Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 212302 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 702 PM EDT MON JUL 21 2014 .SYNOPSIS... SOUTHERLY FLOW WILL RETURN OVERNIGHT ALLOWING FOR AN INCREASE IN HEAT AND HUMIDITY. SHOWERS AND THUNDERSTORMS WILL DEVELOP ON WEDNESDAY AND LAST INTO THURSDAY AS A COLD FRONT SWEEPS THE REGION. LESS HUMID AND DRIER AIR WILL MOVE IN BY FRIDAY LASTING THROUGH THE WEEKEND. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 7 PM UPDATE... LOW CLOUDS AND FOG CONTINUE TO SWIRL ABOUT THE WATERS ADJACENT TO CAPE COD. DIFFICULT TO FORECAST...BUT BASED ON THE VISIBILITY AND CLOUD TRENDS PER THE HRRR...AND H975-950 WIND AND RH FIELDS PER THE RAP...PRESENT NE-FLOW WILL GRADUALLY VEER E/SE BEFORE SHIFTING OUT OF THE W/SW AFTER MIDNIGHT. NOTING LOW-60 DEWPOINTS LIKELY TO INCREASE WITH THE SHIFTING WINDS...AS WELL AS THE LATEST MOS GUIDANCE...EXPECT THE OFFSHORE LOW CLOUDS PER SATELLITE TO PIVOT AND ADVECT BACK ONSHORE ALONG THE S/SE COASTLINE. HAVE AMENDED SKY AND VISIBILITY GRIDS ACCORDINGLY WITH THE MENTION OF DENSE FOG. HAVE TO MONITOR CLOSELY AS TO WHETHER HEADLINES ARE NECESSARY. AT PRESENT...HIGHEST CONFIDENCE OF NANTUCKET BECOMING SOCKED IN OVERNIGHT. OTHERWISE THE REMAINDER OF THE FORECAST REMAINS ON TRACK. HIGH PRESSURE BUILDS E OF THE REGION ALLOWING FOR RETURN S-FLOW AND INCREASING MOISTURE. MAY HAVE TO MONITOR FOR DENSE FOG DEVELOPMENT ACROSS INTERIOR SHELTERED LOCALES ACROSS INTERIOR NEW ENGLAND. MAY BE HAMPERED BY MID-LEVEL CLOUD DEBRIS DISCERNIBLE VIA IR SATELLITE OVER UPSTATE-NY. NEVERTHELESS...HAVE A MENTION OF FOG FOR THE MID- TO UPPER-CT VALLEY REGION. LOWS DOWN TO THE LOW-60S...LIKELY LOWER FOR THOSE AREAS WHICH REMAIN CLEAR AND CAN EFFECTIVELY RADIATE OUT. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... TOMORROW... UPPER LEVEL RIDGING WILL CONTINUE TO BUILD OVER THE REGION ON TUESDAY AND THUS A WARMER AND MORE HUMID DAY IS EXPECTED FOR THE ENTIRE AREA. TEMPS WILL WARM WELL INTO THE MID TO UPPER 80S AND WITH SOUTHWESTERLY FLOW...DEWPOINTS WILL CONTINUE TO RISE INCREASING THE HUMIDITY. ASIDE FROM THE RETURN OF NEW ENGLAND SUMMER...GUIDANCE CONTINUES TO SHOW QPF TOMORROW IN SHOWERS AND THUNDERSTORMS. BELIEVE THIS THREAT IS BEING OVERPLAYED BY THE MODELS AS WITH THE RISING HEIGHTS AND INCREASING TEMPS ALOFT...WILL CREATE A CAP LIMITING THUNDERSTORM POTENTIAL. BELIEVE DIURNAL CU WILL DEVELOP ACROSS A GOOD PORTION OF THE INTERIOR. AT THE VERY LEAST A POP-UP SHOWER/THUNDERSTORM MAY GIVE WAY AFTER SUNSET WHEN THE CAP WEAKENS SLIGHTLY BUT STILL HAVE A LOW CONFIDENCE. THEREFORE KEPT POPS BELOW 20S AND INCLUDED ISOLATED WORDING. TOMORROW NIGHT... ANY LINGERING CONVECTION SHOULD CEASE JUST AFTER SUNSET DUE TO THE LOSS OF DAYTIME HEATING. A STRENGTHEN SOUTHWESTERLY FLOW WILL CONTINUE TO INCREASE THE LOW LEVEL MOISTURE WITH DEWPOINT CLIMBING WELL INTO THE MID TO UPPER 60S. COULD SEE ANOTHER ROUND OF FOG DEVELOPING OVERNIGHT...ESPECIALLY IN THE NORMALLY PRONE REGIONS AND VALLEY LOCATIONS. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... */ HIGHLIGHTS... - HOT AND HUMID WEDNESDAY...THUNDERSTORMS TO THE WEST - POSSIBLE HEAVY RAIN AND FLASH FLOOD THREAT WEDNESDAY NIGHT - THREATS CONTINUING INTO THURSDAY FOR S/E NEW ENGLAND - DRY AND COOLER WEATHER FRIDAY - UNCERTAIN FORECAST FOR THE WEEKEND */ OVERVIEW AND MODEL PREFERENCE... SOME DIFFICULTY IN DISCERNING THE N HEMISPHERIC PATTERN. NAO/AO PATTERNS ARE NEAR-NEUTRAL WHILE THE MJO IS CONCLUDED AS INCOHERENT BY CPC. LIKELY COMPLICATIONS WITH W PACIFIC TROPICAL DISTURBANCES BECOMING USURPED WITHIN THE UPPER-LEVEL FLOW AS EVIDENCED BY THE LARGE VARIABILITY IN ENSEMBLE PNA FORECASTS. BUT NOTABLY THUS FAR WITHIN THE FIRST-HALF OF JULY...POSITIVE H5 HEIGHT ANOMALIES ARE APPARENT OVER THE NE PACIFIC AND NW ATLANTIC. THIS IS RESULTING IN THE OVERALL FLOW PATTERN TO BUCKLE WITH PREFERRED TROUGHING ACROSS THE GREAT LAKES AND E-HALF OF THE CONUS COLLOCATED WITH AN ANOMALOUS INCREASE AND CYCLONIC-NATURE OF THE H2 JET. SO WHILE NO CERTAINTY AS HOW THE LONG-TERM PATTERN MAY EVOLVE... WILL PREVAIL WITH PRESENT BUCKLING PATTERN AND PREFERRED TROUGHING ACROSS THE E-HALF OF THE CONUS. COINCIDING WITH THE 6-10/8-14 DAY TEMPERATURE OUTLOOKS PER CPC...BELOW-NORMAL TEMPERATURES ARE LIKELY. BUT EVALUATING THE NAEFS AND EC ENSEMBLE...ITS ANTICIPATED THAT THE NE CONUS WILL RESIDE WITHIN THE E-PERIPHERY OF THE PREFERRED TROUGH PATTERN THUS IN PROXIMITY TO CYCLONICALLY DIGGING DISTURBANCES. WITH ANY WOBBLE IN THE PATTERN...WE COULD FIND OURSELVES ON EITHER THE WARM OR COOL SIDE OF THE PATTERN. THIS LENDS TO OBVIOUSLY DECREASING CONFIDENCE FURTHER OUT IN THE FORECAST. BASED ON A CONSENSUS OF MODEL SOLUTIONS...WILL OUTLINE HIGH POINTS ALONG WITH CONFIDENCE AND PREFERRED GUIDANCE IN THE DAILIES BELOW. */ DAY-TO-DAY DETAILS... WEDNESDAY... SW-NE ORIENTED COLD FRONT SWEEPS GRADUALLY SE INTO S NEW ENGLAND. WHILE THE EXACT TIMING OF THE FRONT REMAINS UNCERTAIN...OVERALL THERE IS CONSENSUS PATTERN OF LOW-LEVEL FORCING OF SW TROPICAL FLOW ALONG AND AHEAD OF THE FRONT THAT UNDERGOES DEEP-LAYER LIFT PER MID- LEVEL IMPULSE AND RRQ OF THE UPPER-LEVEL JET...THE BETTER OF WHICH APPEARS TO RESIDE ACROSS THE ST. LAWRENCE VALLEY INTO N NEW ENGLAND. SHOWERS AND THUNDERSTORMS ALONG AND AHEAD OF THE FRONT ARE LIKELY. UPON A CONSENSUS...EXPECT THE FRONT INTO W NEW ENGLAND BY EVENING SWEEPING THROUGH THE REGION OVERNIGHT AND JUST OFFSHORE BY THURSDAY