Area Forecast Discussion
Issued by NWS Boston, MA

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191 FXUS61 KBOX 270855 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 455 AM EDT MON JUN 27 2016 .SYNOPSIS... High pressure remains in control today into Tuesday. A cool front will slowly approach the region, bringing showers and thunderstorms late Tuesday through Wednesday. The front will push offshore Wednesday night. High pressure then brings dry seasonable weather for the late week. Another cold front may bring more showers and thunderstorms around Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Skies remain mainly clear early this morning except for some thin patches of cirrus clouds crossing the area. Some patchy mid level clouds trying to shift E-SE out of upstate NY as seen on latest IR satellite imagery, but are tending to dissipate are they reach the New England/NY border with very dry airmass aloft, as well as ridging at the surface and aloft. As H5 heights tend to lower during the day, the upper ridge will recede southwestward as weak mid level trough sits over the Gulf of Maine and E of Cape Cod. H5 short wave begins to dig across the Great Lakes during the day. Lead pre-frontal trough heads out ahead of the main short wave, so will see a line of showers/tstms push across NY state during the day. Short range models continue to suggest that some may begin to reach into the E slopes of the Berkshires late in the day. Only mentioned slight chance POPs there. Will see dry conditions for most areas through the day, though clouds will increase across western areas this afternoon. With the general S-SW winds in place, expect temps to top off in the lower-mid 80s, except only in the 70s along the S coast with the onshore winds. Will see a gradual increase in humidities during the day, with dewpts reaching to around 60 along the S coast by evening. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight... As pre-frontal trough slowly pushes eastward, it will weaken tonight. However, could see enough forcing and dynamics work into central and western areas to keep some scattered showers and even an isold thunderstorm or two to move in. Noting as band of increasing PWATs associated with this trough, on order of 1.6 to 1.8 inches with it. Dewpts will also continue to slowly increase as well, so patchy fog could also develop with the precipitation as well as along the S coast with the onshore winds. Expect temps to fall back to the lower-mid 60s. Tuesday... H5 short wave works slowly eastward to W NY state Tuesday afternoon/evening. Leftover instability with the weakening pre- frontal trough becomes parallel to the SW upper flow ahead of the short wave. Also, convection with the main front, which will cross into eastern NY state during the afternoon, will refire and push into central and western areas. Have carried mainly chance POPs for most areas away from the coastal plain, with best shot from the CT valley to the E slopes of the Berkshires. Will probably see little if any precip through Tuesday across Cape Cod and the islands. Expect muggy conditions /dewpts in the lower-mid 60s/ with highs running mainly in the mid 70s to around 80, though a bit cooler on the outer Cape and islands. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Big Picture... Longwave scale continues to show a ridge-west/trough-east pattern over North America. This may shift east a little during the holiday weekend. One shortwave rippling through this flow moves across New England later Wednesday. A second moves down from Canada and sweeps across New England next weekend. Model mass fields are similar with the broad pattern through Friday. There are differences in positioning of the cold front associated with the first shortwave. The ECMWF is farthest west and the GGEM farthest east. This means a consensus as to the broader forecast, showers/tstms, but uncertainty regarding the details such as timing. With the second shortwave, the GFS and ECMWF are similar while the GGEM is slower and farther south. The mass field agreement and the variations in details Tuesday night/Wednesday favor a blend of model data. Details... Tuesday night through Wednesday... Shortwave over the Eastern Great Lakes digs over New England while the associated surface cold front moves through Eastern New York Tuesday night and New England Wednesday. The upper flow through the shortwave will be SSW to NNE across our area, almost parallel to the cold front. Until the shortwave axis swings across our area and turns the upper flow across the front, the cold front will move very slowly. Upper jet flowing through the shortwave will provide dynamic support for lift. Model data shows precipitable water values pooling along and just ahead of the front with max values 1.6 to 1.8 inches. Three of four models show total-totals in the upper 40s Tuesday night through Wednesday afternoon in the area leading the cold front. Cross sections show the moisture will be through a deep column. All of this points to showers and possible thunderstorms. We will stay with likely pops Tuesday night and chance pops Wednesday. Thursday through Saturday... Weak high pressure builds over the region Thursday