Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261057 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 657 AM EDT SUN JUL 26 2015 .SYNOPSIS... SCATTERED STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE AGAIN TODAY INTO THIS EVENING. WARM AND UNSETTLED WEATHER IS EXPECTED MONDAY AND TUESDAY WITH A CHANCE OF MAINLY DIURNAL SHOWERS AND THUNDERSTORMS. IT WILL BECOME HOT AND MORE HUMID WEDNESDAY AND THURSDAY WITH HIGHS REACHING THE LOWER TO MID 90S AWAY FROM THE COAST. A COLD FRONT MAY BRING SCATTERED THUNDERSTORMS LATE THURSDAY AND THURSDAY NIGHT. WARM AND DRY WEATHER IS EXPECTED FRIDAY INTO NEXT WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 655 AM UPDATE...A BAND OF SHOWERS AND THUNDERSTORMS WAS MOVING INTO WESTERN MA AND WESTERN CT. HAVE NOTED SOME FLEETING ROTATIONAL SIGNATURES ON DOPPLER RADAR SOUTH OF ALBANY. HELICITY VALUES ARE HIGH OVER SOUTHERN NEW ENGLAND RIGHT NOW BUT THERE IS NO CAPE WHATSOEVER. THERE IS AN AREA OF 1000 SURFACE- BASED CAPE JUST SOUTH OF WESTERN LONG ISLAND WHICH IS POISED TO SPREAD NORTHWARD LATER THIS MORNING. SPC SREF SEVERE WX PARAMETERS ARE HIGHLIGHTING THE MERRIMACK VALLEY AROUND 18Z FOR THE GREATEST POTENTIAL FOR ANY SUPERCELLULAR STRUCTURES. WIND FIELDS BECOME QUITE WEAK ALOFT THIS AFTERNOON...WHICH WOULD DIMINISH SEVERE POTENTIAL BUT WITH STRONG CAPE THERE COULD BE A LOT OF LIGHTNING AND HEAVY DOWNPOURS. STAY TUNED. PREVIOUS DISCUSSION... INTO THE MORNING... WARM FRONT ALONG THE LEADING EDGE OF A NOSE OF WARM / HIGH THETA-E AIR IS PUSHING E ACROSS THE NE-CONUS. STRONG CONVERGENCE AND DECENT FORCING NOT OUT OF THE QUESTION IN AN ENVIRONMENT OF NOTEWORTHY 0-1/0-3 KM HELICITY AS E/SE-FLOW WITHIN THE LOW-LEVELS MEETS UP WITH PREDOMINANT W-FLOW ALOFT. BUT IT APPEARS BETTER INSTABILITY LAGS PER SPC MESOANALYSIS AS THE BULK OF THUNDERSTORMS HAS HELD WELL TO THE W. NEVERTHELESS MUCH OF THE ENVIRONMENT LOOKS TO TRANSLATE E SO ALL POTENTIAL FACTORS NEED TO BE TAKEN INTO CONSIDERATION. A LIKELY EXPECTATION OF WET WEATHER TO PUSH E THOUGH THE OUTER EDGE MAY FACE SOME WEAKENING / EROSION UP AGAINST THE DRIER AND SUBSIDING AIRMASS TO THE E...SEE 0Z SOUNDINGS OUT OF GRAY AND CARIBOU MAINE. NEVERTHELESS FEEL THE STRONG FORCING ALONG THE WARM FRONT SHOULD PUSH RAIN INTO THE AREA BY MORNING WITH EMBEDDED HEAVIER SHOWERS...PERHAPS SOME THUNDERSTORMS. FEEL THE S-FLANK OF THE LINE IS BEING FED BY BETTER THETA-E AND INSTABILITY. PERHAPS THE AFOREMENTIONED RIDGING AND DRY AIR TO THE E IS NOTEWORTHY... BUT NOT THINKING IT IS GOING TO BE ENOUGH TO STOP THE TRAIN. FORECAST WAS A BLEND OF HRRR/SREF BLENDS WITH MOS