Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 010220 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1020 PM EDT WED AUG 31 2016 .SYNOPSIS...
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A cold front over the Great Lakes sweeps across Southern New England Thursday. This will bring scattered showers and a few thunderstorms through that time. High pressure will bring dry and seasonable weather Friday and Saturday, then we will have to closely monitor the track and intensity of Tropical Storm Hermine as it lifts north along the eastern seaboard. Some rain and wind is possible Sunday into Monday but there is still a lot of uncertainty. The actual track and intensity of Hermine will determine the magnitude and extent of impacts for southern New England.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Radar showing light echoes moving through CT/RI and SE MA. But surface obs show these showers falling from 10-12 thousand foot cloud bases and little change in the clouds for the next few hours. Upper jet of 90-100 kt moves over New England toward morning and may provide better dynamic support for showers. Precipitable water values approach 2 inches so a few locally heavy downpours possible. Forecast temps at 10 pm needed to bumped higher by a couple of degrees. Because of this we bumped min temps up 1-2 degrees as well.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
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Thursday... Frontal boundary looks to stall and begin a slow- washout process across E MA/RI during the afternoon. The risk for shra/tstms continue with SB CAPES still mainly near or above 500j/kg. Front will provide a focus for sfc convergence, which models seem to indicate well. So after a brief lull from the first LLJ during the AM hours, a lull should allow for a reloading of the sounding for the afternoon. Therefore, feature a secondary risk for afternoon showers and storms mainly across E MA and RI. Once again the highest risk is for brief heavy rainfall thanks to the maintenance of high PWATs, with only a modest risk for any SVR as shear/instability profiles remain modest themselves. Temps remain near normal thanks to cloud cover lingering across the region through much of the day. Expect only mid-upper 70s for highs. Thursday night... Modest ridge building as the upper lvl trof continues to shift. E. This should lead to enough drying for an end to precip risk across the region as well as some clearing. The combination of lowering dwpts and clearing skies may allow min temps to drop back into the 50s and low 60s once again, not as humid as previous nights.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... HIGHLIGHTS... * Mainly dry and seasonable Fri/Sat but a few showers possible Fri * Potential impacts from Hermine may be felt Sun/Mon but will depend on track/intensity * Rough surf and rip currents this weekend into early next week * Increasing heat and humidity toward middle of next week Overview... Model guidance is in decent agreement on the overall large scale pattern leading into next week but obviously there are significant differences in the details regarding the track/intensity of Tropical Storm Hermine. 12z guidance suite has trended further west as it attempts to phase shortwave energy dropping south from the Gt Lakes with Hermine eventually transitioning to a well developed baroclinic wave as it lifts north over the Mid Atlc region this weekend. GFS and CMC global are on the western edge of the guidance envelope while UKMET is furthest east with ECMWF in between. There is some clustering of the GEFS members along the coast but also variability. A wildcard with this storm is strong blocking ridge developing to the north which will slow and eventually halt its northward movement with this system possibly remaining south of New England before it weakens and lifts out around Tue and this could keep the most significant rain/wind impact to the south. However, this is still a day 4/5 event and there are many variables in play, especially the extent of interaction of Hermine with shortwave energy dropping down from the north and how the blocking ridge comes into play which will affect the track and intensity of Hermine. We`ve seen significant model fluctuations within 48 hours of winter storm events and it is almost certain there will be more variations in model solutions to come due to the complexity of the situation. The main impact will likely occur Sun into Mon but the magnitude and extent is uncertain. Friday... Cold front is offshore but models show mid level trof passage and assocd cold pool with 500 mb temps of -14 to -15C moving across the region. Models are not generating any instability as dewpoints are low but can`t rule out an isold shower or 2. Seasonable temps in the 70s. Saturday... High pressure should remain in control bringing a continuation of dry and seasonable conditions. Sunday through Monday... This should be the timeframe of main impact from Hermine, with best chance of rain and wind risk during this period, especially Sunday. The track and intensity will determine the extent and magnitude of rain/wind with potential impacts ranging from just light rainfall and minimal wind threat to a worst case scenario of 2 to 4 inches of rain and moderate wind threat with gusts to 40+ mph. Astro tides are very low and coastal flooding threat is low although some coastal erosion is possible if a stronger solution verifies. Bottom line, continue to monitor the latest NWS and NHC forecasts to be prepared. But, nothing is set in stone at this point and forecasts will likely change between now and the weekend. Tuesday and Wednesday... What is left of Hermine will be lifting out with strong mid level ridge building into the region. This will result in increasing heat and humidity through the middle and end of next week but timing will depend on how quickly Hermine exits. Potential for 90+ degree heat by next Wednesday. && .AVIATION /02Z THURSDAY THROUGH MONDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Overnight and early AM...moderate confidence. Increased risk for shra, some of which may be heavy at times. Low risk for isolated TS. VFR likely dominates central/E MA and RI, with a risk for some MVFR/IFR cigs and vsbys late across W MA and CT. Thursday...high confidence. A return to mainly VFR all terminals. Although a risk for shra/tstms continue especially E of a line from NYC-IJD-MHT. These may include some MVFR/IFR conditions. Sea breezes possible. Thursday night...high confidence. Risk for shra ends NW to SE through the night with gradual clearing. VFR dominates. KBOS Terminal...High confidence in mainly VFR through the period. Lower confidence in shower timing or sea breeze development tomorrow. KBDL Terminal...Moderate confidence, mainly due to uncertainty in MVFR risk overnight. Outlook /Friday through Monday/... Friday and Saturday...High confidence. VFR. Low risk of a few showers Fri. Sunday and Monday...Low confidence. Conditions will depend on track/intensity of Hermine. Potential for IFR with rain and gusty winds.
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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. Lingering swell will gradually dissipate tonight as Tropical Depression 8 and and Gaston continue to move away from S New England. Small craft advisories should be able to be dropped. Otherwise, low risk for some shra and T-storms into tomorrow evening with localized rougher seas, but once the small crafts drop tonight, it should remain below small craft thresholds through the remainder of the period. Outlook /Friday through Monday/... Friday through Saturday...High confidence. Expect winds below SCA with north gusts to 20 kt Fri and NE gusts to 20 kt over southern waters Sat. Swell may approach 5 ft over outer waters. Sunday and Monday...Low confidence. Lots of uncertainty for this time period as forecast will depend largely on track/intensity of Hermine. Potential for tropical storm force wind gusts and building seas. Mariners should closely monitor the latest forecasts.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 5 AM EDT Thursday for ANZ250-254. && $$ SYNOPSIS...KJC/Doody NEAR TERM...WTB SHORT TERM...Doody LONG TERM...KJC AVIATION...WTB/KJC/Doody MARINE...WTB/KJC/Doody

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