Area Forecast Discussion
Issued by NWS Boston, MA

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970 FXUS61 KBOX 240544 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 144 AM EDT Sun Sep 24 2017 .SYNOPSIS... High pressure, both at the surface and aloft, will extend from the eastern Great Lakes to New England overnight through early next week. It will bring unseasonably warm weather to the region into the middle of next week. Maria is expected to pass southeast of New England late in the week with strongest winds well offshore. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1130 pm update... Will be adding Dense Fog Advisory to Cape Cod and Islands including Block Island. Considered Plymouth County, but satellite trends show thinning of the stratus, so suspect the fog will thin shortly. Previous discussion... Fog over much of Eastern Massachusetts, with the GOES 16 fog product defining this area quite well. This same product shows some weakening of the stratus over the Gulf of Maine, but continued expansion over land and especially south of Boston. This fog should move into eastern RI in the next 1-2 hours. Also signs of potential development in the CT Valley and Quabbin area, as well as a few other spots, which would be expected under these conditions. Otherwise surface map shows high pressure over the Eastern USA with a light NNE flow over Southern New England. This will continue overnight and provide an environment favorable for fog expansion. Most observed visibilities are around 1/2 mile or higher, a little higher than we`d like to see for a Dense Fog Advisory. The exceptions toward the lower are Logan Airport and Marshfield which report 1/4 mile and less than 1/4 mile, respectively. We will hold off on a headline at this time but re-evaluate before midnight. Evening temperatures in the 60s and dew points in the mid 50s to mid 60s. With fair skies and light wind, expect a min temperature range in the mid 50s to lower 60s. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Tonight... Winds diminish tonight, which with clear skies will allow temperatures to cool to dew point. We trended toward the mos values for min temp, which was a couple of degrees lower than the standard guidance. Radiation fog possible in the interior, and marine fog/stratus is possible along the Cape/Islands/South Coast. Sunday... **RECORD HIGH TEMPERATURES EXPECTED** High pressure over the region, both at the surface and aloft, will mean sunshine and hot temperatures away from the coast. Heights at 500 mb are forecast at or above 590 Dm, and 850 temps are forecast at 18-20C. 925 mb temps are forecast to reach +24C. Expecting highs reaching the lower 90s in the CT River Valley, which would be a record...see Climate section at the end of this forecast discussion. Expecting upper 80s elsewhere in interior southern New England. Light winds under the high pressure will allow daytime sea breezes, which will keep temps much cooler along the shoreline....only 70s to near 80. The one big exception to the above will be Cape Cod and the islands, which are likely to begin the day with cloud cover and areas of fog, which may linger through a big chunk of the morning, before becoming partly sunny. Expecting highs on the Cape and islands to range from the upper 60s on Nantucket to the mid 70s on the upper Cape. With dewpoint temperatures only in the lower to mid 60s, the heat indices are forecast to reach 90 to 94, just shy of heat advisory criteria - although that criteria requires it to last for two days. Will need to keep an eye on this. Sunday night... Expecting mostly clear skies. Could see marine stratus again late at night over the Cape and islands. Patchy fog possible late in some interior areas. Lows in the 60s. Swells from Hurricane Maria will be reaching south coastal areas, so a High Surf Advisory remains posted for those areas. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Summer warmth expected to the middle of next week * Maria expected to sharply recurve out to sea southeast of New England late next week No major surprises in the 23/12Z guidance. Still expecting an anomalous mid level ridge to hover over our region through the middle of next week, although it should weaken with time after Tuesday. The strength of this ridge will be crucial in delaying the northward progress of Maria towards our region. High pressure with dry weather expected Monday and Tuesday. Temperatures should be 10-15 degrees above normal Monday, but not quite as much Tuesday or Wednesday. A few interior spots may reach 90 degrees Monday. Seabreezes should develop along both coasts, lowering daytime max temperatures there. A potential weak low level front just south of our region, may be enough to trigger a few showers Tuesday night into Wednesday. A greater risk for showers should be ahead of a cold front sweeping through our region Wednesday night into Thursday morning. This cold front and a potent mid level trough are expected to be the final kickers which steers Maria out to sea well to our south. Drier weather should prevail next Friday into Saturday, although cannot dismiss the possibility of some stray showers given the proximity of a mid level trough. The bigger change will be the temperatures, which should snap back to near normal levels during this time. The primary impact on our region from Maria will likely be another prolonged period of high surf and dangerous rip currents, mainly along ocean-exposed south coast beaches. For several days, Maria tracks near a great circle route in our direction and hence we will likely see significant long period swells from the S or SE propagate into our coastal waters most of next week. The slow northward speed of Maria for the next several days may enhance the swell activity during this period. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... Early morning...Moderate confidence, mainly due to timing. IFR/LIFR cigs/vsbys in fog in Southeast Mass and parts of RI. Satellite trends show signs of the fog shifting south toward the South Coast, but in general we expect the fog to linger overnight and then thin toward morning. Fog has not shown itself in the CT Valley despite a favorable environment for fog formation. We will continue to monitor and expect at least patchy fog toward morning. Today...High confidence. Any remaining fog will burn off in the morning. The last patches, likely on the Cape and Islands, should dissipate by 11 AM to Noon. VFR through the day with light wind inland and developing sea breezes late morning to early afternoon. Tonight...Moderate to high confidence. VFR most areas, however, could see marine IFR developing again on Cape Cod and the Islands. Patchy areas of fog may develop late over portions of the interior, such as the CT Valley. Monday... High confidence. Patches of IFR in fog to start the morning, but otherwise VFR through the day. Light wind, with sea breezes again developing. KBOS TAF...Moderate-high confidence. Patches of fog in all directions around the airport, but not at the field. Low to moderate chance of brief MVFR vsbys in fog early, but otherwise we expect VFR conditions through the day. Light wind will turn into an northeast sea breeze around 14Z, then a southeast seabreeze 18-19Z. The sea breeze should diminish 22-24Z. KBDL TAF...High confidence in TAF. Patchy MVFR vsbys in fog are possible early, but otherwise expect VFR through the forecast period with light wind. Outlook /Monday Night through Thursday/...Confidence...High. Monday night and Tuesday...VFR expected. Tuesday night...Mostly VFR except MVFR in patchy stratus/fog some interior valleys and near the south coast. Wednesday...Generally VFR except MVFR ceilings/visibilities possible in scattered late day showers and patchy late night/early morning stratus/fog. Thursday...Generally VFR, with MVFR in scattered showers during the morning. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...Moderate confidence. Leftover swell was diminishing along the east coast of MA. Low clouds and fog will continue along the southern and southeast coasts tonight with poor visibilities. Winds will diminish to less than 15 knots, but seas will linger at 5-6 feet on the southern outer waters. Sunday...Moderate confidence. High pressure building over the region will bring light wind, with sea breezes developing at the shoreline. Poor vsbys in fog early, slowly improving by late morning or early afternoon over the southeastern waters. Seas of 5-6 feet will linger on the southern outer waters. A south swell sent north from Maria will start showing itself in our southern waters late Sunday, with 3-4 feet swell heights in the afternoon. Sunday night...High confidence. Seas build to 5 to 7 feet over the southern outer waters, mainly due to swells from distant Hurricane Maria. High surf conditions will exist on area beaches along the south coast. Patchy areas of fog. Outlook /Monday Night through Thursday/...Confidence...High Relatively light winds are expected through this period. However, swells from Maria will propagate into the southern coastal waters, beginning late Sunday night or Monday. Small Craft Advisories will likely need to be extended due to rough seas for the waters south of the MA and RI coast for all of this period. The swells from Maria will likely produce another round of high surf and dangerous rip currents. && .TIDES/COASTAL FLOODING... High Surf Advisories will expired along the east coast of MA this evening, but they will remain in effect through Monday along the south coast. Swells from Maria will likely increase the surf and associated rip current risk across our ocean- exposed south coast starting late Sunday and continuing through the week. This will be true even though Maria may eventually recurves out to sea well southeast of New England. && .CLIMATE... Best chance for record high temps will be Sunday and Monday, when records are 85-90. Records jump up Tuesday to 89-95, while less mixing will lead to lower max temps. So the chance for new records diminishes Tuesday. The current record max temps for the three days are BOS 90/1959 89/1926 95/1881 ORH 85/2010 85/1970 91/1930 BDL 89/1959 90/2007 93/2007 PVD 87/1959 89/1920 89/2007 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 9 AM EDT this morning for MAZ022>024. High Surf Advisory until 6 PM EDT Monday for MAZ020-022>024. RI...Dense Fog Advisory until 9 AM EDT this morning for RIZ008. High Surf Advisory until 6 PM EDT Monday for RIZ006>008. MARINE...Small Craft Advisory from 2 AM to 6 PM EDT Monday for ANZ235- 237. Small Craft Advisory until 6 PM EDT Monday for ANZ254>256. && $$ SYNOPSIS...Belk/GAF NEAR TERM...WTB/Belk/GAF SHORT TERM...GAF LONG TERM...Belk AVIATION...WTB/Belk MARINE...WTB/Belk/GAF TIDES/COASTAL FLOODING... CLIMATE...

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