Area Forecast Discussion
Issued by NWS Boston, MA

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241 FXUS61 KBOX 251142 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 742 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 this afternoon and evening and again late next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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No major changes to the forecast this morning. Bought the forecast back in line with observed trends. Some showers around Long Island, but these appear that they will miss just about all of southern New England and the coastal waters. These showers are a sign of the increasing instability. Previous timing of convection in western MA still looked good. Previous discussion... ***Hot and humid, Late Day Severe Weather Possible*** Tricky balance to the forecast today regarding both the heat and convective potential for this afternoon and evening. Regarding the heat, have quite a bit of upstream convective cloud debris to contend to the SW combined with short-term guidance a bit cooler at H85, mainly between +18C and +20C, rather than the +20C previously progged. However, it will not take too much sun to allow mixing to reach H85 or higher, and with dwpts in sliding into the upper 60s to around 70, heat indices will approach 100. Currently, however, dwpts are starting lower than most guidance suggests, mainly in the 50s and low 60s. Therefore, given slight downslope flow, it still appears the lower CT valley has the best chance of reaching heat advisory criteria while others may fall just short, influenced by cloud cover and/or marine layer. Therefore, do not have the confidence to expand current heat advisories although several locations will see heat between 95F and 100F. Approaching shortwave is a bit faster than previously forecast. The impact here is that it`s too fast for upper lvl cold pool (and core of remnant EML) to lag the lift. Still, even with clouds, CAPE values between 1000-1500j/kg are likely. Shear values start mainly at or below 30 kt at both 0-3 and 0-6km, but do increase with the approaching shortwave toward the afternoon to around 35 kt. Although mid lvl lapse rates are not expected to be as robust given the lagging EML, this is still enough for typical diurnal convection to fire as the upper lvl shortwave approaches. The highest instability/shear overlap moreso across W MA/CT (after moving through NY), this correlates to current SPC SWODY1 Marginal Risk, down from a Slight Risk. This suggests SPC shares concern for the mitigating factors. Expect convection to begin firing mainly around 2PM or after across NY. The primary issue will be strong-damaging winds, as inverted-V profiles and high D-CAPE values support this once again. Hail a risk as well thanks to about 300j/kg CAPE between -10C and -30C, but WBZ heights are rather high. High PWATs near 2.0 inches by late afternoon and low magnitude Corfidi vectors all support a heavy rain with localized urban flooding threat. The shear values and high LCLs typically do not support much of a tornado risk, but given stronger stability or a localized boundary, will still need to monitor. Stay tuned to later updates through the day as timing and any warnings ultimately are issued.
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&& .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 /11Z MONDAY THROUGH FRIDAY/...
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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 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. Light seabreze has already developed. Wind direction may vary through 15Z, after which stronger seabreeze should be in place with a more steady direction. KBDL TAF...Moderate confidence in TAF. Timing of afternoon shra/TSRA may be off. 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.
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&& .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 late day and evening thunderstorms today 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...Belk/Doody NEAR TERM...Belk/Doody SHORT TERM...Doody LONG TERM...Belk AVIATION...Belk/Doody MARINE...Belk/Doody CLIMATE...staff is the U.S. government's official web portal to all federal, state and local government web resources and services.