GUIDANCE. STRAYED FROM EXPLICIT NAM/WRF MODEL SOLUTIONS. LIKELY POPS ACCORDINGLY. TODAY... MID-LEVEL IMPULSE AND ACCOMPANYING WARM-FRONTAL BOUNDARY LIFT N/E INTO MAINE. LOW- TO MID-LEVEL FORCING ALONG THE NOSE OF HIGH THETA-E AIR WILL CONTINUE RESULTING IN LIKELY WET-WEATHER IN THE FORM OF WIDESPREAD SHOWERS AND PERHAPS SOME THUNDERSTORMS ACROSS MUCH OF S NEW ENGLAND. A CONTINUED HIGH SHEAR / LOW INSTABILITY ENVIRONMENT. FOCUS TURNS TO THE W FOR THE MIDDAY INTO AFTERNOON PERIOD. LAGGING CONVERGENT BOUNDARY SW-NE PARENT TO A WEAK LOW- TO MID-LEVEL TROUGH. HIGH THETA-E / THERMAL AXIS FROM THE SW ACROSS THE INTERIOR ALONG AND AHEAD. APPEARING AS A HIGH INSTABILITY / LOW SHEAR EVENT WITH INSTABILITY VALUES AROUND 1-2K J/KG. CONSIDERING TRIGGERS OF LOW- LEVEL CONVERGENCE / OROGRAPHIC INFLUENCES / DESTABILIZATION WITH A PWAT ENVIRONMENT AROUND 1.25-1.50 INCHES WITH A WESTERLY MEAN-WIND OF AROUND 15 KTS...LOOKING AT THREATS OF LARGE HAIL / HEAVY RAIN / STRONG TO DAMAGING WINDS. FOCUS IS MAINLY OVER THE N/W/CENTRAL-AREAS OF S NEW ENGLAND WHERE CLOUD DEBRIS LOOKS TO CLEAR ALLOWING STORM DEVELOPMENT. CAN NOT RULE OUT SOME LOCALIZED FLOODING. GAINING A MEASURE OF CONFIDENCE...SREF PROBABILITY GUIDANCE HIGHLIGHTS THE LIKELIHOOD OF INSTABILITY OVER W NEW ENGLAND SEPARATED FROM HIGH-VALUES OF EFFECTIVE BULK SHEAR TO THE E AND OFFSHORE. CONVECTIVE OUTCOMES WITH A LEVEL OF SEVERITY APPEAR LIKELY. SO WILL GO WITH MORNING WIDESPREAD RAIN WITH EMBEDDED HEAVY SHOWERS WITH LESSER WORDING CONCERNING THUNDERSTORMS SWEEPING S NEW ENGLAND AND LIFTING OUT OF THE REGION TOWARDS MIDDAY. TO THE W THERE IS AN OPPORTUNITY FOR DESTABILIZATION ALONG A CONVERGENT BOUNDARY YIELDING A LINE OF THUNDERSTORMS TO DEVELOP THAT SHOULD PROGRESS E/SE. THERE IS THE POTENTIAL FOR SUCH STORMS TO BE STRONG TO SEVERE WITHIN A WEAK TO MODERATE SHEAR GRADIENT W TO E IN AN ENVIRONMENT OF DEEP- LAYER THIN TO MODEST CAPE AS DERIVED FROM SREF PROBABILITIES. MUGGY AIRMASS IN PLACE WITH ONSHORE S-FLOW AS HIGHS WARM INTO THE UPPER-70S TO LOW-80S. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... TONIGHT.... SCATTERED SHOWER / THUNDERSTORM ACTIVITY SHIFTING E/SE WITH THE MEAN WIND IN A CONTINUED ZONE OF LOW-LEVEL CONVERGENCE / LOWER PRESSURE. WITH DAYTIME HEATING ABSENT...STORMS SHOULD BE ON A DOWNWARD TREND. NO MORE FUEL TO THE FIRE. CONVECTIVE THREATS MAY LINGER INTO THE EVENING HOURS BUT SHOULD TRANSLATE INTO LIGHT SHOWERY WEATHER FOR THE OVERNIGHT PERIOD. OTHERWISE SOME CONCERN AS TO PATCHY DENSE FOG. EXPECT CLOUDS TO LINGER WITH MODEST S-WINDS...BUT COULD BE SOME CHANCES OVER N-PORTIONS OF S NEW ENGLAND WHERE