Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260004 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 804 PM EDT TUE AUG 25 2015 .SYNOPSIS... A COLD FRONT WILL BRING SCATTERED SHOWERS AND THUNDERSTORMS AS IT SLOWLY CROSSES SOUTHERN NEW ENGLAND TONIGHT. HIGH PRESSURE SLOWLY BUILDS IN FOR MID AND LATE WEEK WITH MAINLY DRY AND SEASONABLE WEATHER AND COMFORTABLE HUMIDITY LEVELS EXPECTED WEDNESDAY INTO SATURDAY. WARMER TEMPERATURES AND HIGHER HUMIDITIES RETURN FOR THE BEGINNING OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 735 PM UPDATE... LINE OF SLOW MOVING SHOWERS AND THUNDERSTORMS CONTINUES FROM NW WORCESTER AND EASTERN FRANKLIN COUNTIES SW THROUGH NEAR THE HARTFORD-SPRINGFIELD AREA INTO NW HARTFORD COUNTY AT 2330Z. AS THE SUN HAS SET...THREAT FOR SEVERE WEATHER HAS LOWERED. HOWEVER...CONVECTION HAS BEEN TRAINING ACROSS PORTIONS OF THE CT VALLEY AND MOVED VERY SLOWLY E OVER THE LAST FEW HOURS AHEAD OF NEARLY STATIONARY FRONT NEAR THE NEW ENGLAND/NY STATE LINE. LOW LEVEL CONVERGENCE AND HIGH DEWPTS /AROUND 70 DEGREES/ IN PLACE HELPING WITH VERY HEAVY DOWNPOURS IN SHOWERS/TSTMS. HAVE ISSUED FLOOD ADVISORIES AND WARNINGS IN THIS GENERAL AREA OVER THE LAST FEW HOURS. NOTING SOME LOW CLOUDS BEGINNING TO PUSH ONSHORE ACROSS THE MID AND OUTER CAPE AND NANTUCKET WHICH LOOK TO SHIFT CLOSE TO THE IMMEDIATE E COAST ON GENERAL S-SE WINDS. DEBRIS CLOUDS FROM THE CONVECTION TO THE W WILL PUSH SLOWLY E THROUGH MIDNIGHT OR SO. SOME QUESTION HOW FAR E THE CONVECTION WILL MOVE AS IT WEAKENS OVERNIGHT AS THE FRONT SLOWLY CROSSES. HAVE UPDATED NEAR TERM WEATHER TO SLOW THE PROGRESSION OF THE SHOWERS/TSTMS A BIT OVERNIGHT...HAVING THEM ARRIVE INTO E MA/RI UNTIL BETWEEN 06Z-08Z. BETTER ENERGY DOES EVENTUALLY LIFT NE WITH WEAK WAVE ON THE FRONT AS IT SHIFTS E. REMAINDER OF GRIDS IN DECENT SHAPE. HAVE UPDATED TO BRING CURRENT AND INCORPORATED TIMING INTO OVERNIGHT FORECAST. PREVIOUS DISCUSSION... COLD FRONT CONTINUES TO SLOWLY MOVES ACROSS SOUTHERN NEW ENGLAND...REACHING THE EAST MASS COAST TOWARD DAYBREAK. CHANCE OF SHOWERS/FEW TSTMS WILL LINGER UNTIL IT MOVES THROUGH...BUT INCOMING MID LEVEL DRY AIR WILL LIMIT THE ABILITY OF ANY SHOWER. DEW POINTS WILL REMAIN HIGH MUCH OF THE NIGHT...BUT BEGIN TO LOWER OVERNIGHT AFTER THE COLD FRONT MOVES THROUGH. