Area Forecast Discussion
Issued by NWS Boston, MA

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540 FXUS61 KBOX 271407 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1007 AM EDT Thu Apr 27 2017 .SYNOPSIS... Fog and drizzle will linger across the east coast today and into tonight. A fast-moving disturbance may bring a few more rain showers and perhaps an isolated thunderstorm very late Thursday night into mid morning Friday, with a drying trend Friday afternoon. Mainly dry and warm weather for Saturday afternoon. 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 early Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 am update... Minor adjustments this morning. Noting a few breaks in W MA/CT thanks to infusion of drier air into the column under a more W component to the flow. This should lead to enough breaks to realize some of the upper lvl warm air where H85 temps continue to hover above 10C. Meanwhile E areas remain under influence of trapped moisture much of the day. Therefore, could be a lot of parity in temps across the region especially this afternoon. Latest guidance (even mesoscale guidance) is likely a bit too warm for E coast. Tried to adjust based on current trends to better reflect expected temperature outcomes. Previous Discussion... Fog burns off in the morning with daytime heating and as more westerly flow develops in the atmosphere. The upper level low moves farther east of the region as the surface low dissipates. Still have light easterly flow, so fog and drizzle may persist a bit longer across the immediate east coast but should push offshore by the late morning/early afternoon. More of a return W-SW flow develops in the region thereafter helping increase temperatures. Models agree on a substantially warmer day today, getting well into the 60s for a majority of the region with a few sites reaching 70s. This is cooler than some of the guidance as low stratus will limit heating today. However, if clouds break up more than current thinking then many spots could reach 70 and current forecast will be to low. Still anticipate cooler conditions along the eastern coastline. Overall expect a dry weather day as a shortwave ridge will move across the area on Thursday. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... Tonight and Friday... The next low pressure system and associated upper level trough will be approaching late tonight into Friday morning. The low pressure will be well west of the area and passing across the upper Great Lakes and into western and central Ontario. Meanwhile, the surface cold front will be approaching southern New England and running into the upper level ridge, which will be causing it to weaken. There will initially be enough vertical lift overnight into early Friday along with some elevated instability to give the region some showers and thunderstorms. Outside of the rain with the flow ahead of the cold front turning more southerly, the region will see a return of at least patchy fog tonight into early Friday with more onshore flow and inherent moisture advection. The front should be through by the afternoon, allowing for clearing and the return of sunshine. Despite being behind the front, anticipate a mild day on Friday afternoon with highs in the low to upper 70s with cooler conditions along the south coast. Model guidance is hinting at some surface CAPE,good shear and steep lapse rates Friday afternoon. However, subsidence behind the morning shortwave and very dry mid levels of the atmosphere should result prevent convection from developing Friday afternoon. Something to keep an eye. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Highlights... * Warm on Sat away from the south coast, with a low risk for a few afternoon/early evening thunderstorms * Turning much cooler Sat night and Sun, especially on the coast * Period of showers likely sometime Mon into early Tue Details... Friday night... Mid level dry air moves off to our east late at night. An approaching front to our west should be enough to start moisture pooling once more, late. Dry weather should prevail. Given the higher starting point from earlier Friday, expecting min temperatures to be near the normal high temperatures. Saturday... With a slow-moving front to our west should mean one more day of well above normal temperatures. As this front gets closer to southern New England, and temperatures get higher, there will be an increasing risk for showers and a few thunderstorms. The critical factor for any thunderstorms will be how quickly the mid level dry air exits. Mid level lapse rates are marginal, and should be most favorable to our south. Will need to monitor this over the next day or so, but still thinking thunderstorms remain a rather low risk. Saturday night and Sunday... A strong high pressure system will build into eastern Canada. This will send a cold front south of the region Saturday night, resulting in much lower temperatures Sunday, but still near normal. May see a spot shower or two Saturday night/Sunday, but the vast majority of the time should remain dry. Monday into Tuesday morning... A low pressure still expected to move across the Great Lakes Monday, then into eastern Canada Tuesday. Timing of the warm front is still in question, and will likely waver over the next few days. Leaning toward the slower end of the solution envelope, with a strong high pressure over Labrador. Tricky temperatures Monday. If this warm front gets hung up to our south, the current forecast is likely a little too high. Tuesday afternoon into Wednesday... Low confidence given the time range, but most guidance suggests mainly dry and pleasant weather as a weak ridge of high pressure builds in from the west. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... Today...Moderate confidence. Conditions improve to MVFR across the interior. Meanwhile along the coast, LIFR conditions should improve by late in the morning/afternoon but probably only to IFR thresholds given moist onshore flow. Tonight...Moderate confidence. Conditions will sock back in again tonight with mostly IFR conditions across the eastern half of the region. MVFR out west. Low confidence on LIFR conditions. Friday...High confidence. Improve conditions by the afternoon as showers with isolated thunder moves from west to east during the morning hours. KBOS TAF...Moderate confidence in TAF this morning, high confidence this afternoon. KBDL TAF...High confidence in TAF. Outlook /Saturday through Monday/... Saturday and Sunday...High confidence in mainly VFR conditions. Monday...Moderate confidence. MVFR/IFR conditions possible in lower clouds and some showers, especially late. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. Small Craft Advisories are in effect for the southern and ocean waters. Seas will remain above 5 feet due to lingering swell from low pressure system south and east of the region. Vsbys restrictions across the waters will continue today and into tonight in dense fog. Approaching cold front will be weak as it crosses the waters on Friday. However it will help improve vsbys on Friday. Still will see lingering 5 footers across the outer waters so SCA has been extended. Outlook /Saturday through Monday/...Moderate confidence. Winds expected to remain less than 25 kt through most of this period. Rough seas should slowly diminish across the outer coastal waters Saturday night into Sunday. There may be a few nearshore gusts to 25 kt Sunday. Will need to monitor Sunday for a possible Small Craft Advisory as a cold front passes by. && .TIDES/COASTAL FLOODING... * Isolated minor coastal flooding impacts during astronomically high tide tonight along the east coasts We are in a spring tide cycle with high tides that are astronomically high. This combined with an anticipated storm surge of around 0.5 to 1 foot may set the stage for isolated pockets of minor coastal flooding along the east coasts around the time of high tide very late tonight. The astronomical high tides remain very elevated through the end of the week. 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)... 12.15 feet / Friday 12:15 am Providence High Tides (flood stage at Providence 7 feet)... 6.25 feet / Thursday 9:50 pm && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT Friday for ANZ235-237. Small Craft Advisory until 8 PM EDT Friday for ANZ250-254>256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Doody/Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten MARINE...Belk/Dunten TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.