Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 242303 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 703 PM EDT TUE MAY 24 2016 .SYNOPSIS... Scattered showers will continue across portions of Southern RI and southeast MA early this evening as low pressure slowly moves across southeastern New England. An upper level high pressure ridge will then bring very warm to hot weather to most of the region Wednesday through Saturday, except for cooler temperatures at times on the immediate coast. A few showers and thunderstorms are possible Thursday night into Friday, but a better chance exists Saturday afternoon and evening ahead of a backdoor cold front. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 700 PM Update... Overall forecast is on track. Removed the thunder mention for this evening as convection has remained just west of southern New England. Also increased precip trends across RI and southeast MA as area of showers continues to develop and spin as the upper level low begins to slowly shift eastward. Otherwise breaks of sun across western MA as allowed for temps to warm in to the upper 60s late this afternoon. Onshore flow across eastern MA will continue until the low shifts eastward creating more of a northerly flow. Fog and drizzle will remain over the next several hours. May need to watch for radiational fog development tonight across the low lying areas as lingering low level moisture combined with cooling temperatures will create a low temp/dewpoint spread. Dense fog is not expected at this time. Previous Discussion... An area of showers may develop over Southern-Southeastern RI into Southeast MA as plume of deeper moisture pivots northeast off the ocean into that area. This is supported by multi model K indices and latest trends seen on water vapor satellite imagery. Already seeing the first signs of this with light showers developing over Marthas Vineyard and Elizabeth Islands. However these showers should be weak/low top with not a lot of impact. Thus not a washout expected this evening. Otherwise drying trend second half of the night as vertically stacked low moves offshore by sunrise. Temps seasonably cool tonight with lows in the upper 40s to low 50s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... *** Summer-like Temperatures Arrive Wednesday *** 4 pm update ... Wednesday ... Vertically stacked low just east of Cape Cod at 12z/8am but ejects seaward quickly with rising heights and northwest flow aloft by midday. Thus any cloudiness across Eastern MA at sunrise quickly erodes and/or moves offshore with abundant sunshine for the afternoon. Warming temps aloft to +14c at 850 mb and +21c at 925 mb yields surface temps at least 30C/86F. Although with boundary layer mixing beyond 850 mb highs will make a run at 90 in many locations. However humidity will be low with dew pts only in the mid to upper 40s. Not as warm along the South Coast including Cape Cod and the Islands...where winds will bend to the southwest off the cooler ocean waters. Wed night ... Dry, tranquil weather with mid level ridge and associated anticyclonic flow continuing to build across the region from the west. Dry airmass in place along with diminishing winds and mostly clear skies will allow temps to fall into the 50s...except 60-65 in the urban areas. && .LONG TERM /THURSDAY THROUGH TUESDAY/... HIGHLIGHTS... * Well above average temperatures for Thu and Fri with the potential for a spot thunderstorm * Hazy, Hot and Humid for Saturday with locations reaching 90+F * Scattered showers and thunderstorms are possible on Saturday * Back door cold front on Sunday will keep conditions cool into Monday OVERVIEW... Large scale pattern is in agreement with both determinisic and ensemble guidance. Upper level trough will move eastward towards the Maritimes as Midwest ridge builds into the Northeast. Anomalous high pressure over the western Atlantic will continue to build this ridge through Saturday. Anticipate summer-like warmth and humidity to return to the region as ensembles show both the 700 and 500 heights nearly 1-2 standard deviations above normal. Several waves will move through the flow keeping a chance of showers and thunderstorms in the forecast for Late Thursday and again on Saturday. Because of the mesoscale differences in the guidance trended the forecast towards an overall blend. Back door cold front will swing through by Sunday cooling the area down. However, on Monday, still some discrepancies with offshore high pressure. The GFS keeps it closer to the coast keeping temps on Monday cooler while the EC is weaker and more offshore. Continued with a model blend for now. DAILIES... Thursday into Friday...High Confidence. Upper level ridge will build into the region on each day. Anticipate the warm weather to continue into Thursday as 925 mb temps are generally around 20C. This warm airmass combined with westerly flow and the warm May sun will help aid in high temps reaching into the mid to upper 80s with a few 90s near the CT valley. Conditions look to be cooler along the MA coastline as a sea breeze will develop from weak winds aloft. A spot shower or thunderstorm may develop in the afternoon, but most of the region will remain dry. Weak shortwave will pass through the flow Thursday night. Due to building heights across the region and weak southwesterly flow, appears that the better forcing will be north of southern New England. However, cannot rule out the potential for precip Thursday night into Friday morning across the north and northwest