Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 241820 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 220 PM EDT Sat Sep 24 2016 .SYNOPSIS...
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* Updates to near- and short-term forecast portions only... Cool and dry weather this weekend will continue into early next week. A slow-moving low pressure and cold front could lead to some showers late next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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230 pm update... Some decent N winds persisting across the region with deep-layer mixing of the boundary layer, with the mix-down of drier air and faster momentum. Expect scattered cumulus to persist along with these conditions towards sundown. Temperatures on track with highs up around the upper 60s. Stepping the temperatures a degree or two higher than originally thought. Some indication perhaps as to the strength of the late Summer / early Autumn sun plus how dry conditions are across the region. Tonight... High pressure building into the region from the north and west. Radiational cooling setup as the boundary layer decouples allowing for winds to become light beneath clear conditions. Though still a decent pressure gradient along the E/SE coast yielding some coastal and offshore NW winds thereby making it milder. Forecasting lows around the upper 30s with coldest conditions over N/W MA with the likelihood of some frost, warmest over the E/SE shore. Focus upon areas which are prone to radiate.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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Sunday... Unseasonably cool and mostly sunny. Highs topping out around the mid to upper 60s as the coldest of airmass at H85 sweeps through the region, but still stepped up a degree or two given the sun angle and dry conditions across the region. Quite the Autumn feel. Worth nothing, such an H85 airmass, around +2C, close to the record lowest observed of just slightly below freezing per Chatham MA sounding climatology. Overall light winds but still a bit breezy along the E/SE coast. Went with deep-layer mixing of the boundary layer, so expect a mix down of drier air with dewpoints possibly into the 20s and breezy N winds along the E/SE coast with gusts up to 20 mph possible. Sunday Night... Given a chilly day and high pressure settling in over Central New England overnight, am going to lean very low and close to record low temperatures given the synoptic setup. This gives a forecast low temperature range around the low to mid 30s for much of Southern New England. See the climate section below for September 25th and 26th record low temperatures. Clear conditions, light winds overall. Am concerned. Thinking an anomalous situation given dry conditions across the region coupled with the radiational cooling setup. Wonder whether guidance is capturing this rather well. A hunch that perhaps there`s an opportunity here to undercut guidance by a couple of degrees. Feel Sunday morning lows, if lower than initially thought, will weigh on confidence and forecast thinking going into Monday morning. Rather than going with double-headlines, have kept with the frost advisories for tonight going into Sunday morning, while highlighting the Monday morning impacts in the hazardous weather outlook. Could be looking at headlines over much of Southern New England as frost conditions are possible in the E/SE interior of Massachusetts.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/... HIGHLIGHTS... * Areas of Frost possible Sunday Night across NW zones * Frontal system late Monday/Tuesday will bring widespread showers * More seasonable temperatures return by Tuesday Overview/confidence... High confidence in below average temperatures Sunday night into Monday. Model guidance is in better agreement then 24 hours ago with passing frontal system bringing precipitation to the region late Monday into Tuesday. Temperatures will turn more seasonable for the remainder of the week. Guidance does begin to spread by late Wed into Thursday. The EC builds the North Atlantic ridge stalling the upper level low over the Ohio Valley where at the GFS is a bit less amplified keeping the cut-off low over New England. This leads to difference in both temperature and precip chances. Continues with model blend until guidance becomes more inline. Sunday night into Monday...High Confidence. High pressure settles over the region Sunday night resulting in light winds and clear skies. This will allow for radiational cooling which could plummet temps into the low to mid 30s away from the urban centers and coastal regions. Frost advisories will have to be issued with the potential for a possible freeze warning for NW zones. Will hold off for now due to current frost advisory to avoid double headlines. High pressure will remain over the region for most of the day before sliding offshore by the evening. Sea breeze development is possible across both coastlines. Otherwise anticipate a mostly sunny skies for most of the day with temperatures warming into the mid to upper 60s. Monday night into Tuesday...Moderate Confidence. Upper level ridge will move overhead Monday night as WAA spills into the region. Overnight temps will begin to fall during the evening hours before remaining steady or even rising by the early morning hours. A few showers are possible during the overnight hours, but the bulk of the rain will move through on Tuesday. Ahead of the FROPA, temperatures will warm into low 70s across the area. Dewpoints will be on the rise as well making it feel a bit more humid. Appears the best timing will be Tuesday morning which could make way to a rough morning commute. GEFS continue to show 70- 80 percent probs of over a half of an inch of rain, so confidence is increasing in widespread rainfall. Lastly, a good pressure gradient behind the passing frontal system could result in gusty winds near 20-25 mph. Wednesday and Beyond...Low Confidence. Guidance begins to diverge within this timeframe as mentioned above. EC keeps the region more wet by late next week with the upper level low to our west. The GFS is a more dry scenario with perhaps a few diurnal showers within the cold core low over the region. Will continue with a model blend for temperatures but will keep the forecast dry for now until guidance spread decreases. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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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 Sunday Night/...High confidence. VFR. N/NW winds 20 to 25 kts especially during the daytime periods lingering into evening. Still breezy along the E/SE coasts overnight around 10 kts while light winds elsewhere. SKC. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday through Thursday/... Monday...High confidence. VFR. Sea Breezes along the coast. Monday night thru Wednesday...Moderate confidence. VFR through the period with localized MVFR in rain on Tuesday. Gusty winds southerly winds near 30 kts across East coastal terminals. Improving trend on Wednesday.
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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 Sunday Night/...High confidence. Today... Small craft boaters should be aware of the persistence of N winds upwards of 20 kts through much of today, settling towards evening under the influence of high pressure. Seas holding around 5 feet thus will continue the small craft advisories where the threat of 5 foot seas and gusts up to 25 kts is more likely. Tonight into Sunday... Resurgence of NW winds to near 25 kt will likely require near shore waters to once again have a small craft advisory, and continue the ocean waters. Seas will be the issue tomorrow, dropping from about 6-7 ft through the day. Outlook /Monday through Thursday/... High confidence in high pressure settling over the waters Sunday night into Monday. This will allow in lingering 5 foot seas to dissipate. Strong cold front will approach the waters late Tuesday. Ahead of the front southerly winds will increase just shy of gales with seas building as a response. Vsbys will drop within any heavy rain showers as the front passes. Winds and seas will relax by Wednesday as weak high pressure builds back over the waters.
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&& .CLIMATE...
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Record low temperatures... September 25th / 26th (last set in...) Boston ....... 38 (1950) / 34 (1879) Hartford ..... 30 (1963) / 33 (1978) Providence ... 36 (1963) / 37 (1967) Worcester .... 31 (1944) / 28 (1925)
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Frost Advisory from 2 AM to 8 AM EDT Sunday for MAZ002>004-008. RI...None. MARINE...Small Craft Advisory from 4 AM to 11 AM EDT Sunday for ANZ231>235-237-251. Small Craft Advisory until 3 AM EDT Monday for ANZ250-254-255. Small Craft Advisory until 4 PM EDT Sunday for ANZ256.
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&& $$ SYNOPSIS...Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...Dunten AVIATION...Dunten/Sipprell MARINE...Dunten/Sipprell CLIMATE...Sipprell

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