Area Forecast Discussion
Issued by NWS Boston, MA

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251 FXUS61 KBOX 250544 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 144 AM EDT Tue Jul 25 2017 .SYNOPSIS... Cool and damp conditions will linger into Tuesday. High pressure will bring a return to dry and pleasant weather for Wednesday. Cold front with a surface low pressure wave approaches southern New England Thursday night and exits the area late Friday. Dry weather and seasonable temperatures expected next weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 10 PM Update... Nose of the NE low level jet combined with abundant low level moisture producing areas of drizzle across eastern MA. Hi-res guidance suggests at least patchy drizzle will persist into the overnight hours. Otherwise, lots of low clouds expected and a few showers from leftover complex in NY may spill into western MA/CT. Clouds will prevent much diurnal cooling with temps nearly steady. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... A little better start to Tuesday. Despite clouds lingering to start the day, we should see a drying and clearing trend during the afternoon, and especially Tuesday night, as a high pressure arrives from the north. With winds expected to be more from the north than east, max temperatures should be noticeably higher during the day than Monday, but still below normal. Below normal temperatures continue Tuesday night. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * Dry weather and seasonable temperatures on Wednesday * Showers and possible thunderstorms late Thu with showers likely lingering into Fri * Dry weather and seasonable temperatures likely for the weekend Overview... Ridge builds over the intermountain west while the eastern United States looks susceptible to troughing. An anomalously strong short wave trough for this time of year will cross the Great Lakes region on Thu and New England on Fri. There is considerable disagreement between the GFS and ECMWF operational runs and ensemble output regarding strength of this short wave trough. Dry weather should follow in the NW flow behind the short wave passage for the weekend when there is much better consensus among the medium range models. There is also fairly reasonable model consensus on 850 mb temperatures for the weekend time period with resultant surface temperatures likely near seasonable levels. With a few tweaks in the Thu and Fri period, have gone close to a model consensus for the longer term forecast period. Period of Focus...Thursday afternoon into Friday The one period of extra focus in the longer term period covers Thursday afternoon through Friday when operational and ensemble model disparities result in somewhat below average confidence on the outcome. All models depict the short wave trough passage but vary considerably in strength and some in timing. The ECMWF suite of model runs depict a much stronger and as one might expect slower system than the GFS suite of model runs. Timing could also play a role in convective potential on the front end late Thursday afternoon and evening. Have opted to go close to continuity with POPs and just a tad below model consensus due to model discrepancies. Nevertheless, do believe there will be enough energy to support likely POPs in most areas. Also, adjusted temperatures down just a little across northern MA from a straight model consensus due to a high probability of cloudiness and at least scattered showers. If the latest ECMWF run proves to be correct, then we will probably need to lower those high temperatures on Friday at least a little more and raise POPs. As the short wave trough approaches and the 500 mb heights begin to fall, the air mass becomes marginally unstable late Thursday, mainly across western and northern MA and do have a chance of thunder in the gridded forecast. The slower timing scenarios, however, would bring the forcing into the region well past the favorable diurnal time. There is relatively strong vertical shear as one might expect to be associated with a robust short wave trough, but the degree of instability remains something of a question mark. For now, have high chance or low likely showers and slight chance or chance thunder. We`ll be able to refine this as we get closer. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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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 Wednesday/... Through 12z...Widespread MVFR/IFR cigs along with patchy fog. Patchy drizzle across eastern MA with a few showers moving across western/central MA. Today...Moderate confidence. MVFR cigs slowly lifting and possibly becoming VFR by late in the day. Low risk of a brief shower. Tonight...High confidence. VFR with clearing skies overnight. Wednesday...High confidence. VFR. KBOS Terminal...Moderate confidence. MVFR/IFR cigs improving to MVFR during the morning and lifting to VFR by late in the day. KBDL Terminal...Moderate confidence. MVFR cigs lifting to VFR by late in the day. Outlook /Wednesday Night through Saturday/... Wednesday night through Thursday morning...VFR. Late Thursday afternoon through Friday...MVFR ceilings and visibilities in areas of showers. Isolated thunderstorms late Thursday afternoon and evening. Saturday...VFR.
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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 Wednesday/... Low pressure moves farther away from the waters tonight, backing winds from northeast to north across most of the waters. Reduced visibility in rain and fog. rain diminishes this evening, but fog and spotty drizzle likely to linger through daybreak Tuesday. Small Craft Advisory for most waters continues, concluding late Tuesday into Tuesday night as winds subside and seas diminish. Outlook /Wednesday Night through Saturday/... Conditions during most of the period will likely remain below Small Craft Advisory thresholds. However, this is a risk that winds and seas may approach 25 knots and 5 feet, respectively, in an increasing SW flow Thursday afternoon and a northerly flow Friday afternoon and night, depending upon the strength of a low pressure area that passes across New England and the Gulf of Maine on Friday.
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&& .TIDES/COASTAL FLOODING... Continued strong NE flow continues tonight with sustained winds around 10 to 15 mph with gusts upwards of 30 mph. This yields a surge upwards of a foot for locations along the E MA coast N of a low sweeping W to E along the waters south of New England. A Coastal Flood Advisory continues for the evening high tide accordingly, given surge on top of high astronomical high tides. && .CLIMATE... Here is where we stand for record low maximum temperatures for the calendar day. Record Max Temperature Boston 63 - 1904 65 Hartford 67 - 1997 68 Providence 67 - 1997 66 * probable new record Worcester 60 - 1964 61 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Coastal Flood Advisory until 3 AM EDT early this morning for MAZ007-015-016-019-022-024. RI...None. MARINE...Small Craft Advisory until 2 AM EDT early this morning for ANZ230. Small Craft Advisory until 2 PM EDT this afternoon for ANZ231- 251. Small Craft Advisory until 9 AM EDT this morning for ANZ235- 237. Small Craft Advisory until 8 PM EDT this evening for ANZ250. Small Craft Advisory until 3 AM EDT Wednesday for ANZ254. Small Craft Advisory until 2 AM EDT Wednesday for ANZ255-256.
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&& $$ SYNOPSIS...Belk/Thompson NEAR TERM...KJC SHORT TERM...Belk LONG TERM...Thompson AVIATION...KJC/Thompson MARINE...Belk/Thompson TIDES/COASTAL FLOODING... CLIMATE...

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