Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222343 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 743 PM EDT SUN MAY 22 2016 .SYNOPSIS... Dry tonight into the early half of Monday, before a second area of low pressure moves up the coast and ushers in wet weather through Tuesday. A significant warmup will occur Wednesday, continuing into next weekend. Scattered showers or thunderstorms are possible from Thursday into next weekend, especially over western sections. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Main axis of showers expected to stay well west of southern new England. Did note a lone shower in central Hampshire county moving southwest. This shower may impact western Hampden county before 8:30 pm. With sunset fast approaching, not expecting more showers to develop. Brought the forecast back in line with observed trends, especially sky cover. Previous discussion... An overall quiet forecast period. Initial coastal low lifts NE into SE Canada as a secondary coastal low emerges off the Mid-Atlantic in response to N stream energy diving S, cutting off from the main mid- latitude flow. Between the two systems looking at scattered to broken cloud decks with light N winds albeit a bit more brisk over E/SE coastal MA with the possibility of some drizzle or light showery weather per cold conveyor belt motions. Dry W with isentropic downsloping NW to SE. Lows milder E/SE with anticipated socked in conditions, around the 50 degree mark, while mid to upper 40s with partial clearing W. Otherwise, a high risk of rip currents continues into this evening along the eastern portions of Cape Cod and Nantucket, as well as along the south coast, from Bristol County, MA to Westerly, RI. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday... A return of wet weather. Coastal low off the Mid-Atlantic gets wound up and pulled back, occluding towards the N and W beneath the mid to upper level low. Will see an increase in wet weather and clouds as a result of several factors. The first per a trowaling confluence of conveyor belts as mid-level vortex energy parent to the mid to upper level low pushes N. Parent forcing on the increase along with an isallobaric NE wind results in high-end chance to likely PoPs late. The second per vortex energy stretched and inverted N of the low maintaining low level confluence across Upstate NY and PA E into the CT River Valley. Cooler air aloft yielding steeper lapse rates in an environment of favorable lift, with any diurnal forcing especially with sunshine we would likely see some shower activity emerge. Focus especially along the high terrain with orographic influences upon convergent flow. The likely window of partial clearing more likely N and W just prior to increasing cloud and PoP chances late should allow highs to warm into the low to mid 70s. Cooler E and SE with increasing NE onshore flow. Will follow closely to ensemble probabilities with regards to PoP chances in such a chaotic pattern that has been poorly handled by a majority of the forecast guidance. Monday Night... Surface low continues to back and occlude beneath the cutoff mid to upper level low pulling N and across S New England in response. In its mature to dying phase conveyor belt motions undergo strong forcing across much of S New England within the comma head of the low itself. This prior to drier air wrapping into and cutting off the system. Likely PoPs warranted early, perhaps diminishing into morning. Will need to monitor SE New England for the possibility of an elevated convective setup. Weak instability but strong shear, convective indicies exceeding respective thresholds, can not rule out a rumble of thunder for SE communities but have low confidence with regards to a severe threat with any convection. Abundance of clouds and moisture with a continued E/NE flow, looking at lows in the low to mid 50s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights... * Good chance of showers Tuesday * Significantly warmer Wednesday into next weekend * Scattered showers and thunderstorms Thursday into next weekend, especially over western sections. Overview and Model Preferences... Very good agreement in the latest guidance suite in moving a persistent upper low toward the Maritimes by late Wednesday afternoon. Strong ridging over the north Atlantic edges west over the southeast USA late this week. This will mean more summer-like conditions late this week into next weekend. With the increasing heat and humidity, also expecting the possibility for diurnal showers and thunderstorms, each day. Subtle, but significant, differences in the details Friday into next weekend. The predictability of these details is rather low, so will favor a consensus approach, for now. Details... Tuesday... Core of the upper level cold pool moves over southern New England. Still differences in the specific low tracks among the latest models, so confidence is not high on this particular aspect, yet. Guidance does agree on a low pressure passing close enough to southern New England where we would need at least a chance for some showers in the forecast. We will need to keep an eye on the possibility of