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. --
938 FXUS61 KBOX 170709 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 309 AM EDT Thu Aug 17 2017 .SYNOPSIS...
-- Changed Discussion --
Dry and pleasant conditions continue into tomorrow. A weather system moving through the Great Lakes Region towards the end of the workweek will bring showers and scattered thunderstorms to southern New England during Friday and Saturday. High pressure returns with fair seasonable weather Sunday through Tuesday. A cold front approaches from the west Tuesday night and Wednesday, bringing our next chance of showers.
-- End Changed Discussion --
&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 200 AM Update... Forecast remains on track for the overnight hours. Weak wave moving through the northwest flow this morning has trigger some strato cu per latest IR imagery. Dewpoints continue to drop with a few locations across northeast MA in the 40s. Surface temps are radiating out with some locations in the low to mid 60s. Metro regions are hanging tough with temps in the 70s, but with the cooler dewpoints anticipate them to drop over the next few hours. OVerall a very pleasant night across southern New England. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
Thursday... High pres crests over the region providing stout subsidence. Despite the mostly sunny conditions this suggests, the combination of suppressed mixing and a cooler start to the day will lead to overall high temps a few degrees cooler than yesterday. This is also in spite of generally W flow. Mainly upper 70s and low 80s in the warmest spots where the downsloping can be maximized. Overall a pleasant day especially with dwpts remaining in the 50s. Will still need to watch mainly exposed beaches across Cape Cod and Nantucket, as the remnants of Gert continue to shift east, a lingering swell could maintain a moderate risk for rip currents through the day in these areas. Thursday night... A pleasant evening to start, however upper lvl wave will be tilting and lifting through Ontario and Quebec with sfc wave pushing a warm front toward New England. PWATs increase through the overnight hours, such that by 12Z Fri, they near 2.00 inches (or nearly 2 std deviations above normal). Initial overruning is weak and this moisture load is from the top of the column to the sfc. Therefore, expecting only building clouds through the evening, with the risk for any precipitation holding off until the early morning hours. Indeed, timing of measurable QPF has slowed on regional models due to this initial lack of lift and dry column. Still could see some wetting rainfall by sunrise mainly W of the Worcester hills in MA and Thames river region of CT. Noting some QPF bullseyes, but these are mostly likely some convective feedback. Column remains relatively stable through 12Z. The increased moisture from W-E will limit diurnal cooling in spite of the weak pres gradient to start. Coolest areas will likely be across E MA/RI, where some radiational cooling can occur initially. Overnight mins range from the upper 50s in these cooler spots to the low 60s elsewhere due to the increased cloud cover.
-- End Changed Discussion --
&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Big Picture... Subtropical high remains in control across the Southern USA while a general zonal flow continues across Canada and the Northern USA. The high actually builds over the Western USA early next week, supporting a deepening of the wave pattern during next week. One shortwave moves through New England over the weekend. A second shortwave moves across from the Gulf of Alaska, forms a closed low over northern Canada, and then digs over Quebec midweek. Contour heights are normal to a little higher than normal through early next week. As the Quebec closed low deepens, heights over New England dip below normal midweek next. Model mass and thermal fields from the 00Z suite are in general agreement through Wednesday, building forecast confidence. Details... Saturday... Moderate confidence. Models hold the the cold front over western and central sections of Southern New England while moisture fields race east and drier air moves in during the afternoon. PW fields show 1.5 inch values move east of BOS-PVD by Saturday afternoon. CAPE fields show 1000-1500 J/Kg east of a ASH-ORH-IJD line in the afternoon. Winds aloft are marginally significant, with 25-30 knots at 850 mb and 35-40 knots at 500 mb. Stability parameters are mixed, with Totals in the mid 40s, except upper 40s ECMWF, and LI values subzero. Expect the main area of showers/heavy downpours to move east of Massachusetts during the