Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201359 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 959 AM EDT WED AUG 20 2014 .SYNOPSIS... MAINLY DRY WEATHER...EXCEPT MAYBE A SHOWER IN THE WEST...WITH TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL EXPECTED THROUGH THE WEEKEND. PATTERN STARTS TO BECOME A BIT MORE UNSETTLED EARLY NEXT WEEK WITH AN APPROACHING FRONT. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 AM UPDATE... PATCHY DENSE FOG HAS ALL BUT ERODED WITH DAYTIME HEATING AND BOUNDARY LAYER MIXING...THE OVERNIGHT CULPRIT BEING SURFACE MOISTURE POOLING BENEATH A DRY INVERSION IN LOCATIONS WHERE WINDS WERE LIGHT/VARIABLE AND CONDITIONS WERE CLEAR TO ALLOW FOR GOOD NOCTURNAL RADIATING. AS FOR TODAY...A DRY AND QUIET FORECAST. DRY AIR AND SUBSIDENCE PREVAILING WITH THE MID-LEVEL RIDGE SWEEPING ACROSS THE REGION. THE COMBINATION OF NEIGHBORING CLOSED LOWS OVER NE NORTH AMERICA AND A STALLED E-W FRONTAL BOUNDARY OFF THE MID-ATLANTIC RESULTS IN CONTINUED STRENGTH AND INFLUENCE OF THE LABRADOR HIGH. AIR NEEDS TO SINK SOMEWHERE BETWEEN AREAS OF CONVERGENCE. AS THE MID-LEVEL RIDGE PUSHES E LATE IN THE DAY...HEIGHTS WILL LOWER INTO THE CT-VALLEY WITH THE APPROACH OF THE H5 TROUGH AXIS AND VORTICITY. THOUGH ASCENT IS LACKING AS BETTER DYNAMICS ALONG WITH THE SURFACE WARM-FRONT RESIDE W. PERHAPS SOME INCREASING DIFFLUENCE ALOFT AND WEAK SW-ISENTROPIC UPGLIDE COULD YIELD A SPRINKLE INTO W NEW ENGLAND...THOUGH THE ABUNDANCE OF DRY AIR PER THE 12Z CHATHAM SOUNDING /PWAT OF 0.64 INCHES FOR MID-AUGUST!?/ AND INFLUENCE OF THE LABRADOR HIGH AND ATTENDANT SUBSIDENCE WILL MAKE IT DIFFICULT FOR ANY MOISTURE TO PROCEED E OF THE CT-RIVER VALLEY LET ALONE REACH THE GROUND. A WARMER AIRMASS STREAMING ACROSS THE REGION FROM THE SW COMBINED WITH A MIXING BOUNDARY LAYER UP TO H85 /+12-14C/ SHOULD ALLOW HIGHS OF AROUND THE LOW-80S /SEASONABLE/. COOLER ALONG THE SHORELINES WITH ANTICIPATED SEA-BREEZES EXPECTED AROUND LATE- MORNING. EXPECT SOME GUSTY E-WINDS BEHIND THE SEA-BREEZE AROUND 10 MPH. A FEW SITES INTO THE MID-80S WOULD NOT BE SURPRISING ACROSS THE INTERIOR. MID- TO HIGH-LEVEL CLOUDS OUT OF PA/NY MAY CURTAIL SOME OF THE DAYTIME HEATING...BUT THERE IS EVIDENCE OF ITS EROSION E...SO WILL PREVAIL WITH PARTLY CLOUDY CONDITIONS FOR AREAS MAINLY AROUND AND W OF THE WORCESTER HILLS. MOSTLY CLEAR CONDITIONS TO THE E WITH ONSHORE SEA-BREEZE AND ADVECTION OF A MARINE STABLE LAYER...ALSO THE GREATER DEEP-LAYER INFLUENCE OF DRY AIR /AGAIN...SEE THE 12Z CHATHAM SOUNDING/. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... TONIGHT... THE APPROACHING WARM FRONT AND GRADUALLY OPENING UPPER LVL CUTOFF...COMBINED WITH GRADUAL MOISTURE LOADING OF THE COLUMN IS LIKELY TO LEAD TO MORE CLOUD COVER ACROSS THE REGION THAN PREVIOUS NIGHTS. NOT OUT OF THE QUESTION A SHOWER IS ABLE TO SLIDE ACROSS THE W...BUT BOTH JET AND VORTICITY RELATED DYNAMICS ARE QUITE WEAK AND OVERALL COLUMN MOISTURE REMAINS FAIRLY LOW UNTIL THE EARLY MORNING HOURS. THEREFORE...WILL MAINTAIN A MOSTLY DRY FORECAST EXCEPT THE EXTREME WRN FRINGES OF THE BOX CWA THROUGH THE OVERNIGHT HOURS. REGARDING TEMPERATURES...GIVEN THE INCREASED MOISTURE /CLOUD COVER/ AND WARMER EVENING TEMPERATURES EXPECT THAT OVERNIGHT LOWS WILL BE WARMER THAN PREVIOUS NIGHTS IN SPITE OF THE NEAR CALM FLOW ONCE AGAIN. MORE WIDESPREAD MID 50S WITH EVEN SOME NORMAL HEAT ISLANDS HOLDING IN THE LOW-MID 60S ARE EXPECTED. THURSDAY... INVERTED RIDGING REMAINS IN PLACE...AND MAINLY E-SE FLOW EXPECTED ACROSS THE REGION. THE MARINE INFLUENCE IS LIKELY TO STAVE OFF APPROACHING WARM FRONT AS IT/S ATTENDANT UPPER LVL CUTOFF DIMINISHES TO AN OPEN WAVE WITH CUTOFF HIGH PRES TO