Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 281735 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 135 PM 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/... 10AM update... Area of convection continues to move across the Islands this morning along the nose of an LLJ within an area of slightly higher elevated instability. Both the LLJ and the unstable airmass will continue to shift E through late morning. Otherwise, already noticing clearing in the SC across interior SNE which, given the timing should still allow for plenty of warming as the downsloping W flow develops. Still looking at highs in the mid 70s to low 80s, coolest along the S coast thanks to a slight onshore component to the flow. Not as concerned about afternoon convection in spite of the front slowing to a stall across S portions of the forecast area, mainly due to drier air entraining through the column and capping the airmass. However, will need to watch for continued cloud cover along the S coast S of the front, as it may struggle to erode through the afternoon. 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 /17Z FRIDAY THROUGH TUESDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short term...through Saturday night. Through 04Z (midnight local)...Moderate confidence. VFR now through this evening for all TAF sites except ACK, which may linger in the low CIGS for a bit longer but transitioning to a risk for some MVFR/IFR CIGS with SHRA/TSRA (see below). Terminals from WST east the Cape/Islands may once again see a period of late evening low CIGS and LIFR conditions, most likely on ACK/MVY. Southerly sea breezes likely this afternoon, lower risk for E coast. After 04Z through tomorrow...Moderate confidence. Still have to watch LIFR/IFR conditions mainly coastal RI and S coastal MA in low CIGS/fog. Otherwise VFR mainly inland but with a risk for some SHRA/TSRA. Best chance for these would be across CT/RI/SE MA between 09Z and 14Z from W-E. Lower risk further N. After these move through expect SCT-BKN low end VFR clouds through the day. Winds shift from SW to W in the morning with a few gusts around 20 kt during the afternoon. Tomorrow night...High confidence. W flow and mainly VFR. KBOS TAF...Generally high confidence in TAF. If sea breeze occurs this afternoon/evening it would be relatively short lived. 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.
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&& .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...None. RI...None. 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...Doody/Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Doody MARINE...Belk/Dunten TIDES/COASTAL FLOODING...

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