Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 121735 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 135 PM EDT Thu Oct 12 2017 .SYNOPSIS... Strong high pressure over Quebec this morning builds southward into New England today through Friday, providing a drying trend and seasonably cool weather. Warmer and more humid conditions arrive over the weekend as the high moves offshore and a cold front approaches from the west. This setup will also result in scattered showers at times especially Sunday night. The front moves offshore sometime Monday followed by drier, less humid and seasonably cooler weather early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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130 PM update... For most of the area, sunny/mostly sunny skies expected through the remainder of this afternoon, as high pressure centered over southern Quebec builds into New England. Gusty NE winds will begin to diminish this afternoon as the pressure gradient over our area relaxes. The exception to the abundant sunshine, for at least a few hours, is across the South Shore in MA, and the Cape and Islands. The onshore flow has enabled a swath of ocean effect clouds. As the high pressure continues to build south and the subsidence inversion lowers, this cloud cover should begin to erode. Thinking this would occur around or somewhat after sunset. Afternoon high temps will be lower than they have been over the last few days, but close to seasonal normals for mid October. Expect temps to peak out mainly in the lower-mid 60s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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Tonight... Skies should become mostly clear early this evening across the South Shore and Cape/Islands as the high pressure continues to build southward. Otherwise, mainly clear skies are expected tonight, with winds becoming light or calm winds thanks to large high pressure passing overhead. Will see excellent radiational cooling. Temps will drop back to the 30s away from the coast, with the potential for frost to develop in the normally prone locations across interior E Mass, N CT and across the CT valley. Have issued a Frost Advisory for most of Mass and N CT for late tonight into early Fri morning, with temps potentially falling close to freezing. Temps will bottom out in the lower-mid 30s across most inland areas, ranging to the 40s along the immediate coast and urban centers. Friday... Expect leftover chilly temps through 13Z, then should recover nicely. Temps will top off close to or a few degrees below seasonal normals. Some mid and high clouds will push in from S-N during the day, but skies should average out mostly sunny. Winds shift to S-SE as they diminish. Some short range models signaling some low level moisture may try to work into far western areas late in the day, but expect a dry day. Highs will range from 60-65 at most locations, though could be a bit cooler across the higher inland terrain.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Warmer and more humid this weekend * Risk of scattered showers this weekend, mainly Sunday night * Trend toward drier, less humid and cooler weather early next week Friday night... Tranquil weather especially during the evening hours with surface ridge across the area. Dry airmass still over the region with dew pts in the upper 40s and low 50s. This combined with light winds will promote temps to fall quickly with sunset. However return flow/ WAA pattern develops later at night with clouds overspreading the region. Thus temps should level off second half of the night. Fairly large spread among the models regarding strength of low level jet and accompanying moisture/instability burst as warm sector approaches. NAM and GEFS more robust and support shower/rain threat late Fri night from south to north in response to large jump in PWATs and K indices. Meanwhile remainder of guidance not as impressive and hold off any precip until sometime Sat. Given the uncertainty will follow a model blend which offers slight chance pops Fri night increasing to chance toward daybreak Sat. Saturday... NAM and GFS both have lots of clouds across the area as the warm sector overspreads the region. BUFKIT time sections show this moisture below 700 mb. However forcing for ascent is weak and instability is limited (SB and aloft). Thus any shower activity should be isolated/widely scattered. So chance pops from a model blend seem reasonable. A washout is not expected with many hours of dry weather anticipated. Model consensus is for 925 mb temps rising to +14C/+15C. Given lots of clouds are expected full sun temps will likely not be realized. Nonetheless highs should still manage to climb into the low 70s given low level WAA. It will be humid as well with dew pts rising into the low and mid 