Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 281130 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 730 AM EDT Fri Apr 28 2017 .SYNOPSIS... A mild start this morning with some more patchy dense fog will lead to a mix of showers and isolated thunderstorms. Warmer highs today will give way to another mild night. A cold front crosses the region Saturday night, bringing much cooler weather for Sunday, especially along the coast. Another cold front will likely bring a period of showers sometime Monday into Tuesday. Another storm may approach New England late Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Widespread fog blanketed southern New England again this morning, with areas of dense fog toward the south coast of MA and RI. Expecting visibility to improve fairly quickly this morning, especially after a round of showers moves offshore by 10 AM. Will permit the Dense Fog Advisory to expire at 8 AM, although patchy fog may linger a bit longer than that. Just enough elevated instability this morning, with max 2-6km lapse rates about 7-7.5 C/km. This instability should move offshore my mid morning. Kept a mention of isolated thunderstorms in the forecast early. Wind shear is very weak, so not expecting any severe thunderstorms. Minor tweaks to temperatures and winds this morning to reflect observed trends. Also tweaked rainfall chances. The greatest chance for measurable rainfall will be across southeast MA. Previous discussion... Forecast remains on track for this morning. Approaching frontal system has resulted in an a surge of moisture thanks to southerly winds. This has resulted in a advection fog developing and moving onshore. Went ahead and expanded the dense fog advisory into RI as webcams show vsbys dropping from fog. Also expanded the timing, to get through the morning commute. Aside from the patchy dense fog, we continue to watch showers out west from approaching cold front. These showers are quite fragment due to the dry air aloft from weak mid-level ridge. However as they continue to move eastward, feel they will tap more into the low level moisture resulting in better coverage over the next few hours. Have noticed a few stronger showers with embedded thunder off the coast of NJ and south of Long Island. Latest SPC meso analysis shows some elevated instability across the area as well as steepening mid- level lapse rates. This well help support any thunder chances across the area this morning. Therefore will continue the mention of thunder. Showers and embedded thunder will move from west to east early this morning and should be offshore by the early afternoon hours. This afternoon... The front will swing through and stall/washout across the south coast by the afternoon. Anticipate clearing and the return of sunshine for today. Despite being behind the front, anticipate a mild day with highs in the in the upper 70s with cooler conditions along the south coast. Model guidance is hinting at some surface CAPE, good shear and steep lapse rates during the afternoon hours. However, subsidence behind the morning shortwave and very dry mid levels of the atmosphere should prevent convection from developing. As prev forecaster noted, still have the front lingering near by, so if there is any moisture we cant rule out the potential for an iso thunder. Something to keep an eye on later today. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Dry air aloft as mid-level ridge moves over the region. Continuous southerly flow however will limit overnight temps from cooling. In fact, anticipate another mild night as today`s frontal system is draped across the south coast. Dewpoints will also be on the rise, so cannot rule out another round of patchy fog, with the south coast begin the best spot for this to occur. For the second half of the night, moisture aloft will begin to increase in the mid-levels as an upper level shortwave and associated system approaches from the west. Guidance has speed up the timing, bringing showers through the area by dawn on Saturday morning. Am concern that the NAM appears to indicate a weaken MCS with the Hi-res guidance also showing a few stronger showers. This is plausible as guidance continues to indicated elevated instability overnight and the stalled front could be the focus for come convection as the wave pushes through. An area of high pressure to the north will slowly extend eastward during the later half of the day. This will push a low level boundary across the region during the afternoon. Will keep a low chance of showers and possibly a thunderstorm Saturday afternoon with some lingering instability, if the atmosphere can recover from morning convection. Temperatures on Saturday will be mild with highs in the mid to upper 70s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Overview... 