Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191956 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 356 PM EDT Fri May 19 2017 .SYNOPSIS... A cold front moving over Southern New England will move offshore this evening. High pressure from Canada will build south over our region tonight and remain in place for much of the weekend. More seasonable weather is expected for the weekend into early next week. Dry initially then turning wet Monday ahead of a sweeping cold front. A brief reprieve Tuesday prior to more rain expected mid to late week along with continued near-seasonable conditions. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... This evening... Still watching convective potential for the late afternoon and evening hours. Drier air has moved into areas north of the Mass Pike with dew points in the 50s. Higher values remain to the south. One shower fired near White Plains NY early afternoon. The HRRR forecasts scattered convection to fire over parts of CT- RI and SE Mass until 00Z. The instability is in place with CAPE forecast near 1500 J/Kg over those areas. Certainly warm enough with sfc temps reaching 88-91. Moisture remains limited, but could be just enough for widely scattered showers/t-storms to form. We will continue our POPs from the earlier forecast, generally slight chance or low-end chance over RI and SE Mass. Tonight... High pressure builds south from Canada tonight. clearing skies and drier air will overspread all of Southern New England. Dew points will fall back into the 40s and eventually the 30s. This will make room for temperatures to fall back into the 40s inland and low 50s near the shore. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... Fair weather day with high pressure build in. Some high clouds may linger to the south and southwest, but otherwise a sunny day. Mixing should again reach at least 850 mb, where temperatures will be 4-6C. That would support max temps in the mid and upper 60s. If we mix higher, which is very possible in the interior, temps would reach the lower 70s. Winds will turn northeast in eastern Mass and RI in response to the position of the high center. There could also be a sea breeze component along the immediate coast. Either way, temps in eastern Mass should be cooler than farther west. We will go with a range of 60s east to lower 70s west. Saturday night... Fair skies and light wind. Dew points in the mid 30s to low 40s. Expect min temps in the upper 30s to mid 40s. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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*/ Highlights... - Seasonable and dry for Sunday - Rain with embedded heavier showers for Monday - Dry on Tuesday - Wet for the mid to late week period, remaining near-seasonable Overview and model preferences... The ridging Rex-like block allowing for the nice weekend will be shifting to the E by Mon as the upstream cutoff moving out of the Plains to the Great Lakes interacts with deep trof near Hudson Bay. This forces the cutoff further E and digs/deepens it toward the SE through the end of the week. This provides a conduit for several shortwaves within the cyclonic flow on the E side of the cutoff. Therefore, as previous forecaster noted, an active pattern sets up with periods of showers/storms possible, but not a washout as each individual wave will be followed by weak ridging yielding breaks. Noting fair agreement here between models such that a blend of guidance can be used as a baseline for this long-term forecast update. Details... Sun... The pleasant weekend continues. Plenty of sunshine under high pres which remains in control. May be a few late day clouds building over from the W, but this should not limit the pleasant conditions. H85 temps warm through the period starting around +4C at 12Z but reaching +8C by late afternoon. This should allow temps to inch back into the low-mid 70s away from coastal areas which will be cooled by sea breezes. Sun night into Mon night... Occluding low pres sliding into Ontario and Quebec will be pushing its occluding fronts through the region by daytime Mon. In fact, noting the possibility of triple point low pres formation, slowing the system down by Mon evening. This should be enough lift to interact with modest moisture (PWATs reach about 1.5-1.8 inches) and allow for a period of wet wx with embedded heavier downpours through the period, starting from W-E Mon morning. The risk for downpours amplifies by the potential triple point low. Modest convective risk also adds to the risk for heavier downpours as SLIs are noted to dip to near 0 with some conditionally unstable lapse rates. Therefore, could see widespread rainfall totals of 1.00-1.50 inches with the possibility of a few higher amounts where heavier rains are observed. Flooding risk is very low given the progressive nature leading up to the triple point development. Typical nuisance and poor drainage flooding are the