portion of the region. Guidance continues to highlight the potential for elevated convection so continued the mention for thunder in the forecast for now. Temperatures on Friday look to be similar as they will be on Thursday with heights in the mid to upper 80s with a few 90F across the CT valley. Still a large spread in the guidance on if Boston will reach 80F as there is question in the sea breeze development. However 925 mb winds appear to be strong enough to allow for good SW flow to warm the immediate eastern coastline. This southwest flow will keep the south coast cooler thanks to onshore flow and the cooler ocean waters. Once again a spot shower looks to be possible in the afternoon, but better forcing and instability appears to remain west of the region. So another dry weather day is expected. Saturday...Moderate Confidence Upper level ridge will strengthen across the the eastern Great Lakes as warm front lifts northward. A very warm day will be on tap as 925 mb temps will warm to 23-24C. Ensembles continue to show probabilities that many locations could reach above 90F. This hazy, hot and humid day does have some caveats. Approaching surface trough looks to trigger afternoon convection for the region. Some storms could be strong or severe, but a bit to early to tell. Sunday into Monday...Moderate Confidence. Back door cold front will swing through the region late Saturday night into Sunday. This will cool temperatures down across the region. The front does look to push and stall across the Hudson. However, could still see upper 70s or low 80s across the CT river valley as 925 mb temps are between 18-20C. Otherwise anticipate a cooler weather day. Still large spread for surface temps on Monday. GFS and EC have about a 15 degree difference amongst each other. The GFS is cooler with highs in the low 70s while the EC is warmer with highs in the low 80s. Continued with a model blend for now to split the difference. May see a few sct showers on Monday depending on the location of the southeast low pressure system and how quickly it moves northwards towards the region. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight ... Moderate confidence with uncertainty centered around except timing of improving conditions overnight. Isolated lighter showers east of the Worcester Hills tonight. Mainly MVFR all terminals except Coastal MA which will see periods of IFR. VFR across the CT valley. Cigs and vsby improve from west to east after 06z. Wed ... high confidence. Any leftover MVFR cigs at sunrise will be across Eastern MA but quickly lifting to VFR by 15z or sooner. Dry weather and west winds except southwest along the coast. Wed night ... high confidence. VFR/DRY and light sw winds becoming west. KBOS TAF ... Moderate confidence. Some uncertainty on exact timing of improvement but should take place around 06z. KBDL TAF ... Moderate confidence. Some uncertainty on exact timing of improvement but should take place around 03z-06z. Outlook /Thursday through Sunday/... Thursday...High confidence. VFR. Thursday night and Friday...Moderate confidence. VFR conditions likely dominate but some brief MVFR conditions possible in a few showers/t-storms mainly across the interior. Saturday...Moderate confidence. Mainly VFR conditions but brief MVFR- IFR conditions possible Saturday afternoon/evening in scattered showers and thunderstorms. Sunday...Low confidence. MVFR conditions to start with some improvements on Sunday as a back door front swings through. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 4 pm update ... Tonight ... high confidence except uncertainty on areal coverage of showers and exact timing. Vertically stacked low over the RI waters will slowly drift to Cape Cod by morning. Few light rain showers will accompany this low along with patchy fog. Leftover southeast swell of 3-6 ft continue across the Southeast MA ocean waters. Wed ... high confidence on all weather parameters. Low pressure near Cape Cod at sunrise moves east/offshore by midday with a drying trend and vsby improving to the horizon. Winds become southwest by midday. Wed night ... high confidence. Light southwest winds become westerly. Dry weather and vsby continue. Outlook /Thursday through Sunday/...High Confidence. Winds and seas will remain below Small Craft Advisory thresholds the majority of the period. Could see some brief near shore southwest wind gusts of 15 to 20 knots are possible Friday and Saturday...which will result in some choppy seas. Otherwise could see some afternoon convection on Saturday as a back door cold front swings through. && .FIRE WEATHER... 4 pm update ... Wednesday ... High temperatures soaring well into the 80s to near 90 in most locations will result in minimum afternoon RH values dropping to between 20 and 30 percent. A few hours of westerly wind gusts of 20 to 25 mph are anticipated. Given this morning`s rainfall and marginal criteria, will probably fall short on the need for fire weather headlines especially given many locations are near full green-up. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Air Quality Alert from 11 AM to 11 PM EDT Wednesday for MAZ020>024. RI...Air Quality Alert from 11 AM to 11 PM EDT Wednesday for RIZ003- 004-006>008. MARINE...Small Craft Advisory for hazardous seas until 4 AM EDT Wednesday for ANZ254-255. && $$ SYNOPSIS...Nocera/Dunten NEAR TERM...Nocera/Dunten SHORT TERM...Nocera LONG TERM...Dunten AVIATION...Nocera/Dunten MARINE...Nocera/Dunten FIRE WEATHER...

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