CLEARING IS POSSIBLE UNDER LIGHT WINDS. LOWS IN THE 60S. MONDAY... LOWER PRESSURE ACROSS THE NE-CONUS ORIENTED WITH A THERMAL / THETA-E AXIS FROM THE SW CONTINUES. ANOTHER HIGH INSTABILITY/LOW-SHEAR SETUP IS ANTICIPATED. AIRMASS SHOWERS/THUNDERSTORMS ARE EXPECTED WHEREVER THE ATMOSPHERE DESTABILIZES AND/OR THERE IS LOCALIZED CONVERGENCE. BOUNDARY IS LESS DEFINED SO NOT THINKING AS SCATTERED TO WIDESPREAD AS TODAY BUT RATHER ISOLATED TO SCATTERED. WITH THE MEAN WIND FLOW AROUND 10 MPH OUT OF THE W...THREATS CONSIDERED ARE HEAVY RAIN / LARGE HAIL / PERHAPS STRONG TO DAMAGING WINDS AS STORM-CORES DROP OUT DUE TO THE WEAK-SHEAR ENVIRONMENT /POOR UPDRAFT MAINTENANCE/. WILL NEED TO MONITOR FOR ADDITIONAL STORM DEVELOPMENT ALONG ANY COLD POOLS AS STORMS POTENTIALLY DROP OUT AS WELL AS ALONG HIGH TERRAIN. ALSO POTENTIAL LOCALIZED FLOODING. HIGHS INTO THE THE MID- TO UPPER- 80S AWAY FROM THE COAST BENEATH THE WARM AND MUGGY AIRMASS. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... HIGHLIGHTS... * VERY WARM WITH SCATTERED THUNDERSTORMS STILL POSSIBLE TUESDAY. * HOT WEDNESDAY AND THURSDAY WITH HIGHS IN THE LOWER TO MID 90S. * SCATTERED STORMS POSSIBLE LATE THURSDAY AND THURSDAY NIGHT. MONDAY NIGHT...ANY CONVECTION SHOULD SLOWLY DIMINISH IN THE EVENING. OTHERWISE...A PARTLY CLOUDY AND MUGGY NIGHT WITH PATCHY FOG. TUESDAY...FOR SEVERAL DAYS WE HAVE BEEN ADVERSTISING THE BEGINNING OF A HEAT WAVE WITH DRY CONDITIONS. THE HEAT PART IS STILL ON TRACK...WITH 925 MB TEMPS RISING TO +23C AND HIGH TEMPERATURES NEARING 90 ESPECIALLY IN THE CT VALLEY. HOWEVER...NOT SO SURE ABOUT THE DRY CONDITIONS ANYMORE. THE PESKY REMNANTS OF THE TROUGH/FRONT ARE STILL HANGING AROUND THE REGION. GFS SHOWS MID LEVEL LAPSE RATES STILL IN THE 6.5C/KM RANGE...INDICATIVE OF AN EML. ITS TOTAL TOTALS INDEX REACHES 50-53 IN RI AND CENTRAL/EASTERN MA. HELICITY IS NOTEWORTHY TOO IN EASTERN MA. SFC BASED CAPE IS ON THE ORDER OF 1000- 1500 J/KG. SO...THINK WE WILL POP SCATTERED THUNDERSTORMS... ESPECIALLY IN THE I-95/495 CORRIDOR DURING THE AFTERNOON/EARLY EVENING. 00Z ECMWF MODEL RUN ALSO HINTS AT THE POSSIBILITY OF AFTERNOON CONVECTION WITH A SMALL MAX AREA OF 0.18 INCHES OF RAIN IN EASTERN MA TUE AFTERNOON. ANY CONVECTION SHOULD DIMINISH AT NIGHT WITH ANOTHER MUGGY NIGHT IN STORE. WEDNESDAY...THE UPPER LEVEL RIDGE IN THE OHIO VALLEY NUDGES EASTWARD SOME MORE AND 925 MB TEMPS WARM TO +27-28C. WITH A GOOD DEAL OF SUNSHINE AND DOWNSLOPING WESTERLY WINDS ALOFT...HIGH TEMPERATURES SHOULD SOAR INTO THE 90S. WED COULD BE THE HOTTEST DAY OF THE WEEK. WE ARE BECOMING MORE CAPPED ALOFT AND THUS CONVECTION