Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191912 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 312 PM EDT SAT JUL 19 2014 .SYNOPSIS...
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LOW PRESSURE LIFTING NORTHEAST FROM THE MID-ATLANTIC WILL BRING MOSTLY CLOUDY CONDITIONS ACROSS MUCH OF NEW ENGLAND WITH LIGHT SHOWERS FOR THE IMMEDIATE SOUTH- AND SOUTHEAST-COASTLINE THROUGH LATE SUNDAY. THEREAFTER HIGH PRESSURE BUILDS INTO THE REGION BRINGING WITH IT DRY WEATHER ALONG WITH WARM AND HUMID CONDITIONS THROUGH MIDWEEK. A COLD FRONT FROM CANADA TRACKS THROUGH SOUTHERN NEW ENGLAND DURING THURSDAY...WITH HIGH PRESSURE RETURNING ON FRIDAY.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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REST OF TODAY... MID-LEVEL TROUGH CONTINUES TO LIFT THROUGH THE E GREAT LAKES WHILE INVIGORATING ENERGY OFF THE MID-ATLANTIC AND ACROSS THE ADJACENT STALLED FRONTAL BOUNDARY. SUBSEQUENT SW BROAD ISENTROPIC FLOW IS LENDING TO BROKEN-OVERCAST HIGH CLOUDS OVER NEW ENGLAND LIMITING ABUNDANT SUNSHINE AND KEEPING CONDITIONS SLIGHTLY COOLER WITH HIGHS AROUND THE MID- TO UPPER-70S. WHILE LOCAL RADAR IS INDICATING SOME MINOR RETURNS...MUCH OF THIS ENERGY IS SUBSEQUENT TO INCREASING MOISTURE CONVERGENCE AT THE MID- TO UPPER-LEVELS AHEAD OF THE E GREAT LAKES TROUGH WITH NONE OF THE RESULTANT ACTIVITY REACHING THE GROUND DUE TO ABUNDANT DRY AIR ASSOCIATED WITH LINGERING STRONG HIGH PRESSURE OVER THE REGION. THE FORECAST INTO THIS EVENING SHOULD REMAIN DRY. TONIGHT... OPEN-WAVE IMPULSE OVER THE GREAT LAKES AMPLIFIES AN AREA OF LOW PRESSURE ALONG A STALLED FRONTAL BOUNDARY ACROSS THE MID-ATLANTIC. EVOLVING TOWARDS AREAS OF LOWER HEIGHTS SUCCINCT WITH TROUGHING OVER THE NE CONUS...THE WAVE LOW LIFTS THE FRONT N/W CLOSER TO S NEW ENGLAND. NOTING LOW-LEVEL FRONTAL CONVERGENCE COUPLED WITH A WEAK RRQ OF THE UPPER-LEVEL JET...ENOUGH LIFT IS PRESENT ALONG WITH ISENTROPIC ASCENT TO RESULT IN OVER-RUNNING SHOWER ACTIVITY N OF THE FRONT TO DRIFT ACROSS THE S/SE SHORELINE OF NEW ENGLAND. YET A STRONGER DISTURBANCE OVER CENTRAL CANADA SUBSEQUENTLY RESULTS IN AMPLIFIED HIGH PRESSURE BETWEEN THE TWO SYSTEMS MAINLY ACROSS NEW ENGLAND. IT IS A BATTLE OF AIRMASSES AND...AS POINTED OUT BY THE PREVIOUS FORECASTER...A QUESTION OF HOW CLOSE THE LOW WILL GET TO S NEW ENGLAND. WILL GO WITH CHANCE POPS FOR IMMEDIATE S/SE COASTAL COMMUNITIES OVERNIGHT. RIDGE WILL KEEP MOST PLACES DRY. MOSTLY CLOUDY FOR THOSE AREAS AS WELL WITH MILDER LOWS AROUND THE LOW-60S...LESSER N/W WITH LOWS INTO THE MID-50S. BASED ON MODEL CONSENSUS...THE SURFACE LOW IS S OF NEW ENGLAND AND E OF DELAWARE WITH SHOWERS MAINLY CONFINED ALONG THE IMMEDIATE S-COAST.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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SUNDAY... MID-LEVEL IMPULSE AND ATTENDANT WAVE LOW TRANSLATE NE PAST 40N/70W AND WELL E OF NANTUCKET THROUGH THE DAY. THROUGH THE RIDGE HOLDS OVER INTERIOR NEW ENGLAND...OVER-RUNNING PROCESSES PREVAIL ALONG THE NE-QUADRANT OF THE SURFACE LOW CONTINUING POP CHANCES FOR THE S/SE- COASTAL COMMUNITIES. CONTINUING TRENDS OF THE WORST WEATHER AND OVERCAST CLOUD CONDITIONS FOR THE S/E WHEREAS BETTER CONDITIONS AND GREATER CHANCES OF SUNSHINE N/W. SHOULD SEE