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... UPPER LOW LINGERS OVER QUEBEC WITH CYCLONIC FLOW AND COLD ADVECTION ALOFT OVER NEW ENGLAND. SURFACE HIGH PRESSURE SUPPLIES SUBSIDENCE NEAR GROUND. PLENTY OF DRY AIR NEAR THE SURFACE AND A MOIST LAYER ABOVE 850 MB. EXPECT THERE WILL BE SOME CLOUDS WEDNESDAY...BUT OTHERWISE A FAIR DAY WITH MIXING REACHING UP TO 825 MB AND POSSIBLY A LITTLE HIGHER. TEMPS AT THAT LEVEL WILL SUPPORT MAX SFC TEMPS IN THE LOW TO MID 80S. DEW POINTS WILL TREND LOWER /MORE COMFORTABLE/ WITH AFTERNOON VALUES IN THE MID 50S TO AROUND 60. FAIR WEATHER CONTINUES WEDNESDAY NIGHT WITH A LIGHT NORTHWEST WIND. MIN TEMPS WILL REACH NEAR DEW POINT MOST PLACES WITH VALUES IN THE MID 50S TO LOW 60S...A LITTLE HIGHER IN BOSTON AND ALONG THE CAPE AND ISLANDS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... OVERVIEW... MEDIUM RANGE MODELS AND ENSEMBLES REMAIN IN VERY GOOD AGREEMENT DURING THE THU-SAT TIMEFRAME...WEAKENING THE EASTERN LONG WAVE TROUGHING AS CUTOFF LOW LIFTS NE OVER EASTERN CANADA. UPPER FLOW BECOMES MORE ZONAL ACROSS THE EASTERN SEABOARD BY LATE THIS WEEK. LARGE SURFACE HIGH PRESSURE WILL BE THE DOMINANT FEATURE ACROSS THE EASTERN HALF OF THE U.S. INTO THIS WEEKEND. DO NOTE DIVERGENCE IN SOME OF THE MODEL SOLUTIONS DURING THIS WEEKEND...NAMELY THE 06Z/12Z GFS...IN HANDLING LINGERING H5 SHORT WAVE WEAKNESS. MOST MODELS AND ENSEMBLES KEEP THIS HANGING AROUND THE GREAT LAKES INTO OHIO VALLEY...BUT THE GFS SHIFTS IT E MUCH FASTER AND OVERDOES THE PRECIP FIELD. ON SATURDAY...IT TRIES TO WORK MOISTURE UP THE EASTERN SEABOARD AROUND THE SUBTROPICAL RIDGE OFFSHORE...THEN SHIFTS SHORT WAVE ENERGY E AROUND THE SUNDAY/SUNDAY NIGHT TIMEFRAME. THE 00Z ECMWF/GGEM KEEP THIS WEAKNESS WELL W OF THE REGION AND NOT NEARLY AS MUCH CONVECTION WITH IT AS THE HIGH PRES OFFSHORE REMAINS IN CONTROL. GEFS/ECENS MEANS ALSO KEEP A MAINLY DRY FORECAST GOING...SO LEANED TOWARD THE DRIER SOLUTION DURING THIS TIMEFRAME. INTO EARLY NEXT WEEK...LOOKS LIKE HIGH PRES RETURNS AS W-NW FLOW ALOFT TAKES OVER WITH HIGH AMPLITUDE UPPER RIDGE BUILDING INTO HUDSON AND JAMES BAYS. SW SURFACE WINDS TAKE OVER...WHICH BRING WARMER TEMPS AND HIGHER HUMIDITY. LEANED TOWARD AVAILABLE GUIDANCE FOR THE EARLY PORTION OF THIS FORECAST...THEN TRANSITIONED TOWARD THE ENSEMBLE MEANS FROM SUNDAY ONWARD. DETAILS... THURSDAY THROUGH SATURDAY...HIGH CONFIDENCE. LARGE HIGH PRES RIDGE BUILDS E OUT OF THE MIDWEST/GREAT LAKES. EXPECT DRY CONDITIONS. A GENERAL W-NW FLOW IN PLACE FOR THURSDAY-FRIDAY...THEN RIDGE AXIS SHIFTS E ON SATURDAY BRINGING RETURN TO SW WINDS AND GRADUALLY INCREASING HUMIDITY. SUNDAY...LOW CONFIDENCE. AS MENTIONED ABOVE...MODEL SOLUTION DIVERGENCE DUE TO TIMING OF SYNOPTIC FEATURES ACROSS THE REGION. LEANED TOWARD THE HPC GUIDANCE FOR THIS PERIOD. KEPT A DRY FORECAST GOING. WILL ALSO