Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271928 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 328 PM EDT FRI MAY 27 2016 .SYNOPSIS... Hot and hazy conditions continue with a low risk for showers or thunderstorms late today and again late tomorrow. A backdoor cold front will bring cooler temperatures to eastern MA Sunday but it will remain very warm across the interior, where hit and miss showers and thunderstorms likely develop during the afternoon. The potential exists for a period of heavy rain very late Sunday night into Memorial Day. Dry weather likely follows Tuesday through Thursday, with above normal temperatures trending back to seasonable levels by late in the week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A very warm and hazy day continues thanks to modest but apparent mid lvl ridging across srn New England. Upstream, noting a CU field and some shra/t-storms developing where airmass is more unstable /cooler aloft and more moist in the low lvls/. This is not expected to push much further E than the Berkshires through the evening, as the more stable/capped airmass remains in place across our region. Still have a few slight chance pops for this risk. Overnight, expect another mild and partly cloudy night with the remnant clouds from upstream convection moving over during the early morning hours. Noting current dewpoints vs SSTs still in the 50s, and an area of stratus/fog in the Gulf of Maine per latest VIS imagery, will likely see another round of fog especially along coastal areas /SE MA again/ and more areas inland overnight. This could once again be locally dense, and may require a dense fog advisory once confidence is higher in its location. Otherwise, mins only fall into the low-mid 60s again tonight thanks to high crossover temps and lingering clouds. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Tomorrow... Mid lvl ridging continues with rising heights across the region and plenty of sunshine. No trouble mixing to at least H85 where temps will approach +16C by afternoon peak heating. Weak return flow will limit sea breezes to mainly the south coast. Therefore, still expecting probably the hottest day we have seen thus far with highs topping out in the low-mid 90s across much of the region away from S coastal areas. Dwpts will remain elevated as well, mainly in the low-mid 60s even during peak mixing. The other issue will be convective potential. Plenty of SFC/mixed lvl CAPE would be available, except the rising heights and modest subsidence it/s associated with is likely to yield a slight capping inversion and limit updraft development. Lapse rates are modest, mainly approaching 6.0C/KM in the mid lvls, but this is most likely a reflection of the mid lvl dry air. Even the latest 12Z ECMWF now is almost NIL for QPF during the afternoon and evening hours. Definitely not going NIL given the rising PWATs and potential energy available if the cap is broken, but will limit it mainly to slight and low end chance across the terrain and along developing sea breezes where at least some lift will be available. T-storms will be mainly airmass-type as shear is also quite limited. Tomorrow night... Continued increase in low-mid lvl moisture will actually help to erode the cap and allow for some maintenance of any shra/t-storms that develop, so will be slow to drop overnight POPs. Otherwise, the increase in moisture beneath the inversion increases the risk for overnight fog development which once again has the risk of being locally dense at times and may require headlines. Otherwise, another mild night with mins only falling back into the 60s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Turning cooler Eastern MA coast Sunday but still very warm inland * Hit and miss showers/t-storms likely across interior southern New England Sunday afternoon/early evening * Period of heavy rain possible very late Sunday night into Memorial Day with even a small risk of localized flooding * Dry weather Tue into Thu with above normal temps trending back to seasonable levels late in the week Details... Saturday night...Isolated to widely scattered showers/t-storms may linger into the evening but should be on the downward trend with the loss of daytime heating. Otherwise, expect mainly dry weather Saturday night but it will be quite mild and muggy for late May. Low temps may only drop into the middle to upper 60s for many locations away from the cooling marine influence of the south coast. Patchy fog likely develops in the typically prone locations with dewpoints in the 60s. Sunday...Still timing differences with the backdoor cold front but appears that it will still be east of the CT River Valley by mid afternoon. So its conceivable that Sunday afternoon temps will have fallen into the 60s along the Eastern MA coast, while the Lower CT River Valley might be in the lower 90s. The morning should mainly be dry, but expect 1000 to 2000 J/KG of Cape to develop across interior southern New England. Despite upper level ridging, decent low level convergence/instability will allow low level moisture to pool a bit. The result should be hit and miss showers/thunderstorms developing across interior southern New England Sun afternoon. The extent of this activity will be determined by how fast the front moves and amount of instability that is able to develop. Highest risk for scattered activity is across western MA/northern CT but it could extend back into portions of central MA/RI if front moves slower. 