881 FXUS61 KBOX 171125 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 725 AM EDT Mon Jun 17 2019 .SYNOPSIS... A cold front that moved through Southern New England last night stalls south of the coast. Weak high pressure builds over the region, bringing us dry weather today. The stalled front will linger south of our area for much of the week. A series of disturbances moving along the front will bring rounds of showers during the week, along with embedded heavy downpours and possibly a few thunderstorms. Dry conditions may return next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 730 am update... Visible satellite and surface obs this morning show the cold front sitting south of our coast this morning, with gradually clearing skies behind. The only lingering area of fog/low clouds is Cape Cod and the islands early this morning. These should clear out through the morning, but low clouds could linger over Nantucket and waters to the south for much of the day before low clouds advance back in from the south this overnight. Light winds today under building high pressure will allow for seas breezes to take hold by early afternoon. Previous Discussion... Early morning satellite imagery shows clearing skies over Northern NY and VT/NH. This clearing is trending SE, so we expect clearing skies during the morning in Western/Central/Northeast sections, while clouds linger along the South Coast and parts of RI and SE Mass until midday. Cold front has moved through the region, with a light west- northwest wind observed at most stations. The front is becoming aligned parallel to the zonal upper flow, so we expect it to stall south of the Islands during the day. High pressure will encourage light wind, but also a shifting wind. Expect winds turning out of the east and southeast during late morning and afternoon along the coast. The developing sun will encourage some mixing, with the layer reaching to 850 mb. Temps at that level will be 10-12C, so full mixing would support max sfc temps in the upper 70s and lower 80s. On the other hand clouds associated with the stalled front may interfere with full mixing. We stayed close to existing forecasts. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... The next upper shortwave crosses the region from west to east tonight and Tuesday, with the best jet support...right entrance region...passing late tonight and Tuesday. Expect increasing POPs during this time, with highest values reached along the South Coast and lower values along the Northern Mass border. Absent a low level east flow or any above-surface southerly flow and overrunning, we are calling this showers. Stability parameters are mediocre for any thunder signal. But K index does barely reach 30 along southern parts of CT-RI-SE Mass, so we have indicated widely scattered thunder in this area Tuesday. Dew points around 60 both tonight and Tuesday. This should keep min temps 60 to 65. Little mixing depth Tuesday, but low level temps will be equiv to 850 temps of 6-8C. So the forecast sfc highs will be upper 60s to mid 70s. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Bouts of rain, embedded heavier showers, possible thunderstorms through Friday * Seasonable temperatures throughout, warming toward the weekend * Drying out Saturday/Sunday Details... Tuesday night and Wednesday... Continued unsettled pattern with quasi-zonal flow which allows a quick progression of shortwaves through the region. Stalled frontal boundary continues to linger in the vicinity laying W-E parallel to steering flow. With this front, a quasi-stationary upper jet in favorable position for synoptic lift, and precipitable water values consistently above 1", a series of weak disturbances will bring a chance of rain and isolated thunderstorms. The main lifting mechanism is a surface wave of low pressure passing to the south. Still some uncertainty on the track of this which will impact how widespread rain chances are Tuesday night and Wednesday. Not a lot of model consensus at this point so leaning toward a blend giving chance POPs throughout; highest likelihood south of the MA/CT border. Highs hover just below normal, in the 70s...cooler along the coast. Thursday and Friday... Should see a break in the rain for a time, if briefly, on Thursday between disturbances. Looking upstream a surface low which formed in the lee of the Rockies a day previous moves into the Ohio Valley, strengthening as it moves toward New England late Thursday. This being the strongest and most organized system of the week, we also see a more amplified mid level trough axis approaching, ahead of which moisture advection brings a plume of PWATs ~2". It means widespread potentially heavy rainfall and scattered thunderstorms for southern New England sometime around late Thursday/Friday. Timing details are still uncertain and will depend on exactly how Wed-Thurs plays out but by Friday night most of the rain should have moved out. Saturday and Sunday... By next weekend we finally see a pattern change as flow becomes more meridional in a western trough/eastern ridge set up. Rising heights and building surface high pressure should keep things dry and sunny. Increasing subsidence will also help temperatures warm a bit, though no major heat waves are expected for the 7 day forecast period. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Today...Lingering IFR-LIFR ceilings in far southeastern Mass for the next few hours. There is a chance that low ceilings may linger at Nantucket much of the day. VFR elsewhere. Sea breezes will develop, especially along the east Mass coast, from late morning through the afternoon. Tonight...Moderate confidence. VFR to start, then conditions lower to MVFR/IFR overnight. The South Coast will be most favorable for this, while the transition may take longer farther north. Initially it will be due to lowering ceilings. Later in the night, showers will move into the region bringing lower visibility. Best chance for showers will be along the South Coast. Tuesday...Moderate confidence. IFR ceilings CT-RI-SE Mass, MVFR ceilings to the north. Vsbys 3-5 nm in showers in the south, 5 to 10 nm in the north. Fog along the southern areas may bring vsbys to 1-2 nm at times. There is a slight chance of thunder in southern areas, mainly along the South Coast. KBOS Terminal...Moderate confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Tuesday Night through Friday/...Moderate confidence. Tuesday Night: MVFR/IFR conditions possible. Chance SHRA, patchy BR. Wednesday: MVFR/IFR conditions possible. Chance SHRA, isolated TSRA. Wednesday Night: Mainly MVFR, with areas IFR possible. Chance SHRA, isolated TSRA, patchy BR. Thursday: Mainly MVFR, with local IFR possible. SHRA likely. Thursday Night: Mainly IFR, with areas MVFR possible. SHRA likely, slight chance TSRA, patchy BR. Friday: Mainly VFR, with local IFR possible. Chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. Today... High pressure in Canada will bring light shifting winds today. Northern waters will show clearing skies, while waters south of New England will have variable sky cover. Winds will remain below 20 knots. Lingering 5 foot seas in the southern outer waters will diminish this morning. Small craft Advisory continues on the southern outer waters this morning. Tonight... Another weather disturbance approaches from the west tonight. Expect clouds to fill in again, and showers will develop later in the night. Showers and fog will lower visibility overnight. Winds and seas should remain below Small Craft criteria. Tuesday... The weather disturbance moves past Southern New England, bringing reduced visibility in showers and fog to the waters. There is also just enough instability indicated to support widely scattered thunderstorms over the waters south of Southern New England. Outside of any thunderstorms, winds should remain below 20 kt and seas below 5 feet through the day. Outlook /Tuesday Night through Friday/...Moderate confidence. Tuesday Night: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms, patchy fog. Local visibility 1 to 3 nm. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms, patchy fog. Areas of visibility 1 to 3 nm. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers, slight chance of thunderstorms, patchy fog. Local visibility 1 to 3 nm. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until noon EDT today for ANZ255-256. && $$ SYNOPSIS...WTB/BW NEAR TERM...WTB/BW SHORT TERM...WTB LONG TERM...BW AVIATION...WTB/BW MARINE...WTB/BW