Area Forecast Discussion
Issued by NWS Boston, MA

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789 FXUS61 KBOX 201911 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 311 PM EDT WED JUL 20 2016 .SYNOPSIS...
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Dry yet warm conditions are expected for Thursday. Heat and humidity return Friday along with the risk for scattered showers and thunderstorms during the afternoon and evening, some of which may be severe. Hot weather is expected to continue this weekend. An approaching cold front may bring us some relief from the heat and another round of scattered showers and thunderstorms sometime Monday and/or Tuesday.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Tonight... Perhaps some scattered mid to high level clouds sweeping across the NE CONUS within the NW cyclonic flow, otherwise dry, cool, and comfortable. Another fantastic night! High pressure in control as the ridge builds in from the W and surface high pressure shifts S/E. Will see return W/SW flow emerge during the overnight period but overall light. Considering this and mostly clear conditions, anticipate another evening of radiational cooling. Lows around the mid to upper 50s, warmer along the coastlines and within the urban centers. Slightly warmer than the previous night, but subsequent of the return S flow and moderation in airmass with rising dewpoints.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
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Thursday... Mid to upper level ridging building across the NE CONUS as high pressure is situated offshore. Light W/SW winds at the surface with sea-breezes along the immediate shores. Low to mid level flow turning W ushers in a +14-16C H85 airmass aloft. Deep boundary layer mixing, anticipating another round of dry conditions at the surface with highs getting into the mid to upper 80s, a few locales likely coming in at or above 90 (namely the lower CT and Merrimack River Valley). Mostly clear conditions, perhaps some scattered diurnal cumulus and/or mid to high level clouds from the N/W. Thursday night... Drier air lingers parent with the mid-upper level ridge shifting S/E offshore. Synoptically, anticyclonic flow persisting through which lead mid level vortex energy is diving S/E into S New England by Friday morning. Anticipate increasing clouds out of the N/W with model sounding indications of top-down moistening. But still a lot of dry air to contend with so expect most of the region should remain dry overnight. Perhaps a slight chance of showers over NW MA given indications of better moisture availability and mid to upper level forcing. Surface winds turning more southerly and increasing with the potential for 15 to 20 mph gusts along the S-shore, will see an increase in dewpoints at the surface back into the 60s. Similar lows, could see some patchy fog develop.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Highlights.. * Heat and humidity return Friday through the weekend * Risk of showers/thunderstorms, some severe possible Friday * Another cold front may bring showers and storms again Monday Overview...The focus of the long term forecast will be on the thunderstorm potential for Friday, therefore, won`t go into that much here. Aside from that, hot and humid weather continues into early next week. A cold front late Monday into Tuesday will likely bring a little relief from the heat as well as another chance of showers and thunderstorms Monday afternoon and night. High pressure then builds over southern New England Tuesday and Wednesday. Overall, the models are in fairly good agreement on the synoptic pattern for this period. As always, there are slight timing differences and certainly mesoscale patterns that have yet to be resolved, however, for the bulk of the long term, see no problem using a blend of the models. For temperatures, Friday into the weekend, will likely raise the blend by a few degrees to retain the heat a bit better than the blend. Friday...Main concern for the long term is the thunderstorm potential. There are many things that are seemingly coming together for thunderstorms and even a few severe thunderstorms to be possible. However, there are still some potential kinks in the system that could limit the instability, etc. Other than the potential for storms during the afternoon and evening, much of the day will be dry but hot and humid with temperatures climbing into the low to mid 90s for much of the region. Positives for thunderstorm development and severe potential: - a shortwave moving across northern New England - low pressure in Quebec pulling first a pre-frontal trough and then a cold front through southern New England - decent shear (about 30 kts from 0-6km) - increasing dewpoints - strong low level jet (35-45 kts at 925mb) Negatives or questionable elements: - surface CAPE increasing to over 1000 J/kg during the afternoon (This will be dependent on sunny skies during the morning and early afternoon, which is of question. There is potential for lingering overnight convection over the Great Lakes to move over southern New England during the morning hours, with cloud debris limiting the instability