0 to 6 km shear is weak, so overall severe weather threat is low. However, given decent instability can not rule out a strong thunderstorm or two. Any storms that develop will be slow moving and capable of producing very localized heavy rain. So to sum up Sunday, dry weather expected for much of the day but scattered showers/t-storms likely develop in the afternoon across the interior. While activity should be hit and miss, very localized heavy rainfall and lightning will be the biggest concern with any storm. Sunday night and Memorial Day... Hit and miss convection across the interior should diminish Sunday evening with the loss of daytime heating. Mainly dry weather expected for the first part of the night. Things then become very interesting very late Sunday night into Memorial day. The National Hurricane Center is expecting low pressure between the Bahamas and Bermuda to develop into a tropical or sub tropical cyclone in the next 48 hours. While a direct impact will not occur, an approaching cold front will likely pull a plume of its tropical moisture northward. PWATS may rise to around 2 inches in southern New England. Still plenty of uncertainty on how this unfolds, but a period of heavy rain showers and a few embedded thunderstorms are possible across the region. Fortunately, this appears to be a progressive event but given tropical connection there is a small risk of some localized flooding. Something will have to watch closely, especially given it will be on the end of a Holiday Weekend and a big travel day. Tuesday through Thursday... Looks like dry and warm weather follows behind the cold front on Tuesday with highs mainly in the 80s. It is a long way off, but current guidance favors dry weather Wed into Thu as high pressure builds down from the Canadian Maritimes. This would also generate an easterly low level component to the wind with temperatures likely returning to seasonable normals by Thursday. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 00z...high confidence. VFR conditions continue with a low risk for afternoon shra/t-storms mainly across the CT valley and points W. Tonight...moderate confidence. Mainly VFR through about 06Z inland, then patchy fog possible especially at typically prone airports with localized MVFR/IFR conditions. Another risk for LIFR along Cape Cod and Island terminals overnight into tomorrow morning. Saturday and Saturday night...moderate confidence. Mainly VFR. Local MVFR-IFR conditions in patchy fog through mid morning. Low probability of brief MVFR conditions in SCT afternoon SHRA/TSRA across the interior. Another risk for overnight fog tomorrow night. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Sunday through Wednesday/... Sunday...Moderate confidence. VFR conditions may lower to MVFR thresholds across Eastern New England behind backdoor cold front. Otherwise, mainly VFR across the interior but briefly lower conditions possible in hit and miss showers/t-storms during the afternoon. Sunday night and Memorial Day...Moderate confidence. MVFR-IFR conditions may develop late Sunday night into Memorial Day in a period of rain showers which may be locally heavy. Monday night and Tuesday...Moderate to high confidence in mainly VFR conditions. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Will be dropping the small craft advisory as it appears seas will generally not build as high as previously forecast. Winds still remain mostly S-SW with gusts only to around 20 kt near shore during the daylight hours. Therefore, mainly quiet boating weather is expected regarding mainly seas and winds. There will be some fog to contend with especially overnight and morning hours. This could be quite dense at times and may take some time to burn off even after sunrise. Outlook /Sunday through Wednesday/...High confidence. Winds and seas will generally remain below small craft advisory through the period with a relatively weak pressure gradient. Biggest concern for Mariners will be late Sunday night into Memorial Day, when a period of heavy rain showers/isolated thunderstorms are possible. && .CLIMATE... Still expect highest temperatures of the week on Saturday. Some record highs may be challenged. However, might even see temps getting close to records today as well. Record highs for Saturday May 28... Boston...92 set in 1931 Providence...91 set in 1931 Hartford...93 set in 1977 Worcester...88 set in 1911 and 1929 Milton/Blue Hill...90 set in 1929 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until 11 PM EDT this evening for CTZ002>004. MA...Air Quality Alert until 11 PM EDT this evening for MAZ002>006- 008>013-026. RI...Air Quality Alert until 11 PM EDT this evening for RIZ001>005. MARINE...None. && $$ SYNOPSIS...WTB/Doody NEAR TERM...Doody SHORT TERM...Doody LONG TERM...WTB AVIATION...WTB/Doody MARINE...WTB/Doody CLIMATE...staff

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