Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 280734 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 334 AM EDT THU JUL 28 2016 .SYNOPSIS... Offshore high pressure will bring warmth and humidity to Southern New England today. A cold front over Northern New England drops through our area late in the day and may bring scattered showers and thunderstorms. Low pressure then moves up the front Friday and brings more widespread rain and scattered thunder. Seasonable and dry weather for Saturday. Shower chances return for Sunday into Monday. Looking dry with a moderating warming, muggy trend through the remainder of the week. && .NEAR TERM /THROUGH TODAY/... Closed low over Northern Quebec and a broad subtropical high across the Southern USA continue to channel jet flow across the northern tier of the USA. One shortwave and associated 95 knot jet will move across Upstate NY and Northern New England today. All models show stability parameters focussed on Northern NY and VT/NH...Totals in the upper 40s, mid level lapse rates 6.2-6.5 c/Km. Both the ECMWF and GFS show best upper venting over Srn VT and Srn NH. But both the dynamics and instability are close enough for Northern MA to be affected. We will continue to feature chance pops for showers/tstms in this area during the afternoon. Plenty of sun during the morning and early afternoon to allow deep mixing, reaching to 800 mb and tapping 13-14C air. This would support max surface temps in the low to mid 90s. Southwest flow should minimize the extent of any sea breezes. It should also draw higher dew points north into our area this afternoon. && .SHORT TERM /TONIGHT THROUGH 6 PM FRIDAY/... Some leftover convection possible this evening/early night in Northern/Western MA as the cold front settles through our area. This should diminish with the setting sun and as a weak shortwave ridge races overhead early at night. Attention then turns to another shortwave, this one coming through the Ohio Valley later tonight and across the Northeast on Friday. The previous model suite gravited to two scenarios. One scenario showed the associated surface low passing close to New England and bringing us a soaking rain, while the second scenario kept the surface low and most of its rain offshore. The overnight suite has converged on the first scenario, which we will follow with this forecast. Low level jet feeds high moisture content air starting around 12Z Friday. This suggests timing the rain for late tonight through Friday afternoon. Precipitable water values are forecast between 2 and 2.5 inches...very juicy air...so the potential will exist for locally heavy downpours embedded in the rain area. Aside from run-to-run consistency, the question remains as to where the axis of heavy rain will set up. The stalled cold front is the most likely feature to focus low level lift. This would be somewhere near the South Coast. The projected tracks of the surface low also favor the South Coast area with heaviest rain along and just north of the low. We used a blend of RFC and WPC rain data for our own forecast. Broad area averages will be an inch to 1.25 inches. Within this, locally heavier amounts up to 2.5 inches is possible. We have considered the possibility of issuing a flood watch but will hold off until the day shift to see if the next model suite remains consistent with the overnight. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... */ HIGHLIGHTS... - Seasonable and dry for Saturday - Chance of wet weather for Sunday into Monday - Warming and becoming more muggy through the remainder of next week */ DISCUSSION... Saturday... High pressure in control with a slightly cooler airmass aloft with H85 temperatures around +12-14C. Looking at seasonable temperatures with light and variable winds likely yielding sea-breezes along the shores. Thinking just some scattered mid to upper level cloud decks from upstream convection and troughing over the Ohio River Valley, otherwise quiet weather. Sunday... Not ready to call it completely dry. While high pressure exiting to the E with a measure of dry and air low to mid level anticyclonic flow lingering, there is a fairly potent mid-level H5 trough axis and attendant vortex energy sweeping the NE CONUS. Tapping into S moisture and likely more favorable destabilization S/W of our region feel some rainfall is possible for S New England late into the overnight period. Monday... Timing of the mid-level H5 trough critical. There may be a window of opportunity in where the e-half of New England destabilizes ahead of synoptics. Thus PoP chances continue but low confidence as forecast solutions differ on outcomes and timing. Some measure of rainfall does seem possible so long as we can tap into S moisture rather than being robbed by a possible emerging Mid-Atlantic low. Rest of the week... Keep it dry though diurnally forced convection is not out of the question. Greater confidence to the N/W as NW flow aloft persists pushing cooler temperatures aloft across the region. Looking at a period of warming temperatures with a return of muggier conditions. Next system worth of note may not be till Thursday. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Today... VFR with a developing South-Southwest flow. Scattered showers/t-storms possible north of the MA turnpike during the afternoon/evening with brief MVFR/IFR in any storms. Tonight and Friday... VFR before midnight. Rain and scattered thunderstorms developing after midnight. Ceilings/vsbys will lower to MVFR/IFR late at night and Friday in this precipitation. Conditions may start improving from west to east Friday evening. KBOS TAF...High confidence through midnight. Low-moderate confidence after midnight. KBDL TAF...High confidence through midnight. Low-moderate confidence after midnight. Outlook /Friday Night through Monday/... Saturday...Moderate confidence. VFR. Light W/NW winds with sea-breezes developing along the shores. Sunday into Monday...Low confidence. Chance SHRA with S winds. Will hold VFR. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Winds remain below 25 knots and seas below 5 feet through the period. There is a low confidence potential for 25 knot winds on the southern outer waters Friday afternoon. Rain, heavy at times, with possible thunderstorms. This will bring periods of poor visibility. Outlook /Friday Night through Monday/... Saturday...Moderate confidence. Light W/NW winds with sea-breezes developing along the shores. Waves below 5 feet. Good boating weather. Perhaps some showery weather lingering over the SE waters during the morning. Sunday into Monday...Low confidence. Chance showers with winds out of the S. Possible thunderstorms. Will hold waves below 5 feet. && .FIRE WEATHER... Dry conditions will persist today, except possibly in western and north central MA where scattered showers/storms may bring localized rainfall Thu afternoon. Minimum RH values of 30 to 40 percent are expected across much of southern New England, except 40 to 60 percent on the South Coast, Cape Cod, and the Islands. South to southwest winds will stay under 20 mph. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for CTZ002. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/Sipprell NEAR TERM...WTB/Sipprell SHORT TERM...WTB LONG TERM...Sipprell AVIATION...WTB/Sipprell MARINE...WTB/Sipprell FIRE WEATHER...

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