potential.) - remnant EML moving over southern New England (The GFS specifically shows this better than either the NAM or ECMWF. While there is some evidence of a mixed layer on the NAM and ECMWF, it`s not as defined or strong as it is on the GFS, and is focused more across northern New England than southern New England.) All that to say, there is certainly potential for severe thunder- storms Friday afternoon and evening, as indicated in the Day 3 SPC outlook. However, as indicated yesterday in this discussion, so much of severe weather comes down to the mesoscale which is rarely clear this far out. Timing of all these features and the development of the instability during the day Friday will all be factors in determining how widespread any severe weather is, should it develop. Those with outdoor plans on Friday should keep a close eye on the weather over the next day or so. Saturday and Sunday...Could see some showers lingering into Saturday if the cold frontal passage is a bit slower than currently forecast. Otherwise, much of the weekend should be dry, though hot and humid. Temperatures will soar well into the 90s for much of the area with dewpoints in the mid 60s under mostly sunny to sunny skies. Monday...Low pressure moves through Quebec bringing another cold front through southern New England late Monday into early Tuesday. This will likely bring a bit of relief from the heat and humidity of the weekend. In addition, another round of showers and thunderstorms is possible. At this point, this looks like your garden variety diurnal showers and thunderstorms, but will need to keep an eye on it through the weekend. Tuesday and Wednesday...Behind the cold front, high pressure builds into southern New England. This will result in quiet, dry weather. Temperatures/dewpoints will be a bit cooler than the weekend but will remain in the normal range for late July.
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&& .AVIATION /19Z WEDNESDAY 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 Thursday Night/...High Confidence. 18z update... Rest of today... VFR. Will remove the mention of sea-breezes. Light NW flow dominant. Tonight into Thursday Night... VFR with winds turning W/SW. Could see gusts up around 15 kts along S-coast terminals late Thursday, perhaps as high as 20 kts into Thursday night. Increasing mid to high level cigs from the N/W late in the period with a chance of SHRA for NW MA. KBOS TAF...VFR. KBDL TAF...VFR. Outlook /Friday through Monday/... Friday...Moderate confidence. Mainly VFR conditions expected. Brief periods of MVFR/IFR conditions possible in SCT SHRA/TSRA. A few of these storms may become severe, producing strong, gusty winds and large hail. Saturday...Moderate confidence. Mainly VFR. Could see some lingering MVFR conditions in lingering -SHRA or areas of fog in the morning hours. Sunday...High confidence. VFR. Monday...Moderate confidence. Mainly VFR conditions expected. Brief periods of MVFR conditions in SCT SHRA/TSRA possible.
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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 Thursday Night/...High confidence. Increasing S winds late Thursday into Thursday night as high pressure persists mainly S/E of the waters ahead of an approaching cold front for Friday night into early Saturday. Gusts up to 20 kts possible for the S/SE waters allowing waves to build close to 5 feet. Will hold off on small craft advisories conceding that stronger gusts at or in excess of 25 kts will occur beginning Friday morning. Outlook /Friday through Monday/... Seas increase Friday and Friday night as a cold front approaches and then moves over the coastal waters Friday night into Saturday morning. Seas could reach 5 to 7 feet on the outer waters during this time. They then gradually subside through the weekend before increasing again slightly in response to another approaching front late Monday night. Small craft advisory conditions are expected Friday and Friday night with southwesterly winds increasing to 15 to 20 kts with gusts in the 25 to 30 kt range. Otherwise, winds will remain below 25 kts through the weekend and into Monday. Showers and thunderstorms are likely possible over the waters Friday evening and night and again on Monday afternoon. Storms Friday may become strong, producing dangerous boating conditions at times. In addition, areas of fog may develop on Friday night, limiting visibilities.
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&& .FIRE WEATHER...
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While winds are forecast to be light on Thursday, dry conditions continue. Massachusetts State Fire Weather Officials have advised given the forecast warm temperatures into the upper 80s to low 90s, low humidity values, and lack of rainfall as of late that there is a heightened fire danger. Such conditions though do exist for other parts of S New England, that being in CT and RI.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...RLG/Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...RLG AVIATION...RLG/Sipprell MARINE...RLG/Sipprell FIRE WEATHER...Sipprell

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