some thunderstorms, too. While the cold pool aloft will mean an unstable atmosphere, the northeast onshore flow should limit the available energy to put into thunderstorm updrafts. Expecting below normal temperatures due to abundant clouds and scattered showers. Wednesday... Brief ridge of high pressure to our south takes over, leading to downslope air flow, drier conditions, and more summer-like temperatures away from the coast. There could be seabreezes, but it appears the synoptic flow could be just strong enough to prevent lower temperatures along parts of the MA east coast. Cape Cod and the islands, as well as Cape Ann, however, will likely remain as cool as the south coast of New England, where southwest winds should prevail. Thursday through Sunday... This still appears to be a prolonged period of summer-like heat and humidity, especially away from the coasts. The questions to be answered during this portion of the forecast are: where will a frontal boundary be between Thursday and Friday, and how quickly will it move? A scenario can be seen where we wind up on the cold side Friday, which would mean lower temperatures and a greater risk for showers. Diurnal showers, and perhaps some thunderstorms, are expected through most of this period. The position of this front will have a large impact on chances, and is one of the more uncertain aspects of this forecast. Will keep a chance for showers in the forecast until this critical detail can be better worked out. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/... Tonight...Moderate Confidence. Mainly VFR across southern New England this evening. With onshore northeast flow, cannot rule a return to local IFR in stratus, drizzle and/or fog. As winds shift more north than northeast, the risk for IFR conditions will decrease, except across the outer Cape and Nantucket. Monday...Moderate Confidence. Low-end VFR cigs with MVFR across E/SE coastal terminals. Will heighten the risk of IFR to moderate keeping it confined to SE coastal terminals. -SHRA developing late, focus along the S coast as well as the N/W interior out into the CT River Valley. NE flow prevailing with gusts up to 20 kts especially over the E/SE coast. Monday Night...Moderate Confidence. -RA likely for all terminals. Deteriorating conditions into the evening hours and prevailing overnight. Mix of MVFR down to LIFR with NE winds prevailing, gusts upwards of 20 kts especially across the E/SE coastal terminals. A final note, there is a low risk of TSRA for SE coastal terminals. KBOS TAF...Pulling out MVFR and keeping cigs VFR with the low-end of the spectrum SCT per webcams shortly before 18z. Not much issue in thinking with landing on the 4`s if that be the case with NE winds prevailing, gusts up to 15 kts. KBDL TAF...Becoming SCT and dry and such trends should continue into the overnight hours. N winds with gusts limited to 15 kts. Will see a return of low cigs and wet weather late Monday with a continued downward trend into Monday night. Outlook /Tuesday through Friday/... Tuesday...Moderate Confidence. Scattered showers will continue across the area with NE flow. An isolated TSRA is also possible. This also suggests low clouds. Therefore, periods of MVFR/IFR are likely, but it`s possible that occasional VFR will occur, especially across the interior. Wednesday...High Confidence. Mainly VFR. Thursday...Moderate Confidence. Mainly VFR. Scattered MVFR in scattered showers and thunderstorms, mainly west of KLWM-KORH-KIJD. Friday...Moderate Confidence. Mainly VFR. Scattered MVFR in scattered showers and thunderstorms. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...High confidence. Coastal low lifts into SE Canada behind which NE winds diminish. Seas remain 5 to 9 feet resulting in small craft advisories on the outer waters. Monday into Monday Night...Moderate confidence. Second coastal low moves up the coast through the day with impacts towards late. Into evening will see increasing areal coverage of rain along with NE winds. Restrictions to visibility with the wet weather along with gusts up to 20 kts. Seas maintain 5 to 7 feet. Small craft advisories continue. Outlook /Tuesday through Friday/... Tuesday...Moderate Confidence. Secondary low lingers with subsequent wind and S swell. Seas may reach 7 to 8 feet south of Nantucket. Small craft advisories may need to continue for some waters. Wednesday into Friday...High Confidence. High pressure briefly builds over the waters. Mainly quiet boating weather is expected with winds and seas below Small Craft Advisory levels. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Rip Current Risk until 10 PM EDT this evening for MAZ020- 022-024. RI...High Rip Current Risk until 10 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 2 PM EDT Monday for ANZ231-251. Small Craft Advisory until 2 AM EDT Monday for ANZ235-237. Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254-255. Small Craft Advisory until 8 AM EDT Monday for ANZ256. && $$ SYNOPSIS...Belk/Sipprell NEAR TERM...Belk/Sipprell SHORT TERM...Sipprell LONG TERM...Belk AVIATION...Belk/Sipprell MARINE...Belk/Sipprell

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