Area Forecast Discussion
Issued by NWS Boston, MA

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418 FXUS61 KBOX 230833 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 433 AM EDT THU JUN 23 2016 .SYNOPSIS... Low pressure tracking south of New England may bring a few showers today, mainly along the south coast and islands. Large high pressure will build across the region Friday and Saturday, then shift east into early next week. This brings a spell of dry and warming weather through Monday. An approaching cold front may bring showers and thunderstorms Tuesday and Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Patchy low clouds and fog were lingering close to the coast of outer Cape Cod and Nantucket early this morning, with visibilities briefly lowering to below one mile. Those clouds have moved offshore on light southwest winds at 07Z. Otherwise, skies were mainly clear except for some patchy mid level clouds that have been pushing across the region in the west to northwest flow that is in place aloft. With light west to southwest or calm winds across the region at 08Z, there is quite a range of temperatures. In the normally cooler valley locations, readings have fallen to the mid 40s, with the mildest temperatures along the south coast, Cape Cod and the islands in the lower-mid 60s with light southwest winds. With those temperatures falling close to the dewpoints across inland areas, will see patchy fog develop through daybreak. Already noting visibilities down to 3/4 mile at KOWD and 4 miles at KTAN at 08Z. Overall upper level pattern across the northeast U.S. continues to keep long wave troughing and a general W-NW steering current in place. This will keep low pressure working out of the eastern Ohio valley S of the region today, moving along a stalled front draped from southern PA to central NJ extending offshore well S of New England. The strong convection associated with this low will push across the mid Atlantic states and off the coast. However, the northern fringe of the precipitation shield may sneak in close enough to bring widely scattered showers across south coastal areas during the day. Some marginal instability, with K indices around 30 and LIs around zero, may try to sneak into the coastal waters and the islands late in the day. Elsewhere, expect partly to mostly sunny skies with the best conditions across northern Mass where the most sun will appear. Expect temps to rebound to the lower-mid 70s along the S coast ranging to around 80 across N Mass as well as portions of the CT valley. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight... As low pressure pushes offshore well S of the region, expect any lingering showers, and even the low chance for a brief thunderstorm over the coastal waters this evening, to push offshore as well. Clouds will exit from NW-SE tonight with drier air moving in. May see some brief patchy fog develop near Nantucket again off and on tonight as the drier air will take its time moving in there. Expect winds to become light N-NW tonight, stirring just enough to prevent radiational cooling. Lows will generally be in the 50s, coolest across the higher inland terrain of N central and NW Mass., but may hold around 60 along the immediate S coast and on the islands. Friday... Large high pressure will begin to build SE out of south central Canada and the Great Lakes region on the continued W-NW flow aloft. Will see abundant sunshine with good subsidence in place. Expect seasonable temperatures, ranging from the mid 70s along the immediate coast to the lower-mid 80s, mildest across the lower CT valley. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Big Picture... Longwave scale shows a persistent trough in Eastern North America and ridge over the West. Shortwave scale shows a ridge building over New England Saturday and Sunday before diminishing late Monday. A shortwave originating over the Pacific Northwest moves east across Canada over the weekend and then digs over New England Tuesday and Wednesday. The building ridge and increasing contour heights suggest a warming trend over the weekend. Forecast contour heights are about 120 meters above normal by Sunday. As the shortwave approaches Tuesday- Wednesday the heights fall and values return to near normal. Model forecast mass fields are similar through Monday, then diverge a little early next week. Even with the divergence, the forecast scenarios are similar. This encourages confidence in the forecast through early next week. Details... Friday night through Monday...High confidence. Surface high pressure over the region Friday night and Saturday shifts east by Sunday and Monday. The surface high combined with building heights aloft will lead to fair weather and a warming trend through Monday. A light low level east flow Saturday trends to a south to southwest flow Sunday and Monday. The mixed layer is forecast to reach above 850 mb, and may approach 800 mb each day. This brings 850-equivalent temps of 13-16C Saturday and 16-18C Sunday and Monday...with surface max temps in the mid and upper 80s Saturday and upper 80s/lower 90s Sunday and Monday. These temps may be buffered by flow off the cooler ocean in RI and Eastern Mass, especially Saturday. Monday night through Wednesday...Moderate confidence. Upper shortwave approaches, driving a surface cold front toward New England. Models show some difference in timing with the ECMWF now faster than the other models in bringing pcpn into Western New England later Monday. The rest hold off until Monday night, timing that we favor. There are also timing differences in the cold front passage with the ECMWF sooner/GFS later. We will feature chance pops all areas Tuesday and Wednesday and await resolution of the timing differences. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Today...Moderate to high confidence. Mainly VFR CIGS. May see brief MVFR VSBYS along the S coast in widely scattered showers, mainly from late morning through the afternoon. Patchy early morning fog with local MVFR- IFR VSBYS in the normally susceptible locations of interior E Mass and N central areas through 13Z-14Z. Tonight...High confidence. VFR. Low chance for MVFR-IFR VSBYS in patchy fog INVOF KACK and the outer Cape around or after 03Z, that should improve by daybreak. Friday...High confidence. VFR. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Friday Night through Monday/... High confidence. Areas of IFR and LIFR in late night/early morning fog. Otherwise VFR. Sea Breezes expected Saturday. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Today...Leftover seas up to 5 ft on the southern outer waters should subside by mid morning. Some visibility restrictions possible across the southern waters in patchy fog through mid-late morning, then in widely scattered showers. Tonight and Friday...Winds and seas will remain below small craft criteria. May see some leftover visibility restrictions in patchy fog and any lingering showers tonight across the southern waters mainly from E of Cape Cod to S of Nantucket and Martha`s Vineyard. Should improve toward daybreak Friday. Outlook /Friday Night through Monday/...Moderate confidence. Winds remain below 25 knots and seas below 5 feet through the period. The southern waters may experience a 4 foot swell Saturday and a 3 to 4 foot swell Sunday. Coastal sea breezes possible Saturday all coasts and Sunday-Monday south coast. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 8 AM EDT this morning for ANZ254>256. && $$ SYNOPSIS...WTB/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.