Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
237 FXUS61 KBOX 191832 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 232 PM EDT Sat Aug 19 2017 .SYNOPSIS... A cold front will slowly cross the region today, shifting offshore by evening. High pressure brings fair seasonable weather Monday and Tuesday. Another cold front sweeps through New England Wednesday, followed by more dry weather Thursday and Friday. && .NEAR TERM /UNTIL 7 PM THIS EVENING/...
-- Changed Discussion --
230 PM update... Interesting weather along the immediate eastern MA shoreline (from Cape Ann to Nantucket) with GOES-16 satellite imagery, surface observations and web cams confirming stratus and fog rolling back onshore as seabreeze circulation increases. The fog erodes as it moves westward and interacts with the warm land with temps a short distance from the coastline in the upper 80s. For example 69 at Boston/Logan airport and 88 at Norwood MA just to the southwest. Expecting low clouds and fog to play tag with the eastern MA coastline for the remainder of the day and then move offshore this evening as surface winds veer to the south and seabreeze circulation weakens. Otherwise a typical summer afternoon in progress with scattered diurnal clouds and temps well into the 80s. Surface boundary is located along and near the I95 corridor of RI and eastern MA with winds S-SE east of the boundary and providing humid conditions with dew pts in the U60s to L70s. Meanwhile to the west of the boundary across RI/CT and western-central MA dew pts drop off in the upper 50s to mid 60s courtesy of west winds. Mid level dry aloft providing a cap and precluding any TCU from developing into showers. However can/t rule out an isolated brief shower this afternoon along the boundary in eastern MA.
-- End Changed Discussion --
&& .SHORT TERM /7 PM THIS EVENING THROUGH 6 AM SUNDAY/... Cold front continues to move offshore and wash out, but drier air at the sfc will still lag well behind due to the inability to mix it out during the daylight hours. Meanwhile, low pres continues to wrap up in Quebec as fairly robust upper lvl shortwave rotates toward New England during the late evening hours, shifting E of the area by early AM Sun. This is accompanied by a secondary spike in K-indicies and PWATs through the column as it shunts the initial dry slot to the E, similar to comma-head style wrap-around. While forcing attendant to the wave is relatively strong, the remnant dry air should mitigate shower development, but the risk is non-zero. Some QPF on recent model runs, but given the initial drying, and the moisture spike mentioned above is quite modest, will maintain a generally dry forecast with this update and only suggest slightly more clouds than previous forecast. Day crew can reassess if POPs might be needed. With little change in low-lvl moisture, maintaining dwpts in the 60s, and increased cloud cover expected, overnight mins should once again only fall into the mid 60s at the coolest spots. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Big Picture... Subtropical high maintains sultry summer weather over the Southern USA. Zonal flow over the Northern USA and Canada early week amplifies during the mid and late week. Contour heights are normal to a little above normal early week, but fall below normal by late week. This supports warm summery weather early week, followed by cooler, drier air moving into New England late week. Model upper contour fields are similar through much of next week. Thermal fields and surface pressure fields show a similar distribution. This maintains confidence in the forecast data for our area. Details... Sunday through Tuesday... High pressure builds over the region during this period. Upper trough is directly overhead Sunday morning with lingering moisture below 800 mb but dry air above. Mid level air is at -10C or warmer, while the destabilizing part of the cold pool is near the Canadian border. Expect dry weather Sunday with some diurnal clouds but otherwise a fine day. Temps aloft at 13-14C should support max sfc temps in the low to mid 80s. Expect dry weather Sunday night to Tuesday, although increasing mid and high clouds during Tuesday. Light wind flow will allow sea breezes on Monday afternoon, but gradient on Tuesday suggests a general southwest flow. Mixing should reach between 800 mb and 850 mb each day. Temps