potential impacts here. Did undercut guidance somewhat for highs especially Mon, with the warm front likely never making it through New England (especially given the triple point risk) leaned more heavily on raw model 2m temps which were much cooler. Tue into Wed... Modest ridging is noted in the mass fields this period as the upstream cutoff continues to slowly dig/deepen across the lower Great Lakes. This should allow for a reprieve from precipitation for the most part across the region as the amplifying pattern will slow shortwave progression. Will generally highlight another two day stretch of generally nil POPs given this ridging and associated high pres. H85 temps remain near +10C through the period suggesting highs in the low 70s for the most part while lows (assuming enough clearing could dip in the upper 40s and low 50s). In essence, near seasonal normals. Thu into Fri... Strong shortwave looks to rotate through the longwave trof/cutoff forcing the whole pattern to shift E. Tapping into Gulf of Mexico moisture and yielding good lift, we are looking at low pres development E of the Appalachians then sliding NNE to once again yield a prolonged period of wet wx with pockets of embedded heavier rain. Timing somewhat uncertain given the pattern, in fact at this point, its likely too fast pushing most of the rain through on Thu. This is a typical long-range bias with highly amplified flow.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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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 Saturday Night/... This evening... Moderate confidence. VFR. Widely scattered showers/t-storms over RI and SE Mass, especially along the south coast. This activity diminishes by 8 pm. Tonight...High Confidence. VFR. Mostly clear. Northwest winds turning from the north. Saturday...High confidence. VFR. Onshore wind expected along east coastal MA. North winds continue in the interior. Saturday night...High confidence. VFR. Mostly clear skies, light wind. KBOS TAF...High confidence. VFR expected through the period. Note wind shifts to be from the east on Saturday afternoon. KBDL TAF...High confidence. VFR expected through the period. Outlook /Sunday through Wednesday/... Sunday...High confidence. VFR. S winds at or below 10 kt most of the day. Sea breezes expected all coastlines. Sun night into Mon night...Moderate confidence. MVFR-LIFR. Lowest conditions likely for the S-coast with potential fog/rain impacts. Increasing S winds with gusts up to 25 kts. RA/+RA at times. Low risk TSRA. Possible LLWS impacts with S/SW winds 2 kft AGL 40-50 kts. Tuesday into Wednesday...Moderate confidence. Improvement expected Tuesday with mainly VFR conditions W winds shift to S-SW. Wednesday uncertain, but mix of VFR is possible although if rain occurs, predominant MVFR/IFR expected.
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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 Saturday Night/...High confidence. Lingering 5 foot seas on the southern and southeast outer waters this evening, but this should diminish this evening. A cold front moves across the waters early tonight. Winds then turn from the northwest and eventually from the north. Winds will be less than 25 knots and seas less than 5 feet through the night. High pressure builds over the waters Saturday and Saturday night. Winds turn from the northeast Saturday and then become light variable Saturday night. Seas will remain less than 5 feet. Outlook /Sunday through Wednesday/... Sun and Sun night...High confidence. Quiet boating weather expected winds will shift to the S on Sun. Mon into Mon night...High confidence. Period of Small Craft Advisory conditions as low pres passes along the S waters. Winds will shift out of the S to the SE late Mon, then to the W-NW Mon night. Wind gusts 25-35 kt expected, with a risk for low end Gales. Seas will build to 5-7 ft on the ocean waters. Tue and Wed...Moderate confidence. W winds shift to the E on Wed. At this time, it appears winds/seas should remain below Small Craft Thresholds, however there is some uncertainty in the pattern by mid week that may change this thinking.
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&& .CLIMATE...
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High temperatures through 4 pm... BOS 90 90 (1986) PVD 91 New record, old record 89 (1906) BDL 92 94 (1962) ORH 84 92 (1962) Lost in the talk of high temperatures... all four climate sites broke their high minimum temperatures on Thursday. BOS 71 Old record 63 (1896) PVD 70 Old record 62 (1943) BDL 67 Old record 64 (1906) ORH 69 Old record 63 (1943)
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ254>256.
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&& $$ SYNOPSIS...WTB/Doody NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Doody AVIATION...WTB/Doody MARINE...WTB/Doody CLIMATE...

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