS61 KBOX 221403 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1003 AM EDT Sat Oct 22 2016 .SYNOPSIS... A strong upper level disturbance moving into New England will bring an area of rain today. In addition, strong west winds will develop late today and continue into Sunday as a strong storm settles over the Maritimes. A cold front may bring a few more showers Sunday night, then dry but cool conditions persist into midweek. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 am update... */ Highlights... - Pivoting N/E area of rain, embedded heavier showers - Rainfall amounts up to an inch possible, mainly N/W SNE - Low risk flooding issues - Increasing winds and cold air advection into evening - Gusts up to 40 mph possible - Wind advisory posted, mainly event-driven with leafed trees */ Discussion... As alluded to earlier, a negatively trof lifting N and E across the NE CONUS is the main focal point to todays weather. Fair amount of dynamically driving mechanisms of low to mid level forcing per potent mid-level vortex, frontogenesis, and trowaling moist-convergence beneath favorable venting and diffluence aloft (strong QG forcing in other words). Outcomes apparent with pivoting NE moving rainshield over E PA / NJ into the Hudson River Valley into Upstate NY. Colder air rushing in at multiple levels parent with the leading edge of drier air within the latest water vapor satellite, an emphasis on some measure of instability which invokes at least a rumble of thunder but will hold off on a mention in the forecast grids. Embedded heavier areas of rain, could see rainfall amounts up to 1 inch with the focus of higher confidence over N/W portions of S New England especially across the higher terrain. Monitoring closely areas that are already swollen from overnight rainfall, but have an overwhelming sense that the region can handle it. Comes down to leaf-clogged drains and whether they allow rain water to drain. Likely to definite PoPs. Following closely with a consensus of high-res near-term guidance which seems to handling the situation well enough. Likely some visibility issues with areas of heavier rain at times. Towards evening, cold and dry air moving in progressively from the W behind the negatively-tilted trough. Surface low deepening to 980 mb as it lifts NE through Maine into the Saint Lawrence River Valley. Tightening pressure gradient and isallobaric component of flow as the boundary layer mixes out to H9. Will see H925 winds on the back side of the system increase to 40 kts with the environment favorable for mixing such momentum down to the surface. Accompanying drier air, visibilities improve. May still be a stubborn low deck of clouds through morning by which point it should clear out. Gusts up to 40 mph valid. May not happen for all areas within the advisory but rather the advisory is event-driven given that trees are still fully leafed. Likely to see some down branches, trees, overall issues that will lead to isolated-scattered power outages. Strongest winds across the high terrain, along the immediate milder coastlines, and over the warmer waters. Winds going through the overnight period. Given cold air advection continuing, do not believe the boundary layer will stabilize to limit mix-down of faster momentum. Temperatures falling throughout much of the day. Warmest conditions presently ongoing but should drop out from under as winds out of the W and cold air advection and gusty winds increase with time. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Tonight... As mid level low lifts into northern New Eng, comma head moisture will rotate into SNE with additional shower activity possible, especially in the interior where deeper moisture is present. Strong gusty winds will be the main concern tonight as low pres deepens as it moves north into the Maritimes. Soundings support gusts to 40 mph at times so we will issue a wind advisory for MA/RI as trees are still close to fully foliated making it easier to sustain tree damage. The wind advisory will likely be expanded to include CT in later forecasts. Low temps will range from upper 30s to mid 40s. Sunday... Some clouds will linger into the first part of the morning, but clearing will quickly develop from SW to NE as excellent mid level drying moves in leading to a mosunny day. Strong winds will continue to be a concern with a secondary surge from excellent mixing. Soundings support gusts to 35-45 mph with up to 50 mph gusts possible over higher elevation in central and western MA. Highs will be in the mid/upper 50s, cooler higher terrain. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... */ Highlights... - Cooler and dry Sunday into midweek. */ Overview and model preferences... Have reasonably high confidence in overall trends through the mid term, and much of the extended term as the 00Z guidance update continues to show good agreement. Labrador cutoff will slowly deamplify and shift to the northern Atlantic, but the attendant trof remains in place across the region yielding a draw of CP air across the area. This suggests a mainly dry but cool period through much of the week, with the dryness thanks to building ridge upstream. A lee low pres and trof (clipper-type system) will move off the Rockies during the late week period, and models disagree on its interaction with the aforementioned ridge. Therefore, although there will be a risk for more unsettled weather by Fri or the weekend, the timing and ultimate impacts are a question-mark at this time. Given there is reasonably good agreement between models, a blend of deterministic guidance with persistence will be used for this update. */ Details... Sun night into Mon... Reinforcing, fast moving shortwave, will be sliding quickly across the region early Mon morning. There is a risk for a few shra with this passage as low lvls from the sfc to about H7 do saturate and feature modest lapse rates thanks to cold advection aloft. Pops will be caped at low end chance. Otherwise, isallobaric couplet shifts backing the winds to the NW, so the breezy conditions are expected to continue into Monday. H92 temps drop to near +2C by late Mon, so highs will remain in the 50s. Sun night mins will remain higher than they could be due to the continued strong pres gradient, looking at mainly upper 30s to mid 40s. Mon night into Tue... Radiational cooling expected Mon night as H92 temps continue to drop below 0C. Will likely see widespread temps in the low-mid 30s and even a few upper 20s possible in the NW valleys. Will need to monitor for some frost/freeze headlines where the growing season continues. The fall-like conditions continue Tue, although less windy with highs mainly in the upper 40s to mid 50s. Wed and Thu... Dry wx lingers as high pres moves across the region, but as it approaches, winds continue to back to the N and possibly even NE. Therefore, could be a caveat to the dry conditions for the Cape/Islands and southern Plymouth county. Noting H85 temps averaging about -6C with SSTs remain near +15C, yielding a delta-T of 21C or more. Therefore, will need to watch for ocean effect clouds and showers across these areas. Otherwise, cool mins in the 30s with highs in the 50s are expected each day, combined with diurnal cloudiness. Fri and Sat... Overall forecast becomes more uncertain due to interaction of a trof from the lee of the Rockies and its interaction with ridging across the northeast. Periods of rain, or at least more unsettled weather are possible, but timing and final totals will take more time to nail down, especially since the trof that triggers the weather has yet to even form at this time. && .AVIATION /13Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/... 14z major changes to the forecast. Today...Moderate confidence. IFR/LIFR through morning with gradual lifting of CIGS into afternoon to MVFR. Areas of -RA sweeping N/E through the day with localized RA/+RA mainly over N/W as well as central portions of S New England. Low risk of an isolated TSRA. Increasing W winds into afternoon with gusts 25-35 kt developing, especially south of the Mass Pike. Tonight...High confidence. MVFR cigs improving to VFR. SCT SHRA continuing, but becoming less, mainly N/w New England and focused over higher terrain. W wind gusts to 35 kt. Sunday...High confidence. VFR cigs clearing in the afternoon. West wind gusts 30-40 kt, strongest higher terrain. KBOS TAF...High confidence in trends but lower confidence in details. KBDL TAF...High confidence in trends but lower confidence in details. Outlook /Sunday Night through Wednesday/... Sun night through Tue...High confidence. VFR. W winds remain elevated (shifting somewhat to the NW Tue). Daylight winds gust 20-30 kt at times and then subside during the overnight hours except at terminals along the immediate coast. Wed and Thu...Moderate confidence. Mainly VFR, although some MVFR conditions possible mainly over the Cape/Islands and southeastern Massachusetts. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...High confidence. 10 am major changes to the forecast. Gale force westerly winds will develop mid/late afternoon southern waters expanding across the rest of the waters by early evening. Gusts to 35-40 kt expected which will persist into Sunday. Gale warnings continue. Vsbys will improve later this morning and early afternoon. Outlook /Sunday Night through Wednesday/... Sun night...High confidence. Remnant westerly gale force winds will recede to between 25-30 kt. So Gale warnings will give way to small craft advisories. Seas remain elevated 5-7 ft. Mon through Tue...High confidence. Persistent W winds with gusts 25-30 kt and seas 5-6ft. Small craft advisories likely last both days. Wed and Thu...Moderate confidence. Winds shift to the NW then N. Some gusts, especially late Wed night into Thu may approach small craft advisory thresholds. Seas may briefly dip below 5 ft but secondary swells may exceed 5 ft by Thu. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory from 8 PM this evening to 2 PM EDT Sunday for CTZ002>004. MA...Wind Advisory from 8 PM this evening to 2 PM EDT Sunday for MAZ005>007-013>024. Wind Advisory from 8 PM this evening to 6 PM EDT Sunday for MAZ002>004-008>012-026. RI...Wind Advisory from 8 PM this evening to 2 PM EDT Sunday for RIZ001>008. MARINE...Gale Warning from 2 PM this afternoon to 6 PM EDT Sunday for ANZ232>235-237-255-256. Gale Warning from 5 PM this afternoon to 6 PM EDT Sunday for ANZ230-231-236-250-251-254. && $$ SYNOPSIS...KJC/Doody NEAR TERM...KJC/Doody/Sipprell SHORT TERM...KJC LONG TERM...Doody AVIATION...KJC/Doody/Sipprell MARINE...KJC/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.