28/00Z guidance is in reasonable agreement with the overall evolution of the synoptic pattern through Wednesday. Details become more problematic during the second half of next week. Monitoring two primary periods of precipitation: one early next week, and the other later next week. Will continue to favor a consensus blend to smooth over the less predictable details. Details... Saturday night through Sunday... High pressure noses into our region from southeast Canada. This will push a cont front to our south, and bring drier weather with near normal temperatures. Sunday night... A warm front start to approach our region. Scattered showers are possible north of this front. Monday-Tuesday... This is one of the more likely periods for precipitation. A low pressure moves through the Great Lakes, driving a warm front through southern New England. Some showers, and perhaps a few thunderstorms, are expected. A strong southwest low level jet should maximize moisture transport Monday night, resulting in periods of moderate to briefly heavy rainfall. Still need to refine the timing details. Wednesday-Thursday... This is probably going to be mainly a lull between two larger systems. Once the Monday/Tuesday system departs, looking at only a couple of weakening boundaries to contend with. A shortwave aloft may provide just enough lift to generate some showers into Thursday morning. After that time, expecting an increasing risk for showers ahead of another approaching low Thursday evening and night. This timing remains low confidence, and will need to be monitored for later forecast changes. && .AVIATION /11Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/... This morning...High confidence in trends. Moderate confidence in timing. IFR/LIFR in fog and drizzle early this morning. Passing cold front will push showers and embedded -TSRA from west to east by the late morning. After 18z...High confidence. Rapid improvement across the region to VFR. Winds turn W, with gusts to 15 kt at times. Tonight and Saturday...Moderate confidence. Mainly VFR conditions with chances of MVFR/IFR in patchy fog and stratus. Could see conditions lower in passing showers/thunder early Saturday morning. Conditions improve by the afternoon with a low risk for -TSRA. KBOS TAF...Moderate confidence in TAF. SW winds are marginal enough where there is a low risk seabreeze redevelops later this afternoon. The trigger for that will be rapid clearing and rising temperatures. KBDL TAF...High confidence in TAF. Outlook /Saturday Night through Tuesday/...Moderate confidence. Saturday night and Sunday...High confidence. VFR. Sunday night to Tuesday...Moderate confidence. MVFR/IFR cigs/vsbys in low clouds/drizzle and light showers Sunday night. VFR and areas of MVFR in showers Monday and Tuesday. Possible low level wind shear especially over RI and SE Mass Monday night and Tuesday morning. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...High confidence. Small Craft Advisories will remain in effect mainly over the offshore waters into tonight as a lingering 5-7 ft swell remains. Winds shifting to the west during the day will back to the SW by tonight and should remain below the 25 kt threshold through the period. The risk for a few thunderstorm offshore this morning continues with another risk tomorrow morning. Small Craft Advisories may be expanded into Saturday, but has low confidence on wave forecast at this time. Could also see 25 kt gusts across the near shore waters. Outlook /Saturday Night through Tuesday/...Moderate confidence. Winds expected to remain less than 20 kt through Monday. Southwest winds increasing ahead of a cold front Tuesday may result in gusts up to 30 kt Monday night into Tuesday, mainly across the southern coastal waters. Seas should remain less than 5 ft into Monday morning, then build across the outer coastal waters due to the increasing southwest flow Monday afternoon into Tuesday. && .TIDES/COASTAL FLOODING... * Isolated minor coastal flooding impacts during astronomically high tide tonight along the east coast The astronomical high tides remain very elevated into this weekend. Given a lingering swell offshore and its remnant surge, with high tide values only a few tenths shy of typical minor flooding levels, a Coastal Flood Statement continues for the high tide near 2 AM tonight for east coastal locations. At this time, we anticipate only minimal impacts at typically prone locations. Also, due to the breadth of the fetch, we may encounter enough wave action with lengthening periods on top of an elevated tide to cause pockets of erosion tonight along the Martha`s Vineyard south coast, Nantucket south and east coasts, and the outer Cape ocean side from Truro to Chatham. Boston High Tides (flood stage at Boston 12.5 feet)... 12.14 feet / Saturday 12:56 am && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 8 AM EDT this morning for MAZ020>024. RI...Dense Fog Advisory until 8 AM EDT this morning for RIZ002- 004>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ235- 237. Small Craft Advisory until 11 PM EDT this evening for ANZ250. Small Craft Advisory until 2 AM EDT Saturday for ANZ254>256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten MARINE...Belk/Dunten TIDES/COASTAL FLOODING...

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