Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251932 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 332 PM EDT Sun Sep 25 2016 .SYNOPSIS... High pressure will center over New England tonight and allow for efficient radiational cooling. A low pressure area and associated front will bring showers to the area late Monday night into Tuesday morning. Considerable forecast uncertainty exists for the rest of the week. An easterly flow may persist for the rest of the week with a chance of showers or areas of drizzle from time to time, especially near the south coast. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Surface high pressure crests over the area tonight and sets the stage for efficient radiational cooling under clear skies and with light winds. using minimum temperatures of 35F or lower as a guide, have expanded the Frost Advisory some from the initial issuance this morning to include far NW Middlesex County, Norfolk County, eastern Hampden and southern Worcester Counties. Feel reasonably confident about Norfolk County. Some of the other areas unlikely to be validated with ASOS data but think rural areas of eastern Hampden and southern Worcester County have a fairly good chance at temperatures near or a little below 35F for a few hours with virtually no mixing. Anticipate that we may experience patchy frost across other portions of more rural Middlesex County and our northern CT zones but probably not extensive enough to warrant an advisory. That can be reevaluated, however, with the next update. Low temperatures will make it to the 30s most areas outside the major urban areas and some immediate coastal areas. NW winds should diminish quickly in vicinity of sunset. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday should start out mostly clear with high clouds streaming in from the west during mid to late afternoon. High temperatures look to be similar to today`s values. A light gradient will set the stage for sea breezes along both east and south facing coasts on Monday. Short wave energy rotating about a long wave closed low approaching the NW Great Lakes will likely bring a baggy surface cold front or occlusion toward the area early Tue AM. Several factors gleaned from a consensus of numerical prediction models favor a high likelihood of showers with this system including divergence aloft, a near coupling of a strengthening low level jet and the right entrance region to the upper jet and precipitable waters over 1.5 inches. Anticipate showers moving into the CT River Valley soon after 06z Mon and reaching the MA east coast around 09Z Mon. Believe the moisture pooling and favorable dynamics could set the stage for some heavy showers, albeit progressive. A band or two of heavy showers could have some impact on the start of the Tuesday morning rush hour. Expect temperatures to remain nearly stationary or rise Mon night in response to cloud cover and warm advection. && .LONG TERM /TUESDAY THROUGH SUNDAY/... HIGHLIGHTS... * Seasonable temperatures expected much of the long term * Frontal system will bring showers to the area Tuesday * Quite a bit of uncertainty in the pattern for mid to late week Overview/confidence... High confidence in widespread rain fall late Monday into Tuesday as frontal system pass through. Thereafter models show low predictability and thus high uncertainty in regards to the cut-off low over the eastern half of the CONUS. GFS continues to be the more progressive solution opening up the low by late Friday into Saturday while the EC keeps the cut-off low around through the upcoming weekend. The UKMET seems to be more inline with the EC whereas the GEFS are inbetween the solutions. For now, continued with model blend until guidance becomes more inline. Tuesday...Moderate Confidence. Ahead of the FROPA, temperatures will warm into low 70s across the area. Dewpoints will be on the rise as well making it feel a bit more humid. Appears the best timing for precip will be Tuesday morning which could make way to a rough morning commute. GEFS continue to show 70-80 percent probs of over a half of an inch of rain, so confidence is increasing in widespread rainfall. Went ahead and bumped pops to categorical as all guidance is signally for rain across the area. A good pressure gradient develops behind the passing frontal system which could result in gusty winds near 25 mph. A few higher gusts are possible within the heavier rain showers as 40 kt LLJ develops over the region. Cannot rule out a rumble of thunder across the immediate south coast as there is some elevated instability. But because potential is still uncertain kept it out of the forecast for now. Wednesday and Beyond...Low Confidence. Again low confidence with this forecast as models seem to always struggle with cut-off lows. Depending on the guidance, passing frontal system on Tuesday could stall the front close enough to southern New England that passing waves rotating around cut-off could keep showers in the vicinity through the remainder of the week. Biggest question is the high pressure to the north of the region. If it will build in enough to keep the front and precip far enough south to keep the region dry. The EC thinks it will for Wed into Thursday while the GFS is more progressive keeping the high too far north bringing precip in as early as Wed. Because of the large spread in guidance will keep a slight chc of pop through the week until details and timing can be distinguished. Seasonable temperatures can be expected for this period. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence through Mon evening and moderate confidence late Mon night. Tonight...VFR expected except for isolated patches of radiationa fog in some interior valleys. Mon...VFR expected. Increasing high clouds late. Mon night...VFR through the evening with increasing high and middle clouds. Cigs and vsbys lowering to widespread MVFR with areas IFR after 06Z Mon in bands of showers moving west to east. A few wind gusts to 35 to 30 KT possible near the south and east coasts. KBOS TAF...High confidence in TAF through 00Z Tue. KBDL TAF...High confidence in TAF through 00Z Tue. Outlook /Tuesday through Friday/... Tuesday...Moderate confidence. Localized MVFR in rain on Tuesday. Gusty southerly winds near 30 kts across East coastal terminals. Wednesday into Thursday...Low confidence. Most likely VFR for much of this time, but model uncertainty could mean periods of MVFR in lower clouds and scattered showers. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Plan to let Small Craft Advisories play out as originally construed. Main issue moving into this evening will be residual rough seas as a combination of wind wave opposing a swell from Karl. The wind forcing should end by this evening, but the swell will linger into tonight across the outer waters. S to SW winds will likely frequently gust to/above 25 KT late Mon night and probably result in a new round of Small Craft Advisories. Areas of fog also likely late Mon night into early Tue AM. Outlook /Tuesday through Friday/... Tuesday...High confidence. Strong cold frontal system will approach the waters on Tuesday increasing both seas and winds. Ahead of the front southerly winds will increase close to gales with seas building near 7-8 feet as a response. Vsbys will drop within any heavy rain showers as the front passes. Low risk for a rumble of thunder across the southern waters. Wednesday and Thursday...spread in the guidance has resulted in a low confidence forecast. Could see small craft conditions on the outer waters for a time as front stalls across the waters. Passing waves could increase both seas and winds each day. Again low confidence forecast. && .CLIMATE... Record low temperatures... September 26th (last set in...) Boston ....... 34 (1879) Hartford ..... 33 (1978) Providence ... 37 (1967) Worcester .... 28 (1925) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Frost Advisory from 2 AM to 8 AM EDT Monday for MAZ002>004- 008>013-017-018-026. RI...None. MARINE...Small Craft Advisory until 3 AM EDT Monday for ANZ250-254-255. Small Craft Advisory until 5 PM EDT this afternoon for ANZ256. && $$ SYNOPSIS...KJC/Thompson NEAR TERM...Thompson SHORT TERM...Thompson LONG TERM...Dunten AVIATION...Dunten/Thompson MARINE...Dunten/Thompson CLIMATE...Staff

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