IS NOT REALLY EXPECTED. YET...THERE IS ALWAYS A POTENTIAL FLY IN THE OINTMENT. LOW PRESSURE TO OUR NORTHEAST...OVER NOVA SCOTIA...COULD BE CLOSE ENOUGH TO DRAG A POTENTIAL BACKDOOR TYPE OF FRONT ACROSS CAPE ANN RESULTING IN WINDS SHIFTING TO THE NORTHEAST AND TEMPERATURES DROPPING INTO THE 70S. WE ARE NOT FORECASTING THIS AS YET...BUT KEEPING AN EYE ON THIS POTENTIAL. WED NIGHT SHOULD BE WARM AND STEAMY. THURSDAY...AFTER A WARM NIGHT...TEMPERATURES AGAIN SHOULD SOAR WELL INTO THE 90S BY LATE MORNING BEFORE CLOUDS INCREASE DURING THE DAY. UPPER LEVEL RIDGE IS OVERHEAD AND 925 MB TEMPS AGAIN NEAR +28C. 700 MB TEMPS OF +10C TO +11C SHOULD EFFECTIVELY CAP CONVECTION THROUGH MOST OF THE DAY. HOWEVER... NOTHING IS SIMPLE. BOTH THE GFS AND ECMWF HAVE SPED UP THE PROGRESS OF A SIGNIFICANT COLD FRONT. LATE IN THE AFTERNOON AND EVENING...SOUTHERN NEW ENGLAND COULD BE IN THE RIGHT REAR QUADRANT OF A 70-75 KNOT JET MAX AT 300 MB. THE FRONT COULD PACK ENOUGH PUNCH TO CREATE ENOUGH LIFT TO OVERCOME THE CAP IN THE EVENING HOURS. THE GFS SHOWS ROBUST K INDEX VALUES OF 38-40 INDICATING VERY MOIST AND UNSTABLE AIR. IT IS ALL A MATTER OF WHETHER THE CAP CAN BE BROKEN. FOR NOW...WILL FORECAST SCATTERED THUNDERSTORMS IN THE EVENING INTO THE NIGHTTIME HOURS. FRIDAY AND SATURDAY... LOOKS LIKE A DRY PERIOD...WITH WEAK PRESSURE PATTERNS IN PLACE OVER THE REGION. TEMPERATURES SHOULD NOT BE AS HOT AS THE MIDDLE OF THE WEEK. BUT 925 MB TEMPS ARE STILL 23-26C AND THUS HIGH TEMPERATURES IN THE 85-90 RANGE ARE POSSIBLE. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH MONDAY/... TOWARDS 12Z... RAIN PUSHES E INTO W NEW ENGLAND WITH MAINLY EMBEDDED +RA... POSSIBLE TSRA. TEMPO MVFR-IFR POSSIBLE WITH +RA. SE-WINDS. PATCHY DENSE FOG SHOULD ERODE. LOW-END VFR CIGS EXPECT ACK WHERE PERHAPS IFR HOLDS. TODAY... RAIN LIFTS N/E THROUGH MIDDAY WITH EMBEDDED +RA/TSRA AND TEMPO MVFR- IFR IMPACTS. LOW-END VFR PREVAILS THOUGH BRIEF. SHRA/TSRA DEVELOP TO THE W...SOME POSSIBLY STRONG TO SEVERE. HAIL / WINDS / LIGHTNING. AWW/S MAY BE NEEDED. INCREASING S-WINDS. TONIGHT... SHRA/TSRA MAINLY W DISSIPATE AS THEY DRIFT S/E TOWARDS THE COAST DURING THE EVENING HRS. -SHRA OVERNIGHT. CONTINUED S-WINDS WITH POSSIBLE PATCHY IFR-LIFR DENSE FOG IN SPOTS MONDAY... IMPROVING LOW-END VFR. SCT SHRA/TSRA DEVELOPING ACROSS THE INTERIOR SOME OF WHICH MAY BE STRONG TO SEVERE WITH TEMPO MVFR-IFR IMPACTS. HAIL / WINDS / LIGHTNING. AWW/S MAY BE NEEDED. BREEZY S /SW-WINDS. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. LOW-END VFR CIGS. PERHAPS SOME TEMPO MVFR WITH RAIN PUSHING THRU DURING MIDDAY. FEEL BETTER SHRA/TSRA MAY HOLD W OF TERMINAL DURING AFTERNOON. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. LOW-END VFR WITH RAIN THIS MORNING EXITING BY MIDDAY. AFTERNOON PROGGED WITH SCT SHRA/TSRA THOUGH UNCERTAIN IF DIRECT IMPACT. OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/... MON NIGHT THROUGH TUE NIGHT...MODERATE CONFIDENCE. A WEAK TROUGH OF LOW PRESSURE WILL REMAIN PARKED SOMEWHERE OVER SOUTHERN NEW ENGLAND. THERE IS A CHANCE OF MAINLY DIURNAL SHOWERS/THUNDERSTORMS WHICH WOULD HAVE LOCAL MVFR CONDITIONS. OTHERWISE MAINLY VFR DURING THE DAY. MVFR/IFR IN LOCALIZED FOG POSSIBLE AT TYPICALLY PRONE AIRPORTS LATE EACH NIGHT. WED THROUGH THU MORNING...HIGH CONFIDENCE. MAINLY VFR WITH SOME HAZE POSSIBLE. WEAK HIGH PRESSURE. THU AFTERNOON AND THU NIGHT...MODERATE CONFIDENCE. MVFR IN SCATTERED STRONG THUNDERSTORMS AS A COLD FRONT MOVES ACROSS THE REGION. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH MONDAY/...HIGH CONFIDENCE. TODAY... PERIODS OF WET-WEATHER WITH THE POSSIBILITY OF THUNDERSTORMS BY AFTERNOON CLOSER TO THE S-WATERS. SE-WINDS VEERING S WITH GUSTS UP TO AROUND 20 KTS. SEAS REMAINING BELOW 4-FEET. TONIGHT... WET-WEATHER CHANCES CONTINUING WITH THUNDER POTENTIAL DIMINISHING THROUGH THE EVENING HOURS. S-WINDS CONTINUING WITH THE POTENTIAL FOR GUSTS UP AROUND 20 KTS. SEAS BELOW 4-FEET. MONDAY... WET-WEATHER MAY HOLD MORE ACROSS THE INTERIOR THAN OVER THE WATERS AS BREEZY S-WINDS CONTINUE WITH THE POTENTIAL FOR GUSTS UP 15 KTS. SEAS REMAINING BELOW 4-FEET THE HIGHEST OF WHICH ARE ANTICIPATED OVER THE E/NE-WATERS. OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/... MON NIGHT THROUGH TUE NIGHT...HIGH CONFIDENCE. WINDS AND SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS. NEARSHORE WATERS SURROUNDING CAPE COD/ISLANDS MAY APPROACH 20 KT OUT OF THE SW. AN OCCASIONAL SHOWER OR THUNDERSTORM IS POSSIBLE WITH LOCALLY ROUGH CONDITIONS...BUT THIS THREAT SHOULD DROP BY TUE NIGHT. WED...HIGH CONFIDENCE. WINDS AND SEAS BELOW SCA THRESHOLDS. WED NIGHT AND THU...MODERATE CONFIDENCE. SOUTHWEST WINDS MAY GUST UP TO 20 KT AHEAD OF AN APPROACHING COLD FRONT. 5 TO 6 FT SWELLS ARE FORECAST FOR THE SOUTHERN OUTER WATERS BY LATE WED NIGHT AND ON THU. THERE IS A CHANCE OF REDUCED VISIBILITIES IN SCATTERED STRONG THUNDERSTORMS LATE THU AFTERNOON AND ESPECIALLY THU NIGHT IN ASSOCIATION WITH THE COLD FRONTAL PASSAGE. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...SIPPRELL/GAF NEAR TERM...FIELD/SIPPRELL SHORT TERM...SIPPRELL LONG TERM...FIELD AVIATION...SIPPRELL/FIELD MARINE...SIPPRELL/FIELD

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