Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251608 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1208 PM EDT MON JUL 25 2016 .SYNOPSIS... Summer heat will continue into much of the upcoming week. A weak front will bring an increased risk of showers and thunderstorms... some possibly severe...this afternoon and evening. Showers and thunderstorms are possible again late next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1215 PM update... Have expanded the Heat Advisory to include northeast CT, far northern RI, and portions of interior eastern MA. Heat Index values will be near 100 in the CT River valley and in the 95-100 range in the remainder of the Advisory area. Convective update... Line of thunderstorms approaching the Hudson Valley in eastern NY has not weakened. It will be approaching surface based CAPE values of 1000-1500 and is not expected to weaken as it approaches western MA. These could become severe. The RAP and HRRR are not capturing this convection. Behind this line, abundant sunshine in southern NY may help a second, potentially more potent area form and move into our region late this afternoon. Previous discussion... Have issued a Special Weather Statement about the potential for severe thunderstorms across portions of southern New England this afternoon and evening. Skies have been mostly sunny this morning ahead of convection in New York state. Already temperatures have soared into the upper 80s away from the coast. At the coast, sea breezes have kept temperatures in the upper 70s and lower 80s so far. Dewpoints have risen to near 70 across northern CT, RI, and southeast MA, but remain in the upper 50s in northeast MA. These are expected to continue to rise through the 60s there. Regarding heat, we have forecast max temperatures in the mid 90s in the CT River valley and in the Merrimack Valley of MA for this afternoon, since the cloud debris from upstream convection has been slow to move into the area. Dewpoints are highest in the CT River Valley, where heat index values reach 100 degrees this afternoon and a Heat Advisory remains in effect. In the Merrimack Valley and other portions of interior eastern MA, the heat index may reach the mid to upper 90s, just shy of Heat Advisory criteria, but in the northeast, that is dependent on the dewpoints rising to the mid and upper 60s. Regarding severe potential, all models show a coherent area of 38-40 K Index readings moving from the Berkshires at 1 PM to Worcester County by 4 PM and at the coast around 7-8 PM. Am expecting the line of thunderstorms in New York to progress across southern New England at the time of maximum heating. With dry air aloft once again, we could see downburst potential in the stronger thunderstorms. We have put enhanced wording...possibly severe...into the forecast for areas with the highest CAPE values. SPC mesoanalysis shows a RAP forecast of an axis of higher Downdraft CAPEs in eastern CT and RI this afternoon, which could be where the strongest storms evolve. High Precipitable Water Values near 2 inches in CT, RI, and southeast MA mean that localized urban flooding is possible with any storms as well. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight... With increasing mid lvl lapse as the core of the upper shortwave moves across the region, it may lead to lingering convection into the earlier overnight hours. This correlates to ML CAPEs near 1000j/kg lingering along with an increase in shear, closer to 35 kt. Timing of shortwave will be key, but eastern areas could see the remnant of this convection linger through 02-04Z (10-midnight local). Otherwise, dwpts will be slow to decrease even as winds shift toward the W-NW. Expect some localized ground fog especially where rainfall is observed. Indications suggest Cape/Islands see a mix of marine fog/stratus. Min temps mainly in the 60s. Tomorrow... Even with nose of high pres, NW flow and some cooling aloft. Temps will still approach the low to mid 90s thanks to some downsloping and H85 temps starting near +18C. Clearing skies after any stratus and or remnant high clouds dissipate. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Hot temperatures continue through the middle of this week, away from the coast * Should be a little less humid Tuesday and Wednesday * Showers and thunderstorms are possible again late this week Overview... 25/00z guidance is in decent overall agreement through mid week, then more significant differences in the details start to emerge. This is a bit of change from previous runs. Will favor a consensus approach for this forecast. That should smooth over the more minor differences through mid week, as well as account for the greater uncertainty late this week into next weekend. Details... Tuesday Night and Wednesday...Drier weather with high pressure in control. Still hot, especially away from the coasts. Sea breezes are more likely Thursday and Friday...Uncertainty increases with this portion of the forecast. Temperatures will cool a few degrees Thursday as clouds increase and a cold front starts to move through southern New England. This front is expected to stall somewhere near our region on Friday. The presence of this front, and likely increase in clouds, should lower max temperatures Friday. Scattered showers and thunderstorms will be possible with this frontal passage, particularly on Thursday when more instability is expected. They may linger into Friday, but as mentioned above, that will largely depend on how far off the south coast the front pushes. Regardless, Friday is likely to be cloudy and cooler, though more humid than previous days. Saturday and Sunday...Lots of uncertainty remains with this portion of the forecast, leading to a low confidence forecast. Latest runs of the models now keep a frontal boundary nearby. Will mention a chance of showers, for now. && .AVIATION /16Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Through today...Moderate confidence. Mainly VFR through the afternoon. Between 19Z and 03Z, a risk for TSRA and SHRA is expected with some strong winds and heavy rainfall. Localized IFR conditions likely in any TSRA. Tonight...moderate confidence. Most thunderstorms/showers end between 02Z and 04Z with VFR developing initially then late night fog especially at typically prone airports. Stratus also possible along the Cape/Islands especially. Mix of IFR/MVFR conditions. Tomorrow...high confidence. Mainly VFR after early morning fog/stratus dissipates. Winds mainly NW with gusts 15-20 kt. KBOS TAF...Moderate confidence in TAF. Sea breeze in place. VFR but chances of strong thunderstorms late this afternoon and evening. KBDL TAF...Moderate confidence in TAF. Chance of strong thunderstorms this afternoon. Outlook /Tuesday Night through Friday/...Moderate to high confidence. Quiet boating weather is expected through this time. The exception will be Thursday into Friday. While winds and seas will remain below small craft advisory criteria, low clouds, fog, and periodic showers and thunderstorms should limit visibilities. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. Seas remain below SCA. Winds from the W-SW, then shift to the NW tomorrow with some gusts 15-20 kt. There is a risk for thunderstorms late this afternoon and evening. Outlook /Tuesday Night through Friday/...Moderate to high confidence. Quiet boating weather is expected through this time. The exception will be Thursday and Friday when winds and seas will remain below SCA criteria, but low clouds, fog, and periodic showers and thunderstorms will limit visibilities. && .CLIMATE... Here are the record high max and min temperatures for July 25: Boston - 96 (1882)/78 (2001) Hartford - 98 (2001)/75 (2001) Providence - 96 (2001)/75 (2001) Worcester - 93 (1941)/73 (2001) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 6 PM EDT this evening for CTZ002>004. Air Quality Alert until 10 PM EDT this evening for CTZ002-003. MA...Air Quality Alert until 11 PM EDT this evening for MAZ004>016- 026. Heat Advisory until 6 PM EDT this evening for MAZ005-010>013- 017. RI...Heat Advisory until 6 PM EDT this evening for RIZ001. MARINE...None. && $$ SYNOPSIS...Belk/Doody/Field NEAR TERM...Field SHORT TERM...Doody LONG TERM...Belk AVIATION...Belk/Doody/Field MARINE...Belk/Doody/Field CLIMATE...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.