Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 230743 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 343 AM EDT THU JUN 23 2016 .SYNOPSIS...
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Low pressure tracking south of New England may bring a few showers Thursday, mainly along the south coast and islands. High pressure over the region Friday and Saturday shifts east over the ocean during the weekend. This brings a spell of dry and warming weather through early next week. An approaching cold front may bring showers and thunderstorms Tuesday and Wednesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1030 PM Update... Bands of mid and high clouds crossing the region as seen on latest IR satellite imagery, which should push offshore by 04Z- 05Z. Otherwise, expect dry conditions with cooling temperatures. Already noting readings in the mid-upper 50s across the interior E Mass valleys as well as portions of the CT valley at 02Z. With the dropping dewpoints across the region, continued to keep low stratus and fog out of the forecast based on current conditions and previous forecast. Winds will drop off to light/variable or calm as weak ridge builds across overnight. Have updated near term forecast to bring conditions current. Previous discussion... Overall trend in the forecast for tonight remains on track. weak boundary/cold front has pushed through the entire area removing all chance for stratus and fog for the Cape and the Islands. Dewpoints continue to drop into the 50s for that area. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Previous Update... Made changes to the Thursday forecast for the 7PM update. The 18z NAM and GFS continue to trend towards the EC and RGEM to show a shut out for southern New England for precip. There may be a spot shower or two, but the precip chances continue to decrease. Have reflected this within the forecast. It may even be that ACK could be the only site to see any precip as MCS will rob the moisture for any showers to develop. Will have to continue to watch MCS development and how it propagates overnight. Thursday... Surface low pres moves along boundary and tracks south of New England. The morning will start out dry with some sunshine but deeper moisture and weak lift north of the low may bring a period of showers to the region, especially near the south coast. There is uncertainty with how far north deeper moisture gets. ECMWF and RGEM are south and a shutout for SNE while NAM/GFS and UKMET bring rain to SNE, mainly south of the Pike. One factor which may complicate how far N moisture gets is a potential MCS which is forecast to track across mid atlc region. This could cut off moisture transport into SNE. We will go with just chc pops along and south of the Mass Pike with likely over the islands. Confidence is below normal and it is possible rain remains mostly south of New Eng. Some uncertainty with temps which will be dependent on sensible weather. Highs should be mainly in the 70s, possibly near 80 near the NH border, but if rain remains to the south will likely see temps reach into the 80s. Thursday night... Low pres moves offshore as high pres builds to the north. Clearing skies and light winds will result in another cool night with lows in the 50s, with some upper 40s possible in colder spots in CT valley. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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Big Picture... Longwave scale shows a persistant 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.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Overnight...High Confidence. VFR. Very low prob for stratus on the islands and portions of outer Cape Cod and Nantucket. Thursday...Moderate confidence. Mainly VFR CIGS, though may see brief MVFR along the S coast in showers. Lower risk of showers further N. Thursday night...High confidence. VFR. KBOS TAF...High confidence. KBDL TAF...High confidence. Outlook /Friday night through Monday/... High confidence. Areas of IFR and LIFR in late night/early morning fog. Otherwise VFR. Sea Breezes expected Saturday.
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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. Short Term /through Friday/...High confidence. Winds will remain below SCA through Thu night. Light winds tonight become E-SE Thu, then north Thu night. Lingering 5 ft swell over the southern waters will gradually subside overnight into Thu morning. Showers possible over the southern waters Thu. 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.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 8 AM EDT this morning for ANZ254>256.
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&& $$ SYNOPSIS...WTB/KJC NEAR TERM...Dunten/EVT SHORT TERM...KJC/Dunten LONG TERM...WTB AVIATION...WTB/KJC/EVT MARINE...WTB/KJC/EVT

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