of 14-16C Monday and 16-18C on Tuesday suggest max sfc temps in the 80s Monday and 85-90 Tuesday...cooler along the coast. Slow increase in humidity with dew points in the 60s. Winds in the mixed layer Tuesday suggest southwest gusts 15-20 knots. Tuesday night-Wednesday... Closed low digs over Quebec and the Northeast USA with shortwave driving a cold front into/through New England. Expect showers/scattered tstms with the front Tuesday night/Wednesday. Cold fropa Wednesday brings an end to the showers, but sufficient mixing to bring northwest gusts to 20 knots behind the cold front. Thursday-Friday... Surface high pressure builds over the region while upper trough moves overhead. Cold pool in the upper trough moves in with 500-mb temps forecast to reach -16C to -18C by Friday. Temps at 850 mb will be 8-10C. Moisture profiles show lots of dry air during that time but with a moist layer at 850 mb. Expect dry weather with potential for some diurnal clouds. Expect max temps in the 70s, possibly near 80 in spots. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... 1830Z update... Thru sunset... VFR most locations. The exception will be along the immediate eastern MA coastline with MVFR/IFR conditions in low clouds and fog. Isolated brief shower possible in eastern MA otherwise dry conditions prevail. After sunset... Onshore winds along the eastern MA coastline shift to S and then SW which will give way to improving conditions, likely VFR by 03z or so. Otherwise VFR prevails with just a low risk of brief MVFR in isolated shower overnight. Sunday and Sunday night... VFR, dry weather and modest west wind. KBOS Terminal...Moderate confidence. Low clouds and fog at 18z will play tag with the airport thru 00z or so. Thereafter winds shift from east to south and will promote improving conditions to VFR by 03z or so. KBDL Terminal...High confidence in TAF. Outlook /Monday through Wednesday/... Monday through Tuesday...High confidence. VFR. Areas of IFR in early morning fog/low clouds, then improving to VFR by each mid morning and continuing the remainder of each day. Tuesday night-Wednesday...Moderate confidence. VFR with areas of MVFR cigs/vsbys in showers and scattered thunderstorms. IFR cigs possible in early morning fog/low clouds especially in areas that have had some rain.
-- End Changed Discussion --
&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...Moderate confidence. Winds and seas will diminish this morning. Timing of current small craft advisories seems reasonable, although conditions may drop off more quickly than current advisories suggest. After advisories are dropped boating conditions should remain relatively quiet into the overnight hours, with the only issue being some localized marine fog which may restrict visibilities, especially on the S waters. Outlook /Sunday through Wednesday/... Sunday through Tuesday...High confidence. High pressure builds over the waters. Winds remain 15 knots or less, and seas 3 feet or less. Winds pick up a little on Tuesday, but remain 20 knots or less with seas 4 feet or less. Tuesday night-Wednesday...Moderate confidence. A cold front approaches from the Great Lakes, crossing the waters late Wednesday or Wednesday night. Southwest winds increase with gusts 20 to 25 knots during Wednesday. Winds shift from the northwest Wednesday night. Seas build Tuesday night and Wednesday reaching 5 to 6 foot heights on the outer waters. The southwest flow may also nudge those higher seas into RI Sound as well. A Small Craft Advisory may be needed on some of the waters during this time. && .CLIMATE... Highest recorded dew points on August 18 in any year PVD 76 in 2002 BDL 82 in 2002 BOS 77 in 1994 ORH 75 in 1987 Highest dew points yesterday PVD 76 from about 1130 to midnight EDT BDL 76 from about 630 PM to midnight EDT BOS 74 from about 11 PM to 1 AM EDT ORH 72 from about 740 PM to 1220 AM EDT So the PVD value ties highest for August 18. Highest value at PVD for August is 80. Highest value at PVD for anytime is 81. && .BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ254. Small Craft Advisory until 8 PM EDT this evening for ANZ255- 256.
-- End Changed Discussion --
&& $$ SYNOPSIS...WTB/Doody NEAR TERM...WTB/Nocera/Doody SHORT TERM...Doody LONG TERM...WTB AVIATION...WTB/Nocera/Doody MARINE...WTB/Doody CLIMATE...

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.