Area Forecast Discussion
Issued by NWS Boston, MA

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273 FXUS61 KBOX 160201 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1001 PM EDT Fri Jun 15 2018 .SYNOPSIS... Dry weather continues this weekend with a warming trend each day. Dangerous heat and humidity is expected Monday along with record high temperatures. As a result, heat headlines will likely be needed. A warm front may trigger scattered showers and thunderstorms Sunday night. A second round of scattered showers and a few thunderstorms are possible late Monday into Tuesday with a passing cold front. Seasonable temperatures and lower humidity return by mid to late next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 10pm update... Leftover mid clouds continue to push offshore as subsidence inversion builds in from the NW. However, will monitor for continued low stratus/fog development near the S coast thanks to developing inversions where sunshine was observed the latest. In this same inversion, weak onshore flow will increase the moistening thanks to marine influence. At the time of this writing, WST has gone to half mile in fog and stratus. This layer is thin however, and GOES16 shows this. Will continue to monitor, but the primary change with this update will be to increase fog and low cloud potential, expanding toward the Cape and Islands as well as portions of the RI/MA Coastal plains. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Sat... Dry and clear conditions tomorrow as a high pressure builds into the region, keeping dew points in the 50s. The ECMWF suggests 18z and 00z 2M temps reaching into the low to mid 80s. It`s possible that some areas could reach into the upper 80s given weak winds and little cloud cover. Sat night... Winds become westerly-southwesterly as the high pressure pushes southeast away from New England. Given minimal cloud cover, low dewpoints, and light winds at the surface, we could see yet another night of radiational cooling across the interior, dropping lows into the 50s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Spotty showers & thunderstorms possible late Sunday into Sunday night * Dangerous heat and humidity Mon along with record high temps * Scattered showers and a few thunderstorms possible well inland late Mon into Mon night * Showers & t-storms linger through Tue with a slow moving cold front * Less humidity and close to seasonable temperatures Wed, then a bit warmer late next week Details... Sunday and Sunday night... Large high amplitude H5 ridge, with a 591 dm center across the TN valley into the interior SE states, dominates the eastern half of the U.S. early Sunday. The ridge will slowly shift to the eastern seaboard as the northern extend of the ridge starts to flatten later in the day. A warm front will shift NE in the W-SW flow aloft late Sun through most of Sun night, which could trigger a few showers and isolated t-storms. H85 temps rise to +16C to +18C Sun afternoon into evening. Expect temps to top off in mid-upper 80s with a few locations reaching the lower 90s away from the immediate coast. As the warm front moves through, will see dewpoints increase to the lower-mid 60s overnight. A few showers and storms may linger especially across the Route 2 area of N Mass. Monday and Monday night... Hot and increasing humid conditions move in across the region Monday as H85 temps surge up to +20C to +22C by midday. As the warm front shifts offshore and weakens, W-SW winds will be in place as another front slowly pushes S across northern New England by around midday or early afternoon. All models signal dangerous heat and humidity across the region away from the immediate coast during Monday, with dewpoints increasing to the lower 70s across the interior. Temps will increase to the mid- upper 90s, with the highest temps across the CT and Merrimack valleys. A couple of spots may even touch 100. The combination of the high temps and dewpts will likely produce dangerous heat indices, upwards to 100 to 104 degrees. Heat advisories will likely be needed. Also, record highs could also be tied or exceeded at a couple of spots. See the Climate section for the details. Excellent deep low and mid level mixing up to 8Kft or greater, so could see gusts up to around 25-30 mph especially along the S coast and on the near shore waters where the edge of a higher H925 and H95 jet just S of the region. The slowly moving cold front will push some instability into the region Mon afternoon and night, mainly near and N of the Mass Pike into the CT valley. With the nearly zonal steering flow aloft, will take a while for the front push through. Best lift and dynamics remain N of the region, so carried slight chance to chance POPs during this timeframe. Tuesday and Wednesday... Will continue to see the chance for showers and isolated t-storms Tue into Tue night. Model suite showing an increasing solution spread, so exact timing and track in question, though it should move off the S coast Tue night before stalling offshore. A few showers may linger along the S coast into early Wed morning, but should push offshore by around midday. Should see more seasonable temps with falling dewpoints, so it should be more comfortable on Wednesday. Highs both days will be in the lower-mid 80s away from the coast, with cooler temps along the coast. Thursday and Friday... Some question whether the stalled front to the south may try to make a run back N or weak waves may bring patchy showers along the S coast. At this point, looks like dry and warm conditions will be in place. Expect temps to run about 5 to 10 degrees above seasonal normals away from the S coast. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Tonight...High confidence for interior, low confidence for the Cape and Islands. VFR conditions across most locations, though MVFR CIGS linger along the immediate S coastal terminals. Conditions should improve to VFR by 01Z or so. Possible IFR conditions early tomorrow morning across the Cape and Islands due to fog, but will likely lift around 12Z. Saturday...High confidence. VFR across the region. Winds out of the W at or below 10 kt. Low risk for E coast sea breezes. Saturday night...High confidence. VFR. FEW-SCT clouds AOA 10Kft. KBOS Terminal...High confidence in TAF. VFR. Winds light E-SE becoming light SW this evening. KBDL Terminal...High confidence in TAF. Outlook /Sunday through Wednesday/... Sunday: VFR. Sunday Night: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA, slight chance TSRA. Monday: Mainly VFR, with areas MVFR possible. Windy with local gusts to 30 kt. Slight chance SHRA, isolated TSRA. Monday Night: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA, isolated TSRA. Tuesday: Mainly MVFR, with areas VFR possible. Chance SHRA, slight chance TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Wednesday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Tonight into Sunday: Light NW winds and diminishing seas. Slight risk for some fog development along the Cape and Islands early tomorrow morning, but should dissipate shortly after 12z. Saturday Night: WNW winds less than 25 kt. Outlook /Sunday through Wednesday/... Sunday: Winds less than 25 kt. Sunday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms. Local visibility 1 to 3 nm. Monday: Moderate risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms. Monday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms, patchy fog. Areas of visibility 1 to 3 nm. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms. Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Wednesday: Winds less than 25 kt. Slight chance of rain showers. && .TIDES/COASTAL FLOODING... Coastal Flood Advisory remains in effect for the early morning Sat high tide. High tides for early Sat morning remain astronomically high, running about 12.1 ft in Boston Harbor. With this past high tide cycle, an additional 0.8 ft was observed. Tonight, wave action offshore is lessened, but easterly flow is expected through the day. Therefore, we could see another round of very minor coastal flooding with the high tide Sat morning. && .CLIMATE... With increasing heat and humidity early next week, high temperatures may approach or exceed record levels on Monday. Here are the record highs for Monday June 18... Boston/BOS 94 degrees set in 1907 and 1929 Windsor Locks/BDL 95 degrees set in 1957 and 1994 Providence/PVD 94 degrees set in 1929 Worcester/ORH 93 degrees set in 1907 and 1929 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Coastal Flood Advisory until 4 AM EDT Saturday for MAZ007-015- 016-019-022-024. RI...None. MARINE...None. && $$ SYNOPSIS...EVT/Correia NEAR TERM...Doody SHORT TERM...Correia LONG TERM...EVT AVIATION...EVT/Correia MARINE...EVT/Correia TIDES/COASTAL FLOODING... CLIMATE...

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