and lingers into Friday. The second shortwave approaches with difluent flow aloft Friday afternoon/evening and increasing precip water values toward evening. Favorable instability remains to our west and northwest during Friday but then moves across Southern New England Friday night. Timing on this shortwave and surface cold front will continue to vary, but for now we will show chance pops for showers/tstms in extreme western MA Friday afternoon and chance pops for most of the area Friday night. Showers/thunder end from west to east Saturday morning. Temps aloft 13-15C should support max sfc temps in the low to mid 80s. Sunday... The Saturday cold front moves south of New England, but with long range data suggesting it may stall to our south. In this scenario, a low pressure wave would move along the front from the Ohio Valley and pass south of us. There is some potential for clouds and a chance of showers for July 3rd, mostly along our South Coast with diminishing likelihood to the north. This will need to be monitored. && .AVIATION /09Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Through 12Z...High Confidence. VFR. Brief local IFR-LIFR conditions in patchy ground fog and/or low clouds in normally prone valley areas. Today...High Confidence. VFR. Any IFR-LIFR fog/CIGS dissipate by 13Z. Expect S-SW winds gradually increasing, gusts up to 20-25 kt during the afternoon. Tonight...Moderate Confidence. Mainly VFR. Scattered showers/isold TSRA move into central and western areas mainly near or after midnight with MVFR-IFR CIGS/VSBYS. Low chance for LIFR CIGS in stratus/fog across S coastal areas. Tuesday...Moderate confidence. Low clouds and fog with patchy MVFR- IFR conditions through 14Z along the S coast. Will see MVFR-IFR conditions in scattered SHRA/TSRA, mainly from away from the coastal plain through the day. KBOS TAF...High confidence. VFR. S winds increase today, gusting up to around 20 kts during the afternoon hours. KBDL TAF...High confidence. VFR. Low to moderate chance for MVFR- IFR CIGS/VSBYS late tonight in low clouds/fog. Outlook /Tuesday Night through Friday/... Tuesday night-Wednesday... Moderate confidence VFR with areas of MVFR in showers and thunderstorms Tuesday night and Wednesday morning. Areas of IFR possible in fog and low clouds. South winds gusting to 20 knots will shift from the West after the cold front moves through Wednesday. Thursday-Friday...Moderate confidence VFR. North winds become variable Thursday, then from the south Friday. Showers/tstms will develop over New York State, and may move into Southern New England Friday evening and night. These showers and storms would have areas of MVFR cigs/vsbys. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Today...High confidence. Expect south winds to increase this afternoon. Gusts will reach to around 25 kt on the eastern outer waters from N of Cape Cod to Cape Ann. Seas also build to around 5 ft there. Small craft advisory in effect. Elsewhere, will see gusts up to 20 kt with seas 4 ft or less. Tonight...Moderate confidence. Small crafts will continue for the waters from N of Cape Cod to Cape Ann, though winds and seas should diminish after midnight. Otherwise, winds and seas below small craft. Reduced visibilities around or after midnight in patchy fog, mainly over the open waters. Widely scattered showers/thunderstorms toward daybreak off Cape Ann, and scattered showers from Block Island westward. Tuesday...Moderate confidence. South winds continue, with some gusts up to 20 kt on the eastern outer waters. Seas 4 ft or less. Reduced visibilities in patchy morning fog. Chance for showers/thunderstorms mainly on the near shore waters. Outlook /Tuesday Night through Friday/... Tuesday night-Wednesday...Moderate confidence. Showers and thunderstorms cross the waters with south wind gusts near 20 knots at times. Winds shift from the west Wednesday as a cold front crosses the waters. Low vsbys possible ahead of the cold front in showers and storms as well as in fog. No headlines planned at this time. Thursday-Friday...Moderate confidence. High pressure builds over the waters Thursday and moves off to the east Friday. A cold front approaches from the west Friday night. Winds and seas should remain below Small Craft Advisory criteria. Scattered showers/thunderstorms possible Friday night as the cold front approaches. && .FIRE WEATHER... With the long term dry conditions across the region over the last few weeks and beyond, expect another dry and breezy day today. Will see south-southwest winds pick up mainly this afternoon, with gusts up to 25-30 mph. Expect the highest winds gusts across eastern Massachusetts as well as the Connecticut River valley. Minimum relative humidities will drop off to between 30 and 40 percent from northern Connecticut, northern Rhode Island into interior southeast Massachusetts northward from late morning into late this afternoon. Will continue to monitor the fire weather conditions through this afternoon. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 1 PM this afternoon to 2 AM EDT Tuesday for ANZ250. && $$ SYNOPSIS...WTB/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT

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