Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 122144 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 444 PM EST Thu Jan 12 2017 .SYNOPSIS...
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A cold front moves through Southern New England tonight, followed by a drying and cooling trend overnight. Arctic high pressure builds into the Great Lakes Friday and then into New England Saturday. This will support a return to colder than normal weather across the region Friday night and Saturday. A reinforcing surge of cold dry air arrives Sunday as High Pressure exits Quebec into Maine. A cold start to the week Monday morning but a warming trend for the remainder of next week along with showery weather from time to time.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Low pressure mid afternoon was moving off toward Newfoundland, and swinging a cold front through the St Lawrence Valley and Northern/Western New York. The upper flow will continue to move this east and southeast this evening and tonight. Movement of the front would extrapolate it to the Connecticut River Valley around 9 PM/02Z, Worcester/Central Hills 1030 PM/0330Z, and the BOS-PVD corridor around midnight/05Z. Expect wet weather in much of Southern New England through the early night. Radar mosaics show a broad area of rain across NY and NW Pennsylvania. This is moving ENE into New England. Within this rain is a line of convection over western PA moving ENE leading the front. Several lightning strikes along this line in Western PA and Central Ohio. This line, if it holds together, extrapolates to the CT Valley about 7 pm and to the coast by 9 pm. Still strong winds overhead at 2000-3000 feet AGL, so we will continue to be concerned with gusts 30-35 knots in any heavier rain through the evening. Once the cold front moves through... the rain will end, the winds will shift from the west and eventually the northwest. Skies will clear, mainly after midnight. Temperatures should remain mild this evening, but then turn colder after the cold front moves through. Temperatures upstream early this morning were in the 30s and low 40s, which will be our min temp forecast for us tonight. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday... High confidence. Northwest winds will bring cold advection to the region through the day. Mixing is forecast to 925 mb. Temps in the mixed layer at 12Z would support max sfc temps of 40s except mid to upper 30s in western MA. Temps aloft at 18Z would support max sfc temps in the upper 20s and 30s. So we expect max temps to occur during the morning with falling temps much of the day. Cold advection mixing will also bring wind gusts of 25 to 30 knots to the surface. The airmass will be dry, but with some lingering moisture around 900 mb. That should be enough for a few diurnal clouds. Otherwise a sunny day with the aforementioned wind and falling temps. Friday night... High confidence. High pressure builds over the region with clear skies and light winds. Increasing high-level moisture suggests some increasing cirrus late at night. For the most part it will be a good radiational cooling night. With dew points in the single numbers, plenty of room for min temps of 5F to 15F. We undercut guidence by about 3 degrees. && .LONG TERM /SATURDAY THROUGH THURSDAY/...
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Updated 445 pm... Highlights... * Mainly dry but cold this holiday weekend * Warning trend next week but showery weather at times * Winter on spring break until the end of the month? Saturday/Sunday/Monday... Cold start to the weekend as 1040 mb arctic high pressure settles over the region Sat. -12C air at 925 mb over the area combined with subsidence inversion will preclude much if any adiabatic warming. Only good news is that weak pressure gradient will support light winds, thus no wind chills to speak of. Sided with the coldest guidance given these factors which will limit highs Sat to the mid and upper 20s. As for late Sat into Sat night...all model guidance has confluent flow over New England suppressing deep layer moisture to the south coast and offshore with next system. 12z ECMWF is farthest south, 12z farthest north and GFS in between. FWIW new 18z has shifted farther south. Perhaps more importantly both ensemble systems...12z GEFS and 12z EPS have trended farther south too. Thus our new pops reflect this trend with mainly a dry forecast Sat aftn and evening with just a low risk of flurries or a period of light snow from BID/MVY to ACK. Another northern stream trough zips across southern Quebec into New Brunswick Sunday with corresponding 1033 mb High advecting into Maine. This will deliver a reinforcing surge of cold air into the region for Sunday/Sunday night...then lingering into Monday. However this will support dry weather both Sun and Mon. As for temps, given radiational cooling potential both Sat ngt and Sun ngt have sided with the colder MOS temps. Tuesday thru Friday... The Southeast/Subtropical Ridge builds up the eastern seaboard next week. This shifts the storm track west of New England...supporting warm sector airmasses to overspread southern New England. FWIW 12z EPS has up to 50% of highs 50+ Wed/Thu and Fri. Interestingly a blend of all guid supports highs near 50 each of these days. Thus well above normal temps likely mid to late next week. As for precip, impossible to time individual waves but deterministic and ensemble guidance supports multiple precip events next Tue thru Fri. Given amplitude of southeast ridge and thermal profiles ptype looks wet and not white. In fact Euro ensembles (EPS) indicate warm southeast ridge influencing our weather at least thru day-10 and the ridge not eroding until late in the month!
