Area Forecast Discussion
Issued by NWS Boston, MA

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284 FXUS61 KBOX 250629 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 229 AM EDT WED MAY 25 2016 .SYNOPSIS... A few leftover showers may fall across western MA and north central Conn., as well as south coastal MA and RI through the early this morning as low pressure slowly moves northeast to the Gulf of Maine. 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 THIS MORNING/... 145 AM Update... H5 cutoff low has pushed just E of Cape Cod as seen on latest water vapor and IR satellite imagery. Winds have diminished to near calm away from the coast at 05Z obs. Noting patchy dense fog has started to form across portions of the CT valley into NE CT. May see more develop over the next few hours across central and western areas. May also see a few showers develop with the last of the band crossing out the Berkshires through 08Z-09Z. Remainder of previous forecast in pretty good shape, but have updated to bring current. Previous discussion... With light winds across the region, along with lowering temp/dewpoint spreads, will still see patchy fog develop along with lingering low clouds from around Worcester and Windham counties eastward through around midnight, but trends continue to indicate that this should slowly push E during the early morning hours as the low exits, but will be slowest across E coastal MA. Partial clearing should begin moving into the CT valley after midnight as winds back to light NW, then will slowly shift E overnight. Clouds will linger along the E coast through daybreak. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... *** Summer-like Temperatures Move in Today *** Today ... 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 NIGHT 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 /06Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 12Z...Moderate confidence, though lower in timing of improving conditions toward daybreak. Areas of IFR-LIFR CIGS and mixture of VFR to IFR VSBYS in patchy fog, lowest across interior E MA and portions of CT valley into NE CT. Should start to see conditions improve to VFR across CT valley after 08Z, then slowly progressing E after daybreak. Calm or light/vrbl winds. Today...Moderate confidence this morning, then high confidence. IFR CIGS and areas of MVFR-IFR VSBYS across central-E MA/RI should improve by mid morning. Otherwise, VFR. W-SW winds 10 kt or less. Tonight...High confidence. VFR conditions. W-NW winds less than 10 kt. Thursday...High confidence. VFR. Light W-NW winds, except sea breezes possible late morning/afternoon along the coast. KBOS TAF...Moderate confidence. Uncertain on exact timing of improvement, but should take place by around 10Z. KBDL TAF...Moderate confidence. otherwise VFR. Outlook /Thursday Night through Sunday/... 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. Through 12Z...High confidence. Upper level low will slowly move into Massachusetts Bay during the early morning hours. Light E-NE winds across the eastern waters will back to N-NW, becoming mainly W of all waters toward daybreak. Leftover SE swells will linger on the outer waters E and S of Cape Cod, but should subside below 5 ft by around 08Z- 09Z. Visibility restrictions in patchy fog, locally dense in some locations, should improve from W-E. Today...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. Tonight...High confidence. Light southwest winds become westerly. Dry weather and vsby continue. Outlook /Thursday Night 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... 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 today`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 this morning to 11 PM EDT this evening for MAZ020>024. RI...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for RIZ003-004-006>008. MARINE...Small Craft Advisory for hazardous seas until 4 AM EDT early this morning for ANZ254-255. && $$ SYNOPSIS...Nocera/Dunten NEAR TERM...EVT SHORT TERM...Nocera LONG TERM...Dunten AVIATION...Dunten/EVT MARINE...Nocera/Dunten/EVT FIRE WEATHER...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.