MORNING. WARM-SECTOR LOOKS TO BE CAPPED WITH TEMPERATURES AROUND H7 WARMING TO NEAR +10C. ANTICIPATE MUCH OF THE ACTIVITY IMMEDIATELY ALONG THE FRONT WHERE THE GREATEST FORCING RESIDES ALLOWING THE ATMOSPHERE TO SATURATE AND THE CAP TO BREAK. WITH THE MAINLY NOCTURNAL PASSAGE...INSTABILITY BECOMES ELEVATED IN A REGION OF STRONG SW-NE UNIDIRECTIONAL SHEAR. CONVECTIVE THREATS SUCH AS DAMAGING WIND ARE POSSIBLE...BUT WITH A STABILIZING BOUNDARY LAYER...THAT BECOMES MORE DIFFICULT. MAIN CONCERN IS WITH PWATS EDGING UP TO 2-INCHES AND THE POTENTIAL THREAT OF FLASH FLOODING. THE LIKELIHOOD FOR AREAS OF DEEP-LAYER ASCENT ALONG WITH OROGRAPHICAL INFLUENCES...THERE ARE LIKELY TO BE AREAS OF HEAVY RAIN. WILL EMPHASIZE HEAVY RAINS AND GUSTY WINDS INITIALLY FOR W NEW ENGLAND...WITH HEAVY RAIN FOR THE EVENING FOR THE OVERNIGHT PERIOD. SOME FINAL NOTES...EXPECT LOW STRATUS IMPACTING S/SE COASTAL NEW ENGLAND AS HIGH THETA-E/DEWPOINT MOISTURE UNDERGOES WEAK ISENTROPIC ASCENT. SOME DRIZZLE/LIGHT SHOWERS POSSIBLE AS WELL PRIOR TO THE APPROACH OF THE COLD FRONT OVERNIGHT. OTHERWISE...HOT HUMID AND STICKY DURING THE DAY. HIGHS NEAR 90-DEGREES CERTAINLY PLAUSIBLE FOR THOSE AREAS THAT REMAIN UNDER SUNSHINE. THURSDAY... ALL GUIDANCE AGREES UPON THE COLD FRONT PUSHING OFFSHORE BY LATE IN THE DAY INTO EVENING...THOUGH THE DEVELOPMENT OF A SECONDARY LOW ALONG THE COLD FRONT COULD DRAG ENERGY BACK N/W TOWARDS LOWER HEIGHTS ASSOCIATED WITH THE H5 TROUGH. THUS WILL HOLD WITH SHOWERS AND POSSIBLE THUNDERSTORMS FOR S/E NEW ENGLAND. CONTINUED CONCERN OF DEEP-LAYER LIFT EXACERBATING POCKETS OF HEAVY RAIN LEADING TO FLASH FLOODING. SUCH THREATS WILL NEED TO BE MONITORED MAINLY FOR THE EARLY-HALF OF THE DAY WHERE PWATS UP TO 2-INCHES PREVAIL. FRIDAY... TROUGH AXIS SWEEPS ACROSS THE REGION ATTENDANT WITH HIGH PRESSURE AND H85 TEMPERATURES FALLING TO AROUND +12C. WILL PREVAIL WITH QUIET WEATHER ALONG WITH SEASONABLE AND DRY CONDITIONS. PERHAPS SOME WEAK SEA-BREEZES ALONG THE IMMEDIATE COASTLINES. WEEKEND INTO EARLY NEXT WEEK... THROWING OUT THE DETERMINISTIC GUIDANCE AND KEEP WITH THE NAEFS... GFS AND EC ENSEMBLE GUIDANCE. PROLONGED TROUGHING IS PREFERRED ALONG WITH BELOW-NORMAL CONDITIONS. AS TO WHETHER SIGNIFICANT WEATHER DISTURBANCES WILL FLUTTER ACROSS THE REGION DURING THIS TIMEFRAME REMAINS UNCERTAIN. NEVERTHELESS...A SEASONABLE AND ACTIVE PATTERN IS ANTICIPATED...THE SPECIFICS AND TIMING OF WHICH ARE UNKNOWN. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY NIGHT/...MODERATE CONFIDENCE. OFFSHORE IFR CIGS/VSBYS TO REMAIN A NUISANCE OVERNIGHT FOR THE S/SE COASTLINE TERMINALS AS WINDS VEER E/SE BEFORE BECOMING SW. HAVE HIGHEST CONFIDENCE ACROSS ACK...LESSER IMPACTS ELSEWHERE... THOUGH CAN NOT RULE OUT THOSE LOCATIONS SEEING SIMILAR SOCKED IN CONDITIONS. PERIODS OF MVFR-IFR POSSIBLE OVER N/W INTERIOR NEW ENGLAND. TERMINALS IMPROVE VFR INTO TUESDAY AS LOW CIGS AND FOG SLINK OFF TO THE SE. SPOT SHOWERS POSSIBLE ACROSS THE INTERIOR...OTHERWISE DIURNAL CU AROUND 5 KFT. WHILE MAINLY VFR OVERNIGHT...THE THREAT OF MVFR/IFR FOG IS POSSIBLE WITH THE BEST CHANCE ALONG THE S/SE COASTLINE TERMINALS. KBOS TAF...MODERATE CONFIDENCE IN TAF. WILL REMOVE THE MENTION OF FOG BASED ON MESOSCALE MODEL TRENDS...BUT SOME CONCERN AS TO WHETHER TRENDS THE PREVIOUS EVENING WILL OCCUR AGAIN TONIGHT. WILL CLOSELY MONITOR. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...WEDNESDAY THROUGH SATURDAY... WEDNESDAY INTO THURSDAY...MODERATE CONFIDENCE. MAINLY VFR. SWEEPING COLD FRONT AHEAD OF WHICH TSRA/+RA AND SW WINDS GUSTING 25 KTS POSSIBLE. TEMPO MVFR-IFR. LOW MVFR-IFR CIGS AND FOG POSSIBLE FOR IMMEDIATE S/SE COASTLINE TERMINALS. TIMING FROM LATE WEDNESDAY INTO MIDDAY THURSDAY. IMPROVEMENT NW-SE THURSDAY. WINDS BACK NW BEHIND THE FRONT AND ARE WEAKER. FRIDAY INTO SATURDAY...MODERATE CONFIDENCE. VFR. LIGHT N WINDS BACKING W/SW WITH TIME. SEA-BREEZES ALONG IMMEDIATE SHORES DURING THE DAY POSSIBLE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY NIGHT/...MODERATE CONFIDENCE. A PERIOD OF MAINLY QUIET BOATING WEATHER IS EXPECTED AS HIGH PRES BUILDS ACROSS THE WATERS. THERE IS A POSSIBILITY THAT SCA MAY BE NEEDED FOR THE NEAR SHORE AS WINDS MAY REACH 25KTS DURING THE LATE AFTERNOON HOURS TOMORROW. OTHERWISE...WILL HAVE TO MONITOR FOR SOME FOG AND LOW VISIBILITY ACROSS THE WATERS TONIGHT AND AGAIN TUESDAY NIGHT. BUT ONLY HAVE LOW CONFIDENCE IN WHERE OR IF...IT WILL FORM. OUTLOOK...WEDNESDAY THROUGH SATURDAY... WEDNESDAY INTO THURSDAY...MODERATE CONFIDENCE. COLD FRONT SWEEPING ACROSS THE WATERS BEGINNING AFTER MIDNIGHT THURSDAY AND CONTINUING THROUGH THE DAY. LOW CLOUDS AND FOG POSSIBLE AHEAD INITIALLY ALONG THE S/SE WATERS...FOLLOWED BY LATER THREATS OF THUNDERSTORMS AND HEAVY RAIN. VISIBILITY IMPACTS POSSIBLE. GUSTY SW WINDS UP TO 25 KTS WILL PUSH SEAS IN EXCESS OF 5 FEET. SMALL-CRAFT ADVISORY CONDITIONS ANTICIPATED. WAVES BEGINNING TO DIMINISH BY LATE THURSDAY AS THE COLD FRONT PUSHES OUT TO SEA. FRIDAY INTO SATURDAY...MODERATE CONFIDENCE. HIGH PRESSURE BUILDING INTO THE WATERS ALLOWING WINDS TO RELAX OUT OF THE N AND LATER BACK SW. ANTICIPATE SEAS TO DIMINISH AND GOOD BOATING WEATHER TO PREVAIL NEAR THE BEGINNING OF THE FORECAST PERIOD. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...DUNTEN/SIPPRELL NEAR TERM...DUNTEN/SIPPRELL SHORT TERM...DUNTEN LONG TERM...SIPPRELL AVIATION...DUNTEN/SIPPRELL MARINE...DUNTEN/SIPPRELL

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