Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221858 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 258 PM EDT SUN MAY 22 2016 .SYNOPSIS... * Near- and Short-Term Forecast Updates only... 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 the weekend, especially in western sections. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Rest of today... Much of the area will remain dry beneath sinking air behind the departing coastal low into SE Canada. As observed via radar trends most if not all of the showery weather has concluded. Via satellite a lot of the low cloud decks have eroded with only some mid to upper level cloud decks lingering along the leading edge of mid-level vortex energy and remnant S moist flow. So only concern towards evening is to the N/W. Can not rule out that a combination of diurnal forcing along the leading edge of some mid level vortex energy around the broader trough pattern in an environment of steep lapse rates up to H7 yields shower and even possibly thunderstorm activity into the W CT River Valley. But will hold the activity just N/W outside of our forecast area. High terrain will be an influencing factor so can not rule out some development to the immediate N/W over the Berkshires. Just something to watch out for towards sunset. Chance PoPs accordingly. Scattered to broken cloud decks continuing with temperatures topping out around the mid to upper 60s. Tonight... 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 probabalistics 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 the weekend, especially in western sections. Overview and Model Preferences... Upper level low pressure passes northeast from the Mid-Atlantic coast, reaching the Gulf of Maine Tuesday night. By Thursday and Friday, and continuing into next weekend, a strong upper level ridge develops over the Mid- Atlantic states...extending northward into western New England. In general, models are in good agreement at the upper level features but differ somewhat on timing and location of possible convection later in the week. All agree on a major warmup to summertime levels. There will also be increasing moisture. A warm frontal boundary could provide the focus for scattered thunderstorms Thursday as it moves northward. Scattered showers or thunderstorms will be possible during the afternoons and evenings into the weekend. Details... Monday night into Tuesday... Core of the upper level cold pool moves over southern New England Mon night into Tue...with -18C at 500 mb...which is cold but not that extreme. Models are now in better agreement on the track of surface low pressure, which moves between outer Cape Cod and the benchmark of 40N 70W on Tue. The ECMWF, which had it moving into RI, is thus a bit less unstable than it was. We will need to keep an eye on the possibility of some nocturnal thunderstorm activity for southeastern MA and RI Mon night. All models show a rapid influx of unstable air into southeastern sections between midnight and daybreak Tue. Total Totals Indices reach 55 and there is an indication of very unstable lapse rates of 7C from 700-500 mb. 0-6 km bulk shear values increase to 45-55 kts from the south-southeast at that time, too. However, with cool northeast surface flow, there is no Convective Available Potential Energy (CAPE). This is not the usual situation to expect a chance of thunderstorms, but we have veering of wind with height (WAA) and increasing speeds with height... so, could see some organized, but scattered and elevated thunderstorms, especially RI and southeast MA late Mon night. Scattered showers or an isolated thunderstorm will gradually move away by Tue evening. Highs Tue will hold in the 65 to 70 range due to cloud cover 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 with highs in the lower 80s away from the coast. There could be sea breezes, 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 hold in the upper 60s to lower 70s. Thursday through Saturday... On Thursday, 925 temps warm to +21C, so am forecasting mid 80s in the CT valley and 80-85 elsewhere, cooler at the coast. A warm front extending eastward from low pressure in western NY may provide the focus for scattered showers and thunderstorms Thu afternoon and evening. The GFS shows an axis of 36 K Index, indicating a lot of moisture and instability, extending eastward along the MA/CT/RI border by 00z. ECMWF, however, keeps it all to our west. So will go with chance PoPs for now. Warm weather with highs in the 80s are expected Friday and Saturday with a front mainly north of the area. Diurnally-driven showers and thunderstorms are possible both days, especially across the western half of southern New England. && .AVIATION /19Z SUNDAY 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/... 18z update... Today and Tonight...High Confidence. Trying to keep optimistic but surprised as how IFR is lingering across SE coastal terminals. May remain the norm with NE winds gusting around 25 kts through the overnight period with the additional threat of DZ/-RA. Otherwise all other terminals VFR with light N/NE winds. Low-end VFR cigs. Lesser confidence MVFR. Also watching N/W terminals only for this afternoon as to the possibility of SCT SHRA and low risk TSRA. 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. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 3 pm update... 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 Thursday...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 11 PM EDT this evening for ANZ231>234. Small Craft Advisory until 5 AM EDT Monday for ANZ235-237. Small Craft Advisory until 6 PM EDT Monday for ANZ250-251- 254>256. && $$ SYNOPSIS...Sipprell/GAF NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...GAF AVIATION...Sipprell/GAF MARINE...Sipprell/GAF is the U.S. government's official web portal to all federal, state and local government web resources and services.