Area Forecast Discussion
Issued by NWS Boston, MA

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931 FXUS61 KBOX 250557 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 157 AM 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 Monday afternoon and evening and again late next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 10pm update... Forecast mainly on track. Convection riding best instability well to the SW. Even cloud debris not as widespread as initially thought. This may lead to better warming tomorrow, but this will need to be watched as new guidance comes in. Previous discussion... Quiet night tonight with just a few mid/high clouds expected. Weak shortwave triggering convective complex over Ohio valley will track to the mid atlc region toward 12z with any convective activity remaining to the SW of New Eng. Lows will be mainly in the 60s with increasing dewpoints after midnight. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/... *** Potential for strong to severe thunderstorms Mon afternoon and evening along with hot and very humid conditions *** Weak shortwave will be tracking south of New Eng in the morning with any convection likely remaining to the south. However, models indicate good influx of moisture as higher theta-e air moves into the region during the morning and this will be accompanied by some clouds and possibly even a few showers. These clouds may affect temps and instability but confidence in the extent of cloud cover is not high. We do expect at least partial sunshine and with 850 mb temps climbing to near 20C potential exists for a very hot day. If we had full sunshine potential for upper 90s to around 100 degrees but due to expectation of cloud cover we will not go quite this high, with high temps low to mid 90s away from the south coast. It will become rather humid with dewpoints climbing into the lower 70s. We will keep heat advisory for CT valley where heat indices expected to approach 100 degrees, but confidence not high enough to expand further east due to uncertainty in amount of sunshine. Other concern is the potential for severe weather Mon afternoon and evening as mid level trof/shortwave approaches from the Gt lakes. MLCAPES expected to peak around 1000-1500 J/kg during the afternoon. Initially, mid level lapse rates will not be ideal but pre-frontal trof will likely serve as a focus for developing convection and 0-6 km shear increasing to 35 kt which will result in an increased risk for severe weather. Severe threat likely to continue into the first half of Mon night as weakening remnant EML moves into the region. Mid level lapse rates increase to 6.5 C/km aided by subtle cooling aloft which will help to sustain convection as models indicate SBCAPES 500-1000 J/kg with deep layer shear above 30 kt during 00-06z. Damaging winds will be the primary threat of severe weather, especially with inverted V profile during the late afternoon. Heavy rainfall and localized flooding will be a secondary concern with PWATS increasing to near 2 inches. Front moves through overnight Mon night with notable drying in the column which will result in clearing skies and lower dewpoints moving into the region. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Hot temperatures continue through the middle of the week, away from the coast * Should be a little less humid Tuesday and Wednesday * Showers and thunderstorms are possible again late in the week Overview...Models are in fairly good agreement throughout the long term portion of the forecast. Minor timing differences as well as mesoscale differences show up, especially towards the end of the forecast period. Low pressure in the maritimes will bring the cold front through southern New England Tuesday, drying out the low levels. High pressure is the rule for Wednesday. Then Thursday and Friday, the ECMWF has a front with a series of low pressures along the front from the DelMarVa peninsula to the maritimes. The GFS is similar but less detailed with the areas of low pressure. This could bring periods of showers and possibly thunderstorms to southern New England. The front may push south of southern New England Friday with the low pressure over the DelMarVa peninsula traveling along the front south of the area. Question for Thursday and Friday is how far south the front pushes, as a move too far south may shut us out from any rain. High pressure starts to build back in again on Saturday and possibly on Sunday, though low pressure south of the region may bring another possibility of showers Sunday. Tuesday and Wednesday...Drier weather but still hot afternoon temperatures with highs in the 90s likely, especially away from the coast. Sea breezes are more likely Wednesday, with temperatures a bit cooler along the coasts that day. Otherwise, sunny skies and typical July weather. Thursday and Friday...This is the period of greatest uncertainty. Temperatures will cool a few degrees Thursday as clouds increase and a cold front starts to move through southern New England. The front moves the rest of the way through and offshore on Friday. This could result in temperatures down into the low to mid 80s Friday, quite a relief after the last week. Showers and thunderstorms will be possible with this frontal passage, particularly on Thursday when more instability is expected with both diurnal heating and partial sun. 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...High pressure will build in Saturday behind the front with mostly sunny skies and temperatures in the low to mid 80s once again. Sunday becomes a bit more uncertain with the possibility of a low pressure system developing or passing quite close to the RI/MA south coast. This could bring clouds, fog, and rain to the area, particularly near the south coast. Models disagree on how close to the coast this system gets, so quite a bit of uncertainty here. Still, confident enough to have chance pops in the forecast for Sunday. && .AVIATION /06Z 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 20Z and 02Z, 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. Timing of afternoon shra/TSRA may be off. KBDL TAF...Moderate confidence in TAF. Timing of afternoon shra/TSRA may be off. Outlook /Tuesday Night through Friday/... Tuesday and Wednesday...High confidence. VFR. Sea breezes likely to develop on both coasts Wednesday. Thursday...Low confidence. Mainly VFR. Periods of MVFR/IFR in SCT SHRA/TSRA Thursday afternoon and evening. Friday...Low confidence. Increasing clouds should lead to MVFR/IFR conditions in low clouds/fog and possibly additional SHRA. && .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. Light winds tonight, then pre-frontal southerly winds increasing to 10-20 kt Mon. Winds diminishing and becoming west later Mon night. Seas remaining below SCA. There is a risk for late day and evening thunderstorms Monday which will need to be watched. 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 from 11 AM this morning to 6 PM EDT this evening for CTZ002. MA...Heat Advisory from 11 AM this morning to 6 PM EDT this evening for MAZ010-011. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/RLG NEAR TERM...KJC/Doody SHORT TERM...KJC LONG TERM...RLG AVIATION...Doody/RLG MARINE...KJC/RLG CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.