SEE TEMPS RISE...WITH HIGHS POSSIBLY AS MUCH AS 5 TO 10 DEGREES ABOVE NORMAL. MONDAY AND TUESDAY...LOW TO MODERATE CONFIDENCE. UPPER LEVEL RIDGE BUILDS ACROSS THE CENTRAL U.S. INTO CENTRAL CANADA...KEEPING MAINLY DRY FLOW IN PLACE. SOME UNCERTAINTY DUE TO DIVERGENCE WITH EARLIER SOLUTIONS...THOUGH LOOKING A BIT MORE CONFIDENT. TEMPERATURES WILL CONTINUE TO TREND ABOVE NORMAL DURING THIS TIMEFRAME...WHICH IS BACK TO SCHOOL FOR SOME. BOTH MODELS AND ENSEMBLES ARE HINTING AT UPPER 80S TO AROUND 90 AS UPPER LEVEL RIDGE CONTINUES TO BUILD ACROSS THE CENTRAL U.S. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/... THIS AFTERNOON...MODERATE CONFIDENCE. AREAS OF IFR FOG ALONG THE MASS EAST COAST UNTIL WINDS BECOME SOUTH. OTHERWISE VFR WITH PATCHES OF MVFR CIGS IN SCATTERED SHOWERS/TSTMS...MOSTLY IN CENTRAL MASS AND NORTHEAST CT. TONIGHT...MODERATE CONFIDENCE. LINE OF SHOWERS/TSTMS ACROSS CT VALLEY REGION EARLY WITH LOCAL MVFR-IFR CONDITIONS POSSIBLE. PATCHY FOR DEVELOPING OVERNIGHT WITH MVFR AND SOME IFR. WIND SHIFT WITH COLD FRONT PASSAGE...WINDS BECOMING LIGHT WEST BY MORNING MOST AREAS. WEDNESDAY AND WEDNESDAY NIGHT...HIGH CONFIDENCE. VFR. PATCHY IFR IN FOG LATE WEDNESDAY NIGHT. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. EXPECT MAINLY VFR THOUGH SOME MVFR CIGS AND SCT SHOWERS/TSTMS MAY APPROACH AHEAD OF COLD FRONT AROUND OR AFTER 06Z THROUGH ABOUT 12Z. WIND SHIFT TO WEST AS A COLD FRONT MOVES THROUGH...AROUND 12Z-14Z. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. OUTLOOK /THURSDAY THROUGH SUNDAY/...MODERATE TO HIGH CONFIDENCE. THURSDAY THROUGH SUNDAY...MAINLY VFR CONDITIONS. COULD SEE WEAK SEA BREEZES ALONG THE COASTLINES. MAY SEE BRIEF PATCHY FOG OVERNIGHT THU NIGHT ACROSS NORMALLY PRONE INTERIOR VALLEYS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/...HIGH CONFIDENCE. WINDS AND SEAS WILL REMAIN BELOW 25 KNOTS AND 5 FEET THROUGH THE PERIOD. A COLD FRONT MOVES ACROSS SOUTHERN NEW ENGLAND TONIGHT AND MAY BRING A FEW SHOWERS TO THE WATERS...POSSIBLY A TSTM. AREAS OF FOG ON THE EASTERN MASS WATERS WILL DIMINISH WITH THE WIND SHIFT. ADDITIONAL FOG WILL AFFECT THE WATERS IN THE LIGHT FLOW TONIGHT. OUTLOOK /THURSDAY THROUGH SUNDAY/...HIGH CONFIDENCE. EXPECT WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT CRITERIA AS HIGH PRESSURE TAKES CONTROL. EXPECT W-NW WINDS THU-FRI...SHIFTING TO S-SW FRI NIGHT-SUNDAY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB/EVT SHORT TERM...WTB LONG TERM...EVT AVIATION...WTB/EVT MARINE...WTB/EVT

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