Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250805 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 405 AM EDT WED MAY 25 2016 .SYNOPSIS...
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An upper level ridge of high pressure will bring very warm to borderline hot weather to most of the region Today through Saturday, except for cooler temperatures at times along the immediate coast. A backdoor cold front will bring cooler weather to the region sometime on Sunday, but temperatures should rebound to at or above normal by early next week. A few showers and thunderstorms are possible Thursday night into Friday, and again this weekend but the vast majority of this time will be dry.
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&& .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/...
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Highlights... * Friday: Very warm w/highs mid-upper 80s northwest of Bos-Pvd but a bit cooler across Southeast MA/RI * Saturday: Hot and a bit humid w/highs mainly upper 80s to lower 90s away from the immediate south coast * Sunday: Temps uncertain depending on timing of cold front, warmest readings likely CT River Valley w/coolest across Eastern MA coast * A few showers/t-storms possible Thu night/Fri and again Sat/Sun but the vast majority of this time will be dry * At or above normal temperatures likely return early next week Details... Thursday night...Shortwave energy and a burst of elevated instability may result in a few showers/t-storms Thursday night, mainly northwest of a Boston to Providence line. If any activity is able to develop it will be short-lived with the majority of the night ending up dry. Low temps mainly in the upper 50s to the lower 60s. May see some patchy ground fog develop late in the typically prone locations. Friday...Surface winds shift to the south southwest behind the warm front as 850T rise to around +14C. Plenty of sunshine should allow highs to warm into the middle to upper 80s northwest of a Boston to Providence line. Southeast of this line...a cooling marine layer may hold highs in the upper 70s to the lower 80s. Dry weather will dominate on Friday...but enough instability combined with a pre-frontal trough may allow a few showers/thunderstorms to develop across Western MA/Northern CT Fri afternoon and evening. Not sure if this activity gets into our region or stays to our west...but highest risk will be across northwest MA. Shear is rather weak so even if we see a few thunderstorms in our western zones...overall severe weather threat is rather low. Saturday...A hot and somewhat humid day is on tap to kick of the Memorial Day Weekend. 850T around +16C, plenty of sunshine, and a westerly component to the surface winds should allow for high temps to reach into the upper 80s to the lower 90s away from the immediate south coast. Dewpoints between 60 and 65 across most of the region will make it feel a bit humid. While most of the day will be dry...a few showers and thunderstorms may develop Saturday afternoon and evening with a pre-frontal trough and Cape values between 1000 and 2000 J/KG. This will be mainly to the northwest of a Boston to Providence line. Forcing will be rather weak, so areal coverage of any activity that develops may remain limited. Severe weather threat also looks rather low at this time with rather weak 0 to 6 km shear...but too early to rule out a strong thunderstorm or two given decent instability. Sunday...Low confidence on high temperatures given a subtle change in timing of the backdoor cold front will make a big difference in the exact outcome. We can say that the warmest readings will be across the Lower CT River Vally and coolest along the Eastern MA coast. Good shot though at the CT River Valley seeing high temps reach well into the 80s...while the Eastern MA coast has afternoon temps falling into the 60s. A few showers will remain possible and perhaps even a couple of t-storms across the interior if enough instability develops during the afternoon. Monday and Tuesday...Backdoor cold front does not appear as strong on the latest model runs. It looks to washout across the region early next week. GFS washes out on Monday while the ECMWF waits until Tuesday. Probably should see the return to above normal temps by Tue with rather warm temps aloft.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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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 to high confidence. VFR conditions likely dominate but some brief MVFR conditions possible in a few brief showers/t-storms mainly across the interior. Also, some patchy ground fog possible in the typically prone locations very early Fri am. Saturday...Moderate to high confidence. VFR conditions likely dominate but a brief period of MVFR-IFR Cigs/Vsbys possible in a few afternoon and evening showers/thunderstorms. Sunday...Low confidence. MVFR-IFR conditions may develop from east to west behind a backdoor cold front. A few thunderstorms also possible Sun afternoon across the interior.
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&& .MARINE...
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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 generally remain below Small Craft Advisory thresholds through the period. The main concerns are a period of near shore southwest wind gusts of 20 to 25 knots Saturday afternoon which will result in some choppy seas for mariners. May also see some brief easterly wind gusts between 20 and 25 knots on Sunday behind a backdoor cold front.
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&& .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...
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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...None.
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&& $$ SYNOPSIS...Frank NEAR TERM...EVT SHORT TERM...Nocera LONG TERM...Frank AVIATION...Dunten/EVT/Frank MARINE...Dunten/EVT/Frank FIRE WEATHER...Staff

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