THE N. UPPER LVL AND LOW LVL JETS ARE WEAK AND WITH OVERALL VORTICITY DECREASING...THEREFORE DYNAMIC FORCING IS RELATIVELY WEAK EVEN AS OVERALL COLUMN MOISTURE INCREASES THROUGH THE DAY /PWATS APPROACH 1.75 INCHES/. ALSO...WITH MARINE FLOW AND WARM FRONT TRAPPED TO THE W...IT/S UNLIKELY THAT THERE WILL BE MUCH DESTABILIZATION THROUGH THE DAY. GIVEN ALL OF THIS...THE THREAT FOR SHOWERY ACTIVITY REMAINS FAIRLY LOW. WILL FOCUS ONLY LOW CHANCE POPS W OF THE CT VALLEY...WITH SLIGHT CHANCE POPS INTO THE WORCESTER HILLS. CONVECTIVE ACTIVITY SHOULD DIVE TO THE SW OF THE REGION WHERE INSTABILITY AXIS RESIDES. HAVE KEPT THUNDER OUT OF THE FORECAST WITH THIS UPDATE DUE TO THE MARINE FLOW AND MODEST LAPSE RATES. THE ADDITIONAL CLOUD COVER AND MARINE FLOW ARE ALSO LIKELY TO KEEP HIGH TEMPS COOLER THAN NORMAL /MAINLY MID 70S/ DURING THE DAY THU. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... HIGHLIGHTS... * QUIET WEATHER EXPECTED THROUGH MUCH OF THE LONG TERM * UNCERTAINTY INCREASES EARLY NEXT WEEK WITH AN APPROACHING FRONT RATHER UNIQUE AND STABLE UPPER LEVEL PATTERN WILL SLOWLY BREAK DOWN LATE THIS WEEK INTO THIS WEEKEND. 20/00Z GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH THIS WEEKEND...THEN MORE DIFFERENCES APPEAR EARLY NEXT WEEK. WILL CONTINUE TO FAVOR A CONSENSUS BLEND TO SMOOTH OVER THE MORE MINOR DIFFERENCES. HIGH PRESSURE IN QUEBEC WILL KEEP THINGS RELATIVELY DRY ACROSS MOST OF SOUTHERN NEW ENGLAND THROUGH THIS WEEKEND. THERE IS POTENTIAL FOR A FEW SHOWERS ACROSS THE WESTERN HALF OF SOUTHERN NEW ENGLAND THURSDAY NIGHT IF SOME MOVING PARTS COME TOGETHER. MOISTURE IS THE MAIN LIMITING FACTOR...WITH INSTABILITY A CLOSE SECOND ONCE THE SUN SETS. THIS HIGH PRESSURE WILL SINK SOUTH THROUGH THIS WEEKEND INTO EARLY NEXT WEEK...EVENTUALLY DROPPING SOUTH OF SOUTHERN NEW ENGLAND AND RETURNING US TO A MORE WESTERLY FLOW. A LOW PRESSURE IN ONTARIO MAY EVENTUALLY MOVE EASTWARD INTO QUEBEC...SWINGING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND SOMETIME TUESDAY INTO WEDNESDAY. DEPENDING ON AVAILABLE MOISTURE...THIS FRONT MAY INITIATE A FEW SHOWERS AND THUNDERSTORMS. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM...THROUGH THURSDAY...HIGH CONFIDENCE. MAINLY VFR THROUGH THURSDAY. ONLY CAVEAT WILL BE SOME SPOTTY GROUND FOG AT TYPICALLY PRONE AIRPORTS BOTH THIS MORNING AND AGAIN LATE TONIGHT. A FEW SHOWERS POSSIBLY MAINLY W OF AN IJD-ORH-AFN LINE DURING THE DAY ON THU. FLOW SHIFTS FROM THE SW TO THE E THROUGH THE DAY TODAY...ASSISTED BY SEA BREEZES. LIGHT AND VRB FLOW RETURNS AGAIN TONIGHT...WITH E FLOW AGAIN ON THU. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY... MODERATE CONFIDENCE. MAINLY VFR. LOW PROBABILITY OF PATCHY MVFR/IFR FOG EACH NIGHT. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM...THROUGH THURSDAY...HIGH CONFIDENCE. THE MAINLY QUIET BOATING WEATHER CONTINUES. WINDS REMAIN MAINLY E TO SE WITH A FEW GUSTS AROUND 15 KT POSSIBLE ESPECIALLY ACROSS THE OUTER EDGE OF THE S AND SE WATERS. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY... MODERATE TO HIGH CONFIDENCE. QUIET BOATING WEATHER IS EXPECTED THROUGH MUCH OF THIS PERIOD WITH HIGH PRESSURE ACROSS THE REGION. LOW PROBABILITY OF PATCHY OVERNIGHT FOG LIMITING VISIBILITIES. SEAS MAY INCREASE ON THE OUTER WATERS THIS WEEKEND AS AN OCEAN STORM PASSES WELL EAST OF THE SOUTHERN NEW ENGLAND WATERS. WNA WAVE GUIDANCE LOOKS TO BE TOO HIGH BASED ON EXPECTED WINDS...LOWERED THIS GUIDANCE BY 20 PERCENT. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...BELK/DOODY NEAR TERM...SIPPRELL SHORT TERM...DOODY LONG TERM...BELK AVIATION...BELK/DOODY MARINE...BELK/DOODY

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