THE MAJORITY OF THE IMPACTS DURING THE EARLY-HALF OF THE DAY PERHAPS LINGERING ON INTO MIDDAY...WITH IMPROVEMENT W-TO-E TOWARDS THE LATER-HALF AS THE SURFACE LOW EXITS E. COOLER AIRMASS SIMILAR TO TODAY /SATURDAY/ STILL IN PLACE. COUPLED WITH CLOUDS AND AN INCREASE IN ONSHORE FLOW OFF THE GULF OF MAINE... EXPECT HIGHS TO BE ROUGHLY 5-DEGREE LOWER THAN NORMAL FOR THIS TIME OF YEAR WITH VALUES AROUND THE UPPER-70S /WARMEST CONDITIONS LIKELY FOR THE CT-RIVER VALLEY WHEREAS COOLEST ALONG THE E-SHORELINE/. SUNDAY NIGHT... MID-LEVEL TROUGH WITH ACCOMPANYING LOW LIFT NE INTO NOVA SCOTIA. SHOULD SEE THE RETURN OF HIGH PRESSURE DESPITE SOME LINGERING INFLUENCE OF THE TROUGH ACROSS THE EASTERN GREAT LAKES DOWN THROUGH THE OH-RIVER VALLEY. ANTICIPATED LIGHT WINDS AND CLEARING CONDITIONS COULD MAKE FOR AN OVERNIGHT PERIOD OF EFFECTIVE RADIATIONAL COOLING. WILL FORECAST LOWS AROUND THE LOW- TO MID-50S.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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HIGHLIGHTS... * DRY TO START THE WORK WEEK. * BECOMING WARMER AND MORE HUMID THROUGH MID WEEK. * BEST CHANCE OF SHOWERS AND THUNDERSTORMS IN THE WEDNESDAY TO THURSDAY NIGHT TIMEFRAME WITH THE APPROACH AND PASSAGE OF A COLD FRONT. DETAILS... MON... SURFACE HIGH PRESSURE LOOKS TO BE IN CONTROL ACROSS SOUTHERN NEW ENGLAND DURING MONDAY. WITH A MID LEVEL CAP IN PLACE EXPECT SOME DIURNAL CUMULUS BUT CHANCE FOR SHOWERS WILL BE VERY LOW. ONSHORE FLOW NEAR COASTAL LOCALES WILL KEEP MAX TEMPS ON THE COOL SIDE... 70S...WITH MAX TEMPS IN THE LOW 80S LIKELY TO BE FOUND OVER PORTIONS OF THE INTERIOR. THERE IS A CHANCE OF DEVELOPMENT OF PATCHY STRATUS/FOG MONDAY NIGHT. TUE... DURING TUE STARTING OFF WITH SURFACE HIGH PRESSURE OVER THE AREA WHICH SLIDES OFFSHORE DURING THE DAY...MEANWHILE LARGE UPPER RIDGE IN THE CENTRAL/WESTERN U.S. BUILDS SOMEWHAT INTO OUR AREA. THIS WILL RESULT IN INCREASING HEAT AND HUMIDITY. HOWEVER WITH MODELS SHOWING THE POTENTIAL FOR A MID LEVEL CAP CONVECTION SHOULD BE DIFFICULT TO ACHIEVE. CONTINUE PREV FORECAST W/MAINLY DRY FORECAST. H85 TEMPS ON TUE AROUND +18C...SO WITH ENOUGH SUNSHINE AND MIXING TEMPS ARE LIKELY TO APPROACH 90F IN SPOTS. LOW LEVEL SW FLOW SHOULD BE FAIRLY WEAK...SO THERE IS THE POTENTIAL FOR SEABREEZE DEVELOPMENT. PATCHY STRATUS/FOG MAY AGAIN DEVELOP TUESDAY NIGHT. WED INTO THU... CONTINUED INCREASE IN MOISTURE AS SW FLOW DEVELOPS OVER SOUTHERN NEW ENGLAND...AHEAD OF AN APPROACHING COLD FRONT AND POSSIBLE OPEN WAVE ALONG THE FRONT. AIRMASS BECOMES UNSTABLE...HOWEVER FRONT OR FOCUS FOR LIFT NOT QUITE INTO OUR AREA YET ON WED...SO GENERALLY SLIGHT CHANCE POPS FOR CONVECTION LOOK GOOD FOR THAT TIMEFRAME. H85 TEMPS ON WED AROUND +19C...SO WITH ENOUGH SUNSHINE AND MIXING TEMPS ARE LIKELY TO REACH AROUND 90F IN SPOTS...DEWPOINTS IN THE 60S SO IT WILL ALSO BE MUGGY. MODELS INDICATE THAT THE FRONT AND POTENTIAL OPEN WAVE REACH OUR AREA DURING THE WED NIGHT/THU TIMEFRAME. UPPER TROUGH WILL BE CROSSING OUR AREA DURING THIS TIMEFRAME AS WELL...RESULTING IN A BETTER CHANCE FOR SHOWERS/TSTMS WED NIGHT INTO PROBABLY THU NIGHT. PRECIPITABLE WATER INCREASES TO AROUND 2 INCHES...LENDING THE POTENTIAL FOR LOCALLY HEAVY DOWNPOURS ON THU. FRI... LATEST OPERATIONAL MODELS INCLUDING 00Z AND 12Z ECMWF