Area Forecast Discussion
Issued by NWS Boston, MA

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114 FXUS61 KBOX 270809 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 409 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 backdoor cold front crosses the region Saturday night, bringing much cooler weather on 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/... 400 AM Update.... Overall trend in the forecast remains on track for this morning. Saturated low profiles has resulted in fog and drizzle for much of the region. Conditions are slowly improving across the Berks as stacked low begins to pull eastward. Anticipate this trend to continue this morning for the Pioneer Valley. The eastern half of the region will remain socked in and could linger into the morning commute. Dense fog advisory looks to be in on track. While some of the sites have improved, believe they could still drop below 1SM by morning. So will continue with the adv. Otherwise, a warm start for today as temps are still in the 50s. Today... 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 6 PM FRIDAY/... 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 /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Brief scattered showers and perhaps an isolated t-storm possible very late Thu night into mid morning Fri * Dry/very mild to warm temps expected by Friday afternoon * Warm on Sat away from the south coast with the low risk for a few afternoon/early evening t-storms * Turning much cooler Sat night and Sun especially on the coast * Period of showers likely sometime Mon into early Tue Details... Thursday night and Friday morning... Still a lot of lingering low level moisture trapped beneath the subsidence inversion based on model cross sections Thu night. Therefore, feel there will be an abundance of low clouds and fog patches with even some drizzle possible. The clouds and low level moisture should keep low temperatures mainly in the lower to middle 50s. The majority of Thu night will be dry, other than perhaps some drizzle. However, a fast moving shortwave approaches the region toward daybreak Friday with a burst of elevated instability. This will probably result in a brief band of scattered showers and perhaps a few embedded thunderstorms. Activity should be scattered and short-lived with it mainly coming to an end by mid to late Friday morning. Friday afternoon... Steep mid level lapse rates along with decent instability/shear develop by Friday afternoon as temps warm with dewpoints in the 50s. However, subsidence behind the morning shortwave and very dry mid levels of the atmosphere should result prevent convection from developing Friday afternoon. Therefore, expect dry weather and with plenty of sun Friday afternoon. Highs should recover in the 70s to near 80 away from the marine influence of the south coast. Friday night... Upper level ridge off the southeast coast will pump unseasonably mild air into southern New England. Low temps should only drop into the middle to upper 50s in most locations. May also see some patchy fog develop given relatively high dewpoints in place. Saturday... A rather warm day appears to be in the cards away from the south coast, Cape and Islands. Given west to southwest flow out ahead of an approaching pre-frontal trough/cold front, should see high temps reach 80 to 85 in many locations. At the same time, a pre-frontal trough will be dropping south into the region but it is uncertain if it will trigger a few thunderstorms during the afternoon. While there are impressive wind fields along with some instability, forcing will be limited. The models actually show subtle height field rises during the afternoon, which is not normally a good sign for convection. Much of the guidance also pushes the plume of steeper mid level lapse rates south of the region by Saturday afternoon. Nonetheless, "If" a few thunderstorms are able to develop the risk for an isolated strong to severe t-storm or two would exist given impressive wind fields. Currently, we will consider this a low risk given limiting factors stated above, but certainly something will have to watch with pre-frontal trough. Saturday night and Sunday... Despite upper level ridging, a strong high pressure system will build into eastern Canada. This will send a backdoor cold front south of the region Sat night and result in much cooler temps on Sun. Highs Sunday will probably only in the 50s along the coast with 60s further inland. May see a spot shower or two Sat night/Sun, but the vast majority of the time will feature dry weather given lack of forcing. Monday into Tuesday morning... Low pressure across the central Plains will lift northeast across the Great Lakes Monday and then into eastern Canada Tue. Some over running showers are possible early Monday, but a period of steadier showers with even brief heavy rainfall will be possible later Mon into early Tue with the cold front. Temps highly uncertain on Mon as a frontal boundary may be jammed up across the region. Overall, coolest temps probably in northeast MA and mildest in our CT zones. 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 /08Z 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/... Before 12z...Moderate confidence. Mainly IFR to LIFR conditions with the most widespread/lowest conditions across the eastern MA coast, Cape and Islands. This a result of dense fog, drizzle and scattered showers. 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 /Friday Night through Monday/... Late Friday morning and afternoon. Moderate to high confidence in mainly VFR conditions. Saturday and Sunday...Moderate confidence in mainly VFR conditions. Monday...Moderate confidence. MVFR/IFR conditions possible in lower clouds and some showers, particularly late Mon/Mon night. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...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 /Friday Night through Monday/... Saturday and Sunday...Moderate to high confidence. Winds and seas mainly below small craft thresholds, but some marginal small craft seas for a time on Saturday across our southern waters. May also see some near shore southwest wind gusts of 20 to 25 knots Sat afternoon. Monday...Moderate confidence. Winds and seas will probably increase to small craft thresholds on gusty southerly winds late Mon and especially Mon night ahead of the next cold front. && .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...Dense Fog Advisory until 9 AM EDT this morning for CTZ004. MA...Dense Fog Advisory until 9 AM EDT this morning for MAZ005>007- 012>024. RI...Dense Fog Advisory until 9 AM EDT this morning for RIZ001>008. MARINE...Small Craft Advisory until 2 PM EDT Friday for ANZ235-237. Small Craft Advisory until 8 PM EDT Friday for ANZ250-254>256. Small Craft Advisory until 9 AM EDT this morning for ANZ251. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten MARINE...Belk/Dunten TIDES/COASTAL FLOODING...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.