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&& .AVIATION /22Z 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 Night/... Tonight... Moderate confidence. Broad zone of light rain from Southern Vermont through NY and NW PA. Movement along the line is toward the northeast, but with time later this afternoon and evening it will slide southeast across MA-RI-CT. Cloud bases ahead of this rain are VFR, but in the cloud layer we note a lower cloud layer around 1500-2500 feet and expect this to move through with the rain during the evening and early night. In addition, strong winds continue around 2000 feet AGL with speeds of 40-50 knots. This will continue to create low level wind shear through early tonight. A cold front trails the rain, and will sweep across MA-RI-CT tonight after 10 pm. Winds will shift from the west behind the front. Ceilings/vsbys will then improve to VFR for the remainder of the night. Friday-Friday night... High confidence. High pressure builds over the region. The increasing air pressure and movement of cold air into New England will cause brisk wind and will draw stronger winds to the surface from 3000 feet AGL. Expect NW wind with gusts 25 to 30 knots during the late morning and afternoon. Winds will diminish at night. KBOS TAF...VFR with LLWS. Ceilings will lower to MVFR levels this evening and early night as an area of rain moves through. Timing of the end of the rain is approximately 11 PM but with low confidence. A cold front follows, with wind shift and improvement to VFR. KBDL TAF...VFR. Ceilings will lower to MVFR levels late this afternoon and evening as an area of rain moves through. Timing of the end of the rain is approximately 10 PM, but with low confidence. A cold front follows, with wind shift and improvement to VFR. Outlook /Saturday through Tuesday/...Moderate confidence. Updated 445 pm... Saturday/Sunday/Monday...VFR and light winds. Tuesday and Wednesday...MVFR and/or IFR likely along with scattered showers and patchy fog.
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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 Night/... Tonight... Southwest winds have had observed winds in the 20s and around 30 knots. Expect the gusty winds to continue through the evening as a cold front approaches. This front will bring a period of reduced vsbys in rain, although with the best chance on Massachusetts Bay and Ipswich Bay and the outer waters to the east. The cold front will move across during around midnight, at which point the winds will shift from the west and northwest and diminish. Seas of 5 to 10 feet the first part of the night on the exposed waters, but these will subside overnight after the cold front and wind shift move past. Small Craft Advisory continues. Friday... Northwest winds will have potential gusts to 30 knots through much of the day. Lingering 5 to 7 foot seas, mainly on the outer waters and also on RI Sound. Small Craft Advisory in effect on all waters. Friday night... Winds and seas diminish Friday night as high pressure builds over Southern New England and the waters. Small Craft Advisory coverage will diminish through the night. Outlook /Saturday through Tuesday/...Moderate confidence. Updated 445 pm... Saturday thru Monday... Fairly light winds with high pres over or near the region. Dry weather and good vsby. Tue and Wed... Low pres tracking west of New England will bring a return to SSW winds to the coastal waters. Vsby limited at times in scattered showers and patchy fog.
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&& .CLIMATE... The following climate records have been tied or broken... BOS 61 tied old record 61 set in 1975 and 1913. ORH 57 broke old record 55 set in 1980. PVD 60 broke old record 59 set in 1975. Meanwhile... BDL 56 at 2 pm...record is 57 set in 1913. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EST Saturday for ANZ231>234- 251. Small Craft Advisory from 10 AM to 7 PM EST Friday for ANZ230- 236. Small Craft Advisory until 10 PM EST Friday for ANZ235-237. Small Craft Advisory until 5 AM EST Saturday for ANZ250- 254>256.
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&& $$ SYNOPSIS...WTB/Nocera NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Nocera AVIATION...WTB/Nocera MARINE...WTB/Nocera CLIMATE...Staff

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