Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 230757 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 357 AM EDT SAT JUL 23 2016 .SYNOPSIS... Hot conditions continue today, along with another risk for thunderstorms this afternoon, some of which may become severe. An approaching cold front will bring another round of scattered showers and thunderstorms Monday night and Tuesday. More warm weather follows midweek. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Pre-frontal trof is currently shifting through central S New England as initial upper lvl shortwave/associated cold pool are moving offshore. While some moderate convection continues in advance, the bulk of this should remain offshore for the rest of the morning hours. Very weak post convective ridging is clearing things out to the NW. This clearing will allow for atmospheric reloading so-to-speak through the morning. In fact, guidance is likely underdoing today`s diurnal destabilization as progged dwpts/temps are initializing lower than current obs suggest. H85 temps only drop to about +18C, so another day (given plenty of sunshine to start) with temps in the upper 80s to low-mid 90s is likely. Dwpts only drop into the upper 50s to mid 60s behind the stalling boundary. Other than heat, will need to monitor for another round of potential severe wx today thanks to another round of instability with ML CAPE values near 1200j/kg. Very acute shortwave combined with H5 temps dropping to near -13C suggest one last taste of the remnant EML which helped convection overnight. Noting mid lvl lapse rates will approach 7.0C/km with this upper lvl cold pool. Therefore primed for another round of TS today, peak timing of the shortwave suggests a slightly earlier start/end, mainly 18Z (2PM) to 01Z (9PM). Primary issue will once again be wind, as mean shear exceed 40 kt with H92 winds nearly 40 kt, and high D-CAPE values thanks to a well mixed BL. Would not be surprised to see localized downburst and straightline wind damage similar to Saturday evening. Although this shear could allow for storm organization, tornado risk should once again be low thanks to very LCLs and a well mixed BL. Hail also a risk, as high lapse rates once again support hail CAPE values mainly +300j/kg. Therefore, stay tuned to forecast updates through the morning as this thinking correlates to latest SPC SWODY1 Marginal Risk. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Thunderstorms/showers should end earlier than Saturday night thanks to faster movement of the forcing shortwave. Drier air will lead to some drying during the overnight but leftover convective debris cloudiness will likely keep temps from dropping too far. Expect mins mainly in the 60s. A few spots of fog possible, especially where late day rainfall is observed. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Big Picture... High pressure covers the Southern and Central USA much of the week. A zonal flow extends across Canada and the USA Northern Tier. Shortwaves in that zonal flow will move through New England Monday night and again on Friday. In between, parts of the large high will push up over our area. Forecast contour height fields remain higher/warmer than normal levels through the period, so expect temperatures to run warmer than normal most of the time. Details... Sunday... High pressure in place through the day. Some signs on the GFS and ECMWF that a twist may develop in the flow in Eastern MA that could generate an eastern coast sea breeze during the afternoon, but low confidence at this time. Solar mixing to near 850 mb with temps at 850 mb forecast at 16-17C. This would support max sfc temps inland at 87-91F, with ocean buffering keeping levels near 80 Cape and Islands. Northwest flow will bring lower/drier dew points of 55 to 60 inland and lower 60s along the South Coast. Light wind Sunday night. Some increase in high clouds and slowly increasing dew points should keep min sfc temps in the 60s, although upper 50s not out of the question in some normal cool spots. Monday... Shortwave drives low pressure across Eastern Canada with a cold front sweeping across NY during the day and New England Monday night. Most of the day should be rain-free. Some signs of marginal instability crossing during the morning which may be a warm front with a couple of light showers. Better instability moves in from the west during the afternoon and evening. Totals forecast in the upper 40s and mid-level lapse rates 6.2 to 6.5 C/Km. Precip Water values climb to near 2 inches. This would support thunderstorms, some with heavy downpours. Winds of 20-25 kt at 850 mb and 35 kt at 500 mb suggest potential for strong gusts in convection. Expect scattered afternoon/early night convection with local downpours. Temps of 18C at 850 mb supports another day of max temps in the low 90s. Tuesday-Wednesday... High pressure takes control and brings fair weather. Temps aloft will again be 16-18C which will support upper 80s and lower 90s. Thursday-Friday... Next upper shortwave moves through during this time. Both GFS and ECMWF seem inconsistent with their surface features but indicate at least one cold front moving through during this time. We will show chance pops in western sections Thursday afternoon and all areas Friday. Low confidence in details at this time. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/... Through 12Z...moderate confidence. Mainly VFR except localized ground fog. Areas of TSRA will dissipate across SE MA through 08Z, giving way to clearing there as well. Winds mainly 10-20 kt outside of TSRA where gusts to 40 kt are possible. Today...moderate confidence. VFR through at least 18Z. Then another risk for sct TSRA possible mainly E of a line from EEN-ORH-WST. Some strong winds possible once again in some of these storms. Otherwise, winds mainly W-SW 10-15 kt. Tonight...High confidence. Mainly VFR after any storms/showers end through the overnight hours. KBOS TAF...Moderate confidence. Another round of thunderstorms is likely this afternoon to early evening. Some of those storm could produce strong wind gusts. KBDL TAF...High confidence of VFR prevailing. There could be some patchy fog with MVFR visibility through 12Z. Outlook /Sunday Night through Wednesday/... Moderate-high confidence. Sunday...VFR. Possible areas of IFR in early morning fog. Monday... VFR. Possible IFR in early morning fog. Brief MVFR/IFR cigs/vsbys in afternoon and early night showers/tstms. Tuesday-Wednesday... VFR. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through tonight/...High confidence. Seas will continue to dissipate through the morning as winds outside of thunderstorms have already dropped to or below 20 kt. Seas will also gradually dissipate this morning allowing the remaining small craft advisories to be dropped. Otherwise, another round of showers and thunderstorms are possible over the waters this afternoon and evening which could contain localized strong wind gusts. Outlook /Sunday Night through Wednesday/... Moderate confidence. Winds less than 20 knots and seas less than 5 feet through the period. A cold front will bring scattered showers/thunderstorms Monday afternoon and night, with potential for strong wind gusts and brief poor vsbys in heavy downpours. && .EQUIPMENT... The KBOX radar continues experience calibration issues causing reflectivity values to over-estimate. Technicians are expected to work on the radar this morning, which will also lead to a period of downtime through the morning hours especially. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ235- 237-255-256. && $$ SYNOPSIS...Belk/Doody NEAR TERM...Doody SHORT TERM...Doody LONG TERM...Belk AVIATION...Belk/Doody MARINE...Belk/Doody EQUIPMENT...staff

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