60s. Sunday... Core of warm sector overspreads the area with 925 mb temps rising to +16C to +17C along with dew pts climbing into the mid 60s, impressive for mid to late Oct. Still lots of clouds around in the warm sector but given magnitude of low level WAA highs of 75-80 seem plausible. For what it`s worth the EC ensembles show low prob of 80+ Sun afternoon across interior SNE. By late Sunday and especially Sunday night short wave trough and attending cold front approach the region from the west. Both EC and GFS show good moisture pooling ahead of the front Sunday evening and overnight with K indices rising into the 30s and PWATs +2 standard deviations above climo. This combined with modest synoptic and frontal scale forcing should result in a period of scattered showers late Sunday into Sunday night from west to east. However short wave trough is deamplifying with time as it climbs over the eastern seaboard ridge, resulting in weakening forcing for ascent. This combined with limited instability aloft and at the surface will likely result in showers diminishing in areal coverage from west to east. Thus higher pops west, lowering east. Other issue Sunday will be increasing southwest winds as low level jet develops over the area. GFS bufkit soundings indicate gusts up to 40 kt possible given warm sector airmass over the area providing steep low level lapse rates. Given trees remain fully leaved there is a low risk if wind speeds approach or exceed 40-45 mph some minor wind/tree damage is possible. Early Next Week... Cold front moves offshore early Mon with drier, less humid and cooler air overspreading the region. Coolest air arrives Mon ngt into Tue behind trailing short wave trough and attending secondary cold front. Both GEFS and ECENS ensembles lower 850 temps down to 0C over southern New England 12z Tue. However temps moderate by middle of next week. Thus brief touch of fall weather Mon night into Tue. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. 1730Z update... Today...VFR, except for some marginal MVFR-VFR cigs this afternoon across the Cape and Islands. Gusty NE winds this afternoon will relax some later in the day. Tonight...Mainly VFR, though some marginal MVFR/VFR cigs may linger over the Cape/Islands thru 01-03Z. Winds gradually diminish this evening. May see local patchy late night fog with brief IFR-LIFR conditions in some of the locally prone inland areas. Friday... VFR continuing, with clouds increasing during the day. KBOS TAF...High confidence. VFR with mainly clear skies this afternoon. ENE wind gusts up to 20 kt possible through early afternoon, then diminishing. Clear skies and E winds around 10 kts tonight. KBDL TAF...High confidence. VFR. May see brief patchy fog after 06Z with local MVFR VSBYS possible. Outlook /Friday Night through Monday/... Mainly MVFR-VFR with scattered showers, especially Sunday night. Southwest winds become gusty Sunday with speeds up to 35-40 kt possible. Cold frontal passage sometime early Mon with dry weather thereafter along with diminishing winds and VFR conditions.
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&& .MARINE...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Expect NE winds gusting up to around 25-30 kt, highest across the southern outer waters today, then will become E-NE and diminish tonight. Seas up to 5-7 ft, highest on the southern outer waters into this evening, then slowly subside especially on the eastern waters later tonight but remain at or above 5 ft on the southern waters. Small crafts continue for all waters. Outlook /Friday Night through Monday/...Moderate confidence. High pressure Fri night moves offshore Sat with winds becoming SW then. Vsby may lower in patchy fog, spotty showers Fri night thru Sun with showers most numerous Sunday night. SW winds increase to 20- 30 kt Sunday with gusts up to 40 kt possible. Cold frontal passage early Mon followed by diminishing winds, dry weather and good vsby.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Frost Advisory from 3 AM to 8 AM EDT Friday for CTZ002>004. MA...Frost Advisory from 3 AM to 8 AM EDT Friday for MAZ002>006- 008>014-017-018-026. RI...None. MARINE...Small Craft Advisory until 4 AM EDT Friday for ANZ232. Small Craft Advisory until 6 PM EDT this evening for ANZ233- 234-251. Small Craft Advisory until 4 PM EDT this afternoon for ANZ231. Small Craft Advisory until 3 PM EDT this afternoon for ANZ236. Small Craft Advisory until 6 AM EDT Friday for ANZ235-237. Small Craft Advisory until 8 PM EDT this evening for ANZ250. Small Craft Advisory until 6 PM EDT Friday for ANZ254>256.
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&& $$ SYNOPSIS...Nocera/EVT NEAR TERM...NMB SHORT TERM...EVT LONG TERM...Nocera AVIATION...Nocera/EVT/NMB MARINE...Nocera/EVT/NMB

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