Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221100 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 700 AM EDT TUE JUL 22 2014 .SYNOPSIS... SOUTHWEST FLOW WILL BRING AN INCREASE IN HEAT AND HUMIDITY TODAY...WHICH WILL PERSIST INTO WEDNESDAY. SHOWERS AND THUNDERSTORMS WILL LIKELY MOVE ACROSS THE REGION LATE WEDNESDAY AFTERNOON AND EVENING AHEAD OF A COLD FRONT. A FEW STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE. COLD FRONT SLOWLY MOVES OFFSHORE THURSDAY WITH A TREND TO IMPROVING WEATHER. HIGH PRESSURE BUILDS OVER THE REGION FRIDAY AND SATURDAY...THEN MAKES WAY FOR UNSETTLED WEATHER APPROACHING FROM THE SOUTHWEST SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 AM UPDATE... FOG LINGERS ACROSS THE OUTER CAPE AND THE ISLANDS. ALSO SOME PATCHY FOG IN PLACES SUCH AS NORWOOD AND WESTFIELD. THIS SHOULD BURN OFF SHORTLY THIS MORNING. WE HAVE MADE ONLY MINOR CHANGES TO THE EARLIER TIMING. HOURLY TEMPS AND DEWPOINTS WERE ADJUSTED A LITTLE LOWER BASED ON OBSERVED CONDITIONS...BUT NO CHANGE TO EXPECTED VALUES THIS AFTERNOON. PREVIOUS DISCUSSION... THE TWO MAIN ISSUES TODAY INVOLVE BURNING OFF OF LOW CLOUDS AND FOG AND RISK OF ANY LATE AFTERNOON CONVECTION IN THE WEST. WITH REGARD TO LOW CLOUDS AND FOG...EXPECT GRADUAL IMPROVEMENT THROUGH MID/LATE MORNING. HAVE A STRONG SUN ANGLE AT THIS TIME OF YEAR...BUT DEVELOPING SW FLOW AND GRADUALLY INCREASING DEWPOINTS WILL LIKELY SLOW THE PACE AT WHICH THE LOW CLOUDS AND FOG BURN OFF OVER THE CAPE AND NANTUCKET. CONVECTION CHANCES APPEAR TO BE VERY LIMITED THIS AFTERNOON AS MODELS DEPICT MID LEVEL CAP BECOMING ESTABLISHED. NEVERTHELESS...WILL RETAIN A SLIGHT CHANCE OVER THE EAST SLOPES OF THE BERKSHIRES WHERE SHOWALTER INDEX DROPS TO NEAR ZERO AND THE K INDEX RISES TO NEAR 30 FOR A PERIOD. ALSO...ISOLATED SHOWERS/TSTMS DEVELOPED MON AFTERNOON ACROSS NEW YORK STATE IN AN AIR MASS THAT IS SLIDING IN OUR DIRECTION.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... TONIGHT...EXPECTING TEMPERATURES TO BE 2 OR 3 DEGREES MILDER TONIGHT IN MOST LOCATIONS WITH DEWPOINTS RISING FROM THE LOW TO MID 60S. ALSO EXPECTING AREAS OF LOW CLOUDS AND FOG ALONG S COASTAL AREAS AND POSSIBLY IN A FEW INTERIOR VALLEYS. WEDNESDAY...WEATHER BECOMES MORE INTERESTING AS A COLD FRONT APPROACHES FROM THE WEST. INITIALLY A MID LEVEL CAP IS EXPECTED TO INHIBIT CONVECTION BUT THAT CAP SHOULD ERODE AS THE FRONT APPROACHES IN THE LATE AFTERNOON. SBCAPE PROJECTED TO BE 1200 TO 2000 J/KG AND MID LEVEL LAPSE RATES 6.0 TO 6.5 C/KM. A FAIRLY NOTABLE BUMP OF THE K INDICES INTO THE MID TO UPPER 30S TAKES PLACE LATE WED AFTERNOON/EVENING WHILE THE SHOWALTER INDICES DROP TO AROUND -2 TO -3. THE 0 TO 6 KM WIND SHEAR IS FAIRLY MARGINAL AT AROUND OR JUST STRONGER THAN 30 KT WITH STRONGER WIND SHEAR INDICATED NORTH OF THE FORECAST AREA PER THE 00Z GFS AND ECMWF. THE 00Z NAM RUN PROJECTED CLOSER TO 40 KT SHEAR ACROSS THE NORTHERN ZONES