morning, but with lingering scatterd showers/thunder possible in the afternoon until the cold front moves past. With the flow becoming more southwest, expect deeper mixing than on Friday...and so a warmer airmass. Temps of 15-17C at 850 mb would support mid-upper 80s. Depending on the degree of clearing, temps could be a little lower than this. Expect max temps in the 80s. Surface dew points in the southerly flow will linger in the upper 60s and low 70s, so expect a warm and very humid day. Saturday night... Cold front moves offshore, and surface winds become northwest. Expect any showers to taper off. Skies will either clear or partially clear overnight. Dew points will linger in the 60s, with min temps close to that level. Sunday... Upper shortwave and the coldest of the cold mid-level temps will be over New England. The more significant cold temps as well as cloud- level moisture will be over NH-VT. Cross-sections show Southern New England will have a moist layer based at 850 mb, with drier air closer to the surface. Expect diurnal clouds, probably a bit more than guidance is suggesting, but otherwise a fair day with less noticeable humidity. Surface high pressure builds in with light variable wind Sunday night. With dew points in the upper 50s and around 60, expect min temps around this same range. Guidance temps were nudged a couple of degrees colder. Monday-Tuesday... High pressure builds over the region Monday and shifts offshore south and east by Tuesday. Cross sections show dry air in place at most levels through Tuesday evening, so expect dry weather both days. Increasing mid and high clouds Tuesday ahead of the next weather system. Temps aloft 14-15C Monday and 15-17C Tuesday, supporting low-mid 80s Monday and mid to upper 80s Tuesday. Tuesday night-Wednesday... Closed low digs over Quebec and the Northeast USA with shortwave driving a cold front into/through New England. Expect showers/scatterd tstms with the front Tuesday night/Wednesday.
-- End Changed Discussion --
&& .AVIATION /07Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... Before 00z...High confidence. VFR except some very patchy ground fog early AM mainly at typically prone terminals. Today...High confidence. VFR. Winds shift lightly W during the day except sea breezes along coast. Tonight and tomorrow...Moderate confidence in trends, lower confidence on timing. VFR to start with deteriorating conditions after 09z as widespread rain approaches. Conditions will fall to MVFR/IFR through the day as rain moves from west to east and could be heavy at times restricting vsbys. Iso -TSRA is also possible on Friday. Southerly winds with gusts near 15 kts by the afternoon. KBOS Terminal...High confidence in TAF. Sea breeze development expected for Thu. KBDL Terminal...High confidence in TAF. Outlook /Saturday through Monday/... Saturday... Moderate confidence. MVFR/IFR cigs and vsbys in showers and fog Saturday morning will improve to predominant VFR during the day. Continued MVFR ub scattered showers/thunder through afternoon especially in RI/Eastern Mass. Southerly winds during the day will shift from the west/northwest Saturday night after a cold front moves through. Areas of IFR cigs/vsbys in fog and low clouds later Saturday night. Sunday and Monday...Moderate-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.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
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. Noting seas have reached 8-9 ft along the open ocean waters S of S New England as hurricane Gert begins its E shift. This will allow these seas to gradually recede through the overnight hours. Small craft advisories continue, but will be able to be dropped as the night progresses. Otherwise, mainly quiet boating weather continued into tomorrow night after these seas recede. Outlook /Saturday through Monday/... Saturday...Moderate confidence. Lingering potential for scattered showers/tstms through the day, diminishing west to east Saturday night. Diminishing wind through the day. Some gusts 20-25 knots in the morning. Seas near 5 feet on the outer waters and on RI Sound, but trending lower later in the day. Sunday and Monday...Moderate-High confidence. High pressure builds over the waters. Winds remain 20 knots or less, and seas 4 feet or less. Leftover showers early, but these move off to the east during the morning.
-- End Changed Discussion --
&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 8 AM EDT this morning for ANZ254-255. && $$ SYNOPSIS...WTB/Doody NEAR TERM...Dunten SHORT TERM...Doody LONG TERM...WTB AVIATION...WTB/Dunten MARINE...WTB/Doody

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