Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 241201 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 801 AM EDT WED AUG 24 2016 .SYNOPSIS... High pressure will remain in control with higher temperatures today, but continued low humidity. More warm, humid conditions will return late this week. There is a risk for showers and thunderstorms Thursday night and Friday as a weak front passes. Another high will bring dry and somewhat less humid weather this weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 745 AM Update... Other than some patchy fog across portions of the CT valley and Berkshires, which was starting to improve at 11Z, skies were mainly clear across the region except for some patchy high clouds. Noting some valley fog on latest visible satellite /1145Z/ across the mid and upper CT valley. With high pressure in place just off the NJ coast and ridging across the region, expect clear skies to continue through the day. Near term forecast pretty much on target except for temps/dewpts being a bit lower than forecast prior to sunrise. Have updated to bring conditions current. Remainder of forecast on target. Previous Discussion... Still expecting a high pressure to move farther offshore while remaining to our south. This will mean a more dominant southwest flow, leading to slightly higher temperatures later on. Humidity levels will remain low as mixing of dry boundary layer keeps dewpoints down into the 50s for most. The big question will be the formation of an east coast seabreeze. Boundary layer winds should remain less than 10 kt, which is a sign the seabreeze could form. Seeing hints at it is some of the high resolution guidance. Based on the expected pattern, with high pressure moving farther offshore, thinking a weak east coast sea breeze will form, but it will start later than usual. With synoptic southwest onshore flow, expecting lower temperatures along the immediate south coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... High pressure continues to move farther offshore. South to southwest winds continue to increase ever so slightly through this period. Expecting near to above normal temperatures through Thursday. Latest guidance continues to show the slow approach of a prefrontal trough toward western New England late Thursday. Given weak forcing, and relatively lower humidity, decided to keep the forecast dry through Thursday. There is a possibility for a few isolated showers across western MA, but not enough of a risk to put showers in the forecast at this time. This timing may change. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Scattered showers/thunderstorms Thursday night and Friday * Drier weather this weekend * Another front may bring shot of wet weather Sunday night and Monday Overview and model preferences... Overall summer pattern remains in place across North America during most if not all of this timeframe as high pressure remains across the south central and SE U.S., keeping a rather fast mid level W-SW wind flow in place late this week across the northern tier states. Noting the overall H5 pattern begins to shift S Thu night/Fri as a surface front works SE out of central Ontario/Quebec. This will push off the south coast of New England by early this weekend, with high pressure bringing more dry and somewhat less humid conditions. 00Z operational models are in lower agreement in bringing an H5 short wave and its associated weak low pressure/front in the fast flow aloft, with the ECMWF a bit more bullish with its precip field vs. the GGEM and GFS for Sunday night and Monday. Less confidence with the timing of this feature. Have lower confidence with evolution of the upper level pattern early next week. Big questions as to the development and track of a tropical wave /99L/ near or east of the Bahamas. At this point, does not appear to affect the region, but may influence the overall upper level pattern, potentially somewhere across the southern Gulf states, but could be further into next week before any possible effects are felt. Details... Thursday night-Friday...High pressure remains along the eastern seaboard with SW wind flow in place. H5 heights lower somewhat, with surface low pressure and associated cold front moving slowly across during this timeframe. PWATs increase to 1.8 to 1.9 inches, so should see some rainfall with this front. However, noting rather limited instability but best near and with the passing front. Have mentioned scattered showers/thunderstorms in the forecast, with best shot across central and northern areas Thu night through midday Friday. Will remain warm/humid Thu night with lows only in the mid 60s to around 70. As the front passes, winds will shift to W-NW during the day Friday. However, somewhat drier air will be delayed until Friday night so will still feel rather humid. Highs will be in the mid-upper 80s. Saturday-Sunday...Large high pressure will cross the northeast U.S. with somewhat cooler and drier conditions. Dewpts will only fall back to the lower-mid 60s, with some upper 50s Saturday night across the inland valleys. N-NW wind to start off Saturday, then will veer to E-NE during later Saturday and E-SE on Sunday. With the warm sea surface temps on place, not much cooling air off the ocean. Expect highs both days in the lower-mid 80s, except in the mid- upper 70s along the immediate S coast. Another front may begin to approach Sunday night, which push a few widely scattered showers around the Route 2 area of N Mass. However, timing is in question with the large high across the mid Atlantic/SE U.S. states. Monday-Tuesday...Low confidence on timing of the approaching front during Monday, which is somewhat faster on the GFS vs. the ECMWF. Went along with ensemble guidance for this timeframe, with chance POPs going for most of Monday into Monday night. Still quite a few questions on Tuesday, as the front may stall near or just off the southern New England coast. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High Confidence. Mainly VFR. Increasing mid and high clouds Thursday. Low risk for patchy IFR/MVFR in fog later tonight/early Thu morning at the most fog prone locations. KBOS Terminal...Moderate confidence in the TAF. Some of the latest guidance develops a late sea breeze based on the expected light winds within the lowest 2 kft. It is possible southwest winds dominate, which may keep the sea breeze just east of the terminal. KBDL Terminal...High confidence in the TAF. Outlook /Thursday Night through Sunday/... Thursday night...Moderate to high Confidence. Mainly VFR. S-SW winds gusting to 20 kt along the S coast Thu evening. Scattered showers/isolated thunderstorms push into N and W areas overnight along with patchy late night fog in normally prone valley locations. Local MVFR-IFR conditions. Friday...Moderate Confidence. Scattered SHRA/TSRA as cold front moves across the region. Mainly VFR with local TEMPO MVFR-IFR CIGS/VSBYS possible with any storms. Conditions improve from NW-SE Friday night, though may see brief patchy fog across portions of CT valley after 07Z-08Z. Saturday and Sunday...High Confidence. VFR. Light winds. Likely sea breezes on Saturday. Winds becoming E-SE Sunday. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Tranquil boating conditions through the period as high pressure remains in control of our weather.. Mainly SW winds 15 kt or less with light seas and good visibility. A few gusts up to 20 kt possible Thursday, especially during the afternoon. Outlook /Thursday Night through Sunday/... Thursday night...High Confidence. S-SW winds gusting to around 20 kt Thursday evening along the southern near shore waters. May see local MVFR-IFR VSBYs in patchy fog mainly after 06Z along the southern near shore waters. Seas may briefly reach 5 ft on the outer waters east of Cape Ann early. Friday...Moderate Confidence. S-SW winds gusting up to 25 kt on the southern waters to east of Cape Cod with seas building to around 5 ft. Winds will diminish as they shift to W-NW Friday night. Seas subside below 5 ft. Patchy fog may develop overnight on the southern outer waters. Saturday and Sunday...High Confidence. Expect N winds shifting to E-NE during Saturday, then E-SE on Sunday. Winds and seas remain below small craft criteria. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/EVT NEAR TERM...Belk/EVT SHORT TERM...Belk LONG TERM...EVT AVIATION...Belk/EVT MARINE...Belk/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.