BUT NOT QUITE READY TO BUY THAT. AT ANY RATE...SHEAR STILL LOOKS STRONG ENOUGH COMBINED WITH THE INSTABILITY TO SUPPORT SOME STRONG TO SEVERE TSTMS TO PERHAPS AS FAR EAST AS AN ASH-LWM-BED-IJD LINE. PWATS ARE EXPECTED TO RISE TO BETWEEN 1.7 AND 2 INCHES AND SO THE RISK FOR LOCALIZED FLASH FLOODING NEEDS TO BE CONSIDERED AS WELL. HAVE PUT IN MILD ENHANCED WORDING FOR GUSTY WINDS AND HEAVY RAINFALL. WILL MENTION THE RISK OF STRONG TO SEVERE TSTMS AND LOCALIZED FLASH FLOOD RISK IN THE HWO. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... BIG PICTURE... BIG RIDGE BUILDS OVER THE ROCKIES AND PLAINS WHILE TROUGHS DIG INTO THE NORTHEAST AND THE PACIFIC NORTHWEST. UPPER RIDGE LINGERS OVER THE WESTERN ATLANTIC. FOR US...THIS WILL BRING FALLING HEIGHTS/COOLING TEMPS ALOFT THURSDAY AND FRIDAY...THEN RISING HEIGHTS/WARMING TEMPS OVER THE WEEKEND. THE PAC NORTHWEST TROUGH EJECTS OVER THE TOP OF THE ROCKIES RIDGE AND MOVES EAST. OVER THE WEEKEND IT WILL MERGE WITH THE NORTHEAST TROUGH AND PULL THE TROUGH AXIS BACK TO OUR WEST. THE ATLANTIC RIDGE REMAINS IN PLACE TO OUR EAST. THIS WILL BRING A MOIST SOUTHWEST FLOW UP OVER NEW ENGLAND SUNDAY-MONDAY. GOOD AGREEMENT AMONG MOST OF THE LONG RANGE MODELS...ALLOWING US TO USE A CONSENSUS. THE DAILIES... WEDNESDAY NIGHT-THURSDAY... THE COLD FRONT CROSSES MUCH OF OUR REGION WHILE THE RIGHT ENTRANCE REGION OF THE UPPER JET MOVES INTO POSITION OVERHEAD. WINDS AT 500 MB WILL BE 35-40 KNOTS. TOTALS NEAR 50/LI -4 AND LOWER DURING THE EARLY PART OF THE NIGHT. THE COMBINATION OF DYNAMICS AND INSTABILITY AND SHEAR SUGGEST A POTENTIAL FOR STRONG WIND GUSTS. PRECIPITABLE WATER VALUES WILL BE NEAR 2 INCHES...SO HEAVY DOWNPOURS ALSO POSSIBLE. THE COLD FRONT WILL BE JUST OFF THE SOUTH COAST AT 12Z. THE RIGHT ENTRANCE OF THE UPPER JET WILL STILL BE IN POSITION OVERHEAD. THIS MAY CAUSE A WAVE TO FORM ON THE FRONT AND KEEP SHOWERS OVER SOUTHERN/EASTERN PARTS OF SOUTHERN NEW ENGLAND THROUGH THE MORNING. BUT THE TREND DURING THE DAY WILL BE FOR IMPROVEMENT FROM NORTHWEST TO SOUTHEAST WITH AT LEAST PARTIAL CLEARING IN SOUTHERN NH AND THE CT VALLEY. TEMPS IN THE MIXED LAYER WILL SUPPORT MAX SFC TEMPS IN THE MID 70S TO AROUND 80. FRIDAY-SATURDAY... HIGH PRESSURE BUILDS OVERHEAD. SOME CONCERN THAT FRIDAY WOULD FEATURE MORE CLOUDS DURING THE DAY. THE UPPER TROUGH AXIS AND COOLER TEMPS ALOFT WILL MOVE OVERHEAD AT THIS TIME WITH SOME INCREASE IN CLOUD LEVEL MOISTURE. WITH THIS IN MIND WE HAVE INCREASE FRIDAY SKY COVER. THEN ON SATURDAY THE UPPER FLOW STARTS TO SHIFT TO SOUTHWEST WITH AN INCREASING IN HIGH CLOUDS. OVERALL A COUPLE OF FAIR DAYS WITH TEMPS AT SEASONABLE LEVELS OR A LITTLE BELOW. SUNDAY-MONDAY... AS THE UPPER FLOW RE-ESTABLISHES AS SOUTHWEST AND AIMED UP THE COAST...A SHORTWAVE MOVES INTO THE FLOW. THIS HAS THE POTENTIAL TO DEVELOP A COASTAL LOW THAT MOVES OUR WAY AND SPREADS CLOUDS AND RAIN OUR WAY ESPECIALLY FOR SUNDAY NIGHT/MONDAY. GIVEN HOW FAR OUT THIS IS...DAY 6/DAY 7...WE WILL SHOW CHANCE POPS DEVELOPING SUNDAY AND CONTINUING MONDAY. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/... GENERALLY MODERATE CONFIDENCE ON FORECAST. AREAS OF IFR CIGS/VSBYS CAPE AND NANTUCKET AND PATCHY IFR VSBYS IN FOG ACROSS THE INTERIOR. THE LOW CLOUDS AND FOG SHOULD GRADUALLY BURN OFF THIS MORNING AND THEN REAPPEAR ALONG THE SOUTH COAST AGAIN TONIGHT. OTHERWISE...VFR CONDITIONS ARE EXPECTED THROUGH WED MID AFTERNOON. DURING LATE WED AFTERNOON...MVFR CIGS AND VSBYS IN VICINITY OF SCT TSTMS AHEAD OF A COLD FRONT. A FEW TSTMS MAY BRIEFLY LOWER CIGS/VSBYS TO IFR LEVELS. ALSO...A FEW TSTMS MAY PRODUCE STRONG WIND GUSTS...ESPECIALLY NW OF AN ASH-LWM-BED-IJD LINE. KBOS TAF...MODERATE TO HIGH CONFIDENCE. GENERALLY VFR CONDITIONS EXPECTED THROUGH MOST OF WED...ALTHOUG AREAS OF FOG COULD REDUCE VSBY TO 5 TO 6 MI FOR A SHORT TIME TONIGHT. THERE WILL BE A RISK OF TSTMS APPROACHING THE FIELD AFTER ABOUT 23Z WED. KBDL TAF...HIGH CONFIDENCE IN TAF. VFR CONDITIONS EXPECTED TO AT LEAST MID AFTERNOON WED...EXCEPT FOR A LOW PROBABILITY OF MVFR CIGS/VSBYS IN STRATUS/FOG TONIGHT. THERE WILL BE A RISK OF TSTMS IN THE VICINITY OF THE AIRFIELD SOMETIME AFTER ABOUT 20Z WED. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY...MODERATE CONFIDENCE WEDNESDAY NIGHT-THURSDAY... MAINLY VFR. COLD FRONT CROSSES THE REGION WITH PERIOD OF MVFR CIGS/VSBYS IN SHOWERS/TSTMS. PATCHY IFR IN FOG...MAINLY SOUTH COAST AND ISLANDS. FRIDAY-SATURDAY...VFR.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY/...MODERATE CONFIDENCE. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH TONIGHT. THE SW FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT ON WED WITH A RISK OF GUSTS APPROACHING 25 KT. AREAS OF FOG WILL GRADUALLY BURN OFF THIS MORNING BUT MAY REDEVELOP ALONG THE SOUTH COASTAL WATERS TONIGHT. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY...MODERATE CONFIDENCE. WEDNESDAY NIGHT-THURSDAY... A COLD FRONT CROSSES THE WATERS LATE AT NIGHT AND DURING THURSDAY. GUSTY SOUTHWEST WINDS LEADING THE FRONT MAY APPROACH 25 KNOTS AT TIMES WEDNESDAY NIGHT. WINDS SHIFT TO NORTH AND NORTHEAST ON THURSDAY. SHOWERS AND SCATTERED THUNDERSTORMS WITH STRONG WIND GUSTS AND BRIEFLY HEAVY RAIN. SEAS REMAIN BELOW 5 FEET...BUT BRIEFLY HIGHER SEAS POSSIBLE IN ANY THUNDERSTORMS. FRIDAY-SATURDAY... NORTH WINDS SHIFT TO SOUTHWEST WITH SPEEDS 15 KNOTS OR LESS. SEAS REMAIN LESS THAN 5 FEET. && .EQUIPMENT...
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KBOX RADAR IS IN STANDBY MODE TODAY WHILE CONSTRUCTION TAKES PLACE NEARBY. THE RADAR WILL RETURN TO SERVICE WHEN CONSTRUCTION ENDS FOR THE DAY.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/THOMPSON NEAR TERM...WTB/THOMPSON SHORT TERM...THOMPSON LONG TERM...WTB AVIATION...WTB/THOMPSON MARINE...WTB/THOMPSON EQUIPMENT...

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