ARE A BIT QUICKER WITH THE SURFACE FRONT AND ASSOCIATED LOW PRESSURE CENTER...INDICATING THEY MAY BE OFFSHORE FOR 12Z FRI WITH HIGH PRESSURE BUILDING IN FROM THE W IN ITS WAKE. HOWEVER THE UPPER TROUGH MAY LINGER...WHICH COULD CONTRIBUTE TO A POSSIBILITY OF SPOT DIURNAL SHOWERS. WILL CONTINUE SLIGHT CHANCE FOR SHOWERS ON FRI. NEXT WEEKEND... WITH LATEST MODEL SUITE INCLUDING 00Z/12Z ECMWF MUCH QUICKER WITH PREVIOUSLY MENTIONED COLD FRONT...A PERIOD OF HIGH PRESSURE AND UPPER LEVEL RIDGING MAY BRING DRY CONDITIONS FOR SATURDAY. HOWEVER...THE APPROACH OF ANOTHER FRONT MAY BRING UNSETTLED WEATHER FOR SUNDAY.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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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 SUNDAY NIGHT/...MODERATE CONFIDENCE. VFR. 5-10 KT EASTERLY FLOW FOR A MAJORITY OF THE FORECAST PERIOD. BKN-OVC 10 KFT CIGS OR HIGHER EXCEPT ACROSS THE IMMEDIATE S/SE COASTLINE WHERE A CHANCE SHRA IS POSSIBLE BEGINNING LATE TONIGHT AND CONTINUING THROUGH LATE SUNDAY ALONG WITH THE POSSIBILITY OF AT LEAST LOW-END VFR CIGS...POSSIBLY DOWN TO MVFR. POTENTIAL PATCHY FOG THIS EVENING. BLANKET OF CLOUDS IS CRITICAL WITH REGARDS TO LOWS TONIGHT. CROSSOVER THRESHOLDS WILL NEED TO BE MONITORED. IF IT COOLS CONSIDERABLY EVENING...PATCHY FOG IS POSSIBLE AT TERMINALS. WILL HOLD AT 6SM BR. NOT ENOUGH CONFIDENCE TO GO MVFR NOR IFR AT THIS TIME. DO NOT EXPECT ANY VSBY IMPACTS WITH SHRA. KBOS TAF...HIGH CONFIDENCE IN TAF. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...MONDAY THROUGH THURSDAY... MONDAY THROUGH WEDNESDAY...MODERATE CONFIDENCE. WHILE VFR WILL LIKELY DOMINATE MOST DAYS...SOME OVERNIGHT FOG/STRATUS MAY LEAD TO MVFR/IFR CONDITIONS MON NIGHT AND TUE NIGHT. MAIN AREA OF CONCERN IS SOUTH COASTAL LOCATIONS. CHANCE FOR LOCALIZED MVFR/IFR CONDITIONS IN SHOWERS AND THUNDERSTORMS WED AND THU.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. THROUGH SUNDAY...HIGH CONFIDENCE. AS THE PREVIOUS FORECASTER NOTED...WAVE MODELS CONTINUE TO OVER- FORECAST WAVE HEIGHTS OFF OUR COAST BY ABOUT A FOOT. LOWERED THE WAVE HEIGHT GUIDANCE BY 25 PERCENT THROUGH THE FORECAST PERIOD. TRANQUIL BOATING WEATHER CONTINUES WITH EASTERLY WINDS AROUND 5-10 KTS. WINDS AND SEAS BELOW SMALL-CRAFT ADVISORY LEVELS. WILL SEE A CHANCE OF SHOWERS ACROSS THE S/SE WATERS AND ADJACENT SHOWERS BEGINNING LATE TONIGHT INTO LATE SUNDAY. OUTLOOK...MONDAY THROUGH THURSDAY... THE AREA OF LOW PRESSURE WILL MOVE FURTHER OFFSHORE...WITH SURFACE HIGH PRESSURE BUILDING OVER THE WATERS. MODERATE CONFIDENCE THAT WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS DURING MONDAY THROUGH THROUGH THE DAY ON WEDNESDAY. BUT A FEW WIND GUSTS AND HIGHER SEAS ARE POSSIBLE ON WED AS THE SW WINDS INCREASE. PATCHY FOG MAY LEAD TO VSBY RESTRICTIONS DURING MON AND TUE NIGHTS. FOR WEDNESDAY NIGHT AND THURSDAY THE APPROACH OF A COLD FRONT AND ASSOCIATED LOW PRESSURE WILL BRING INCREASING SW FLOW...AND THE CHANCE FOR SCA WINDS/SEAS AS WELL AS SCATTERED SHOWERS/TSTMS.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...SIPPRELL/NMB NEAR TERM...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...NMB AVIATION...SIPPRELL/NMB MARINE...SIPPRELL/NMB

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