Area Forecast Discussion
Issued by NWS Boston, MA

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101 FXUS61 KBOX 280734 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 332 AM EDT TUE JUN 28 2016 .SYNOPSIS...
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A slow moving cold front will bring scattered showers and a few thunderstorms into Wednesday, with the bulk of the activity occurring tonight. Dry and seasonable weather follows Thursday before the next front brings the risk for a few showers/thunderstorms late Friday and/or Saturday, but the majority of this time will be dry. Dry and pleasant weather with low humidity appears to be in the cards Sunday into Monday the 4th of July.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Scattered showers were on going early this morning. This hit and miss activity was the result of a shortwave and a burst of some marginal elevated instability, with the main focus for this activity to the northwest of Boston to Providence line. The bulk of these scattered showers should come to an end by mid to late morning, as shortwave departs. While warm advection will continue to result in the risk for a few spot showers, dry weather will dominate the rest of today with bulk of forcing/instability well to our northwest ahead of a cold front. Deep low level moisture will also result in considerable cloudiness at times, but still expect peeks of sunshine especially across southeast New England. High temps will mainly be in the upper 70s to lower 80s, but a few locales may reach into the middle 80s. It will also feel somewhat humid outside with dewpoints well into the 60s, something we have not seen much of so far this month.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
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***Scattered showers/thunderstorms with brief localized heavy rainfall possible between 9 pm tonight and 5 am Wednesday morning but severe weather threat is rather low*** Tonight... Showers and thunderstorms will be on going across Eastern NY early this evening. This activity will attempt to work into western MA/Northern CT by mid to late evening, but should weaken with diminishing instability/poor mid level lapse rates. Still may see some thunder and brief locally heavy rainfall in these locations. Greater threat for scattered showers/thunderstorms with brief locally heavy rainfall may set up across Eastern MA/Eastern CT and RI near or after midnight. This on the nose of a 30 to 40 knot southerly low level jet, MUcapes between 200 and 500 J/kg, and PWATS between 1.5 and 2 inches. Guidance not completely sold on where and if this sets up, but given the above parameters certainly a possibility. Severe weather threat looks rather low given limited instability/timing. Bulk of the activity should be offshore near daybreak. Low temps will mainly be in the 60s and may see some patchy fog develop. Wednesday... The actual surface cold front will sweep across the region on Wednesday. While the vast majority of the day will be dry, there is a low risk for a few strong thunderstorms developing Wed afternoon ahead of the front. Whether or not this activity develops hinges on if enough mid level moisture remains. While this is uncertain, the highest risk is across Eastern MA/RI where moisture will be a bit deeper. We should see 1000+ j/kg of Cape develop across Eastern New England ahead of the front along with 0 to 6 km shear values of 30 to 40 knots. Colder air moving in aloft will result in somewhat steeper mid level lapse rates, but nothing too extreme. The above parameters are supportive for the possibility of a few strong thunderstorms Wed afternoon. However, mid levels of the atmosphere will be drying out and may limit or prevent convection. So in a nutshell, there is a low risk for a few strong thunderstorms Wednesday afternoon with an isolated strong wind/hail threat if dry mid level air can be overcome. Highest risk across Eastern MA/RI between noon and 6 pm. High temps should generally reach into the lower to middle 80s away from the immediate coast. Still somewhat humid with dewpoints in the 60s.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Highlights... * Seasonable Thursday and Friday. * Another risk for showers and storms, late friday and the weekend. Overview and model preferences... PNA remains strongly positive through much of the long term with negative EPO. Therefore, the reflection across the CONUS remains nearly unchanged through the period. This is also partially thanks to a rex-type block with PACNW vortex leading to building ridge across the northern prairies, culminating in persistent longwave trof across the northeast. An initial shortwave will be exiting Wed along with an attendant cold front leading to a brief period of weak ridging until secondary shortwave from Hudson Bay reinforces the longwave trof by late in the week. This trof does take on a slight negative tilt suggesting a slightly stronger system, however the bulk of the jet forcing shifts into the Boreal forest regions of Canada. Therefore, the generally dry with only a risk for spot showers/storms are expected to continue through this long term cycle. Deterministic guidance is generally in good enough agreement that a blend should still work fine as a starting point. Details... Thu... Dry wx prevails under weak ridging with front settling offshore. H85 temps still near +12C, so another day with highs in the 80s and lows dropping back into the upper 50s and low 60s is expected. Fri into Sun... More significant differences here between available guidance, including the ensembles. Cold front will sweep through the region connected to low pres moving across ON/QC. Best forcing remains N, however decreased stability coincident with increase in PWATs back to nearly 1.5 inches suggest increasing risk for diurnally driven shra/tstorms. How quickly and ultimately how far the front moves offshore will define how long into Saturday this risk lasts. Secondary frontal wave development also possible, with the ECMWF leading the charge for Sun, suggesting some rain across the region from the S. Will maintain a low risk, but with settling trof, it may remain far enough offshore for little impact. Either case, a relatively unsettled period. Early next week... Another round of weak ridging within the longwave trof suggests a return to dry wx and seasonable temperatures.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/...
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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 Wednesday/... Today...Moderate confidence. MVFR conditions in low clouds to the northwest of a Boston to Providence line will probably improve to mainly VFR by afternoon. Bulk of scattered showers should also come to an end by mid to late morning. Otherwise, mainly VFR conditions expected the rest of the day. Tonight...Moderate confidence. Conditions lower to MVFR-IFR thresholds as boundary layer cools with an abundance of low level moisture. Scattered showers and thunderstorms also expected with main risk between 1z and 9z. Wednesday...Moderate to high confidence. MVFR-IFR conditions should improve to mainly VFR by afternoon as low clouds/fog patches dissipate. Low risk for a few strong thunderstorms Wed afternoon, mainly Eastern MA/RI. KBOS TAF...Moderate to high confidence in TAF. KBDL TAF...Moderate confidence in TAF. Outlook /Wednesday Night through Saturday/... Thursday-Saturday...Moderate confidence VFR. North winds become variable Thursday, then from the south Friday. Showers/tstms will develop over New York State, and may move into Southern New England Friday evening and night. These showers and storms would have areas of MVFR cigs/vsbys.
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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 Wednesday/...High confidence. Winds and seas will generally remain below small craft advisory thresholds through Wednesday afternoon. South to southwest wind gusts of 20 knots are expected at times with 2 to 4 foot seas across the open waters. Main concern is for areas of fog tonight into Wed am across the southern waters. May also see a few thunderstorms with brief heavy rain overnight. Outlook /Wednesday Night through Saturday/... Thursday-Saturday...Moderate confidence. High pressure builds over the waters Thursday and moves off to the east Friday. A cold front approaches from the west Friday night. Winds and seas should remain below Small Craft Advisory criteria. Scattered showers/thunderstorms possible Friday night as the cold front approaches.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...None.
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&& $$ SYNOPSIS...Frank NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Doody AVIATION...Frank/Doody MARINE...Frank/Doody

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