Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 221120 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 720 AM EDT Sat Oct 22 2016 .SYNOPSIS... A strong upper level disturbance moving into New Eng will bring numerous showers 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 mid week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7am update... Focal point now becomes strong inverted trof generated within the wrap-around trowal of the sfc low pres moving into New England and continually deepening. At the same time, upper level potent shortwave moving into meet it as it becomes negatively tilted. All this spell good dynamics for another area of rainfall which will pivot slowly from W-E across the region through the morning and early afternoon. High K-values and TT suggest pockets of heavy rain, although likely not as widespread as it was last night. Overall new totals may exceed an inch or so in spots, but this would be highly localized. Latest meso-scale guidance such as the WRF and HRRR are focusing in on timing, so POPs were adjusted to match their thinking. Otherwise, dry air progressively works in from the W along with strong impulse which will induce strong winds through the afternoon. Current timing/setup for wind advisories look good, so no plans for changes there. Previous discussion... Potent negative tilt trof and mid level low will move NE across New Eng this afternoon and evening. Deepening moisture ahead of the trof combined with strong QG forcing will result in numerous showers moving east across the region this morning into early afternoon. The showers should then become more focused across the interior late this afternoon as a dry slot tries to move up along the coastal plain. Impressive mid level cooling will add an element of instability so brief heavy rain is possible in some showers and can`t rule out an isold rumble of thunder. In fact, much of the hi-res guidance is suggesting localized rainfall of 0.50 to 1 inch is possible in the interior. As cold front moves across the region, expect falling temps in western New Eng through the 50s and into the 40s this afternoon. In the coastal plain, temps will be in the 60s this morning before dropping through the 50s through the afternoon. Increasing west winds will develop from south to north late afternoon with gusts 25-35 mph developing, especially south of the Mass pike. && .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 Sun into mid week. 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 /12Z 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/... Today...Moderate confidence. Mainly IFR/LIFR across the region through the morning, with gradual lifting of CIGS this afternoon to MVFR. Areas of rain through the day with localized heavier downpours, which will become focused west of the CT valley by late in the day. Low prob of an isold t-storm. Increasing W winds mid/late afternoon with gusts 25-35 kt developing, especially south of the Mass Pike. Tonight...High confidence. MVFR cigs improving to VFR. Sct showers continuing, but becoming less widespread, mainly western New Eng and focused over higher terrain. West 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. 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 SHORT TERM...KJC 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.