Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240827 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 427 AM EDT TUE MAR 24 2015 .SYNOPSIS... A DISTURBANCE PASSES SOUTH OF NEW ENGLAND THIS MORNING. HIGH PRESSURE BRINGS DRY AND COLD CONDITIONS TODAY...THEN MOVES OFFSHORE WEDNESDAY ALLOWING MORE SEASONABLE AIR TO RETURN. A WARM FRONT MOVES THROUGH THE REGION WEDNESDAY NIGHT. A COLD FRONT THEN SWEEPS ACROSS THE REGION THURSDAY NIGHT BRINGING HEAVY RAIN TO THE REGION. A SECOND COLD FRONT MOVES THROUGH ON FRIDAY BRINGING IN BLUSTERY AND WELL BELOW AVERAGE TEMPERATURES LASTING INTO THE WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THROUGH 8 AM/12Z... HIGH PRESSURE CENTERED OVER ONTARIO COVERS THE NORTHEAST USA AND TRENDS SOUTHEAST. INVERTED SURFACE TROUGH MOVING ACROSS THE CENTRAL APPALACHIANS TRENDING EAST. THE TROUGH IS CAUSING SNOW OVER SOUTHWEST PA AND NORTHERN WEST VIRGINA...BUT JUST MID CLOUDS FARTHER NORTH. THE MOVEMENT OF THE HIGH SHOULD BLOCK THE PRECIP FROM MOVING INTO OUR AREA...BUT WILL ALLOW MID AND HIGH CLOUDS OVER THE REGION DURING THE NIGHT. THERE HAS BEEN A CONCERN ABOUT OCEAN EFFECT CLOUDS REACHING INTO CAPE COD FROM THE GULF OF MAINE. THE EXISTING CLOUD SHIELD IS WELL EAST OF CAPE COD AND MOVING EAST. A NARROW AREA OF CLOUDS DOES EXTEND WEST FROM THE CLOUD SHIELD BUT TERMINATES EAST OF THE OUTER CAPE. SURFACE WINDS 010 DEGREES AT PROVINCETOWN WITH 10-15 KNOT SPEEDS ACROSS STELLWAGEN BANK...BUT LESS THAN 10 KNOTS FARTHER WEST. WATER TEMPS GENERALLY 2-4C WHILE 00Z CHH SOUNDING SHOWS -10C ALOFT. THUS THE WINDS AND TEMPS ARE MARGINAL FOR OCEAN EFFECT CLOUDS...MAINLY RIGHT ALONG THE OUTER CAPE AND MOSTLY TO THE EAST. IT IS POSSIBLE THE OUTER CAPE GETS CLIPPED BUT CONFIDENCE IS LOW. RADIATIONAL COOLING INLAND WITH DEWPOINTS IN THE SINGLE NUMBERS. WILL MAINTAIN MIN TEMPS IN THE TEENS WITH SINGLE NUMBERS IN NORTHWEST MASS. TODAY... HIGH PRESSURE WILL KEEP THE WEATHER DRY WITH A DIMINISHING NORTH WIND BECOMING LIGHT/VARIABLE. LINGERING MID CLOUDS IN THE MORNING MOSTLY SOUTH OF THE MASS PIKE BUT MOVING OFFSHORE BY AFTERNOON. MIXING REACHES TO AROUND 925 MB...WHERE TEMPERATURES SUPPORT AFTERNOON MAX SFC TEMPS IN THE 30S. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... TONIGHT... HIGH PRESSURE OVERHEAD WILL BRING CLEAR SKIES AND LIGHT WIND. THIS WILL SET UP FAVORABLE RADIATIONAL COOLING. WITH DEWPOINTS IN THE TEENS AND LOWER 20S...EXPECT MIN TEMPS TO BE CLOSE TO THESE LEVELS. WEDNESDAY... HIGH PRESSURE MOVES OFFSHORE AND SETS UP A SOUTH-SOUTHWEST FLOW OF AIR. EVEN WITH THE COLD START...TEMPS SHOULD BE ABLE TO REBOUND BY THE AFTERNOON. MIXING WILL BE MORE SHALLOW...BUT TEMPS ALOFT WILL SUPPORT MAX AFTERNOON TEMPS IN THE 40S. MOISTURE PROFILES SHOW INCREASING CLOUDS THROUGH THE DAY. DURING THE MORNING THIS IS MOSTLY CIRRUS-LEVEL MOISTURE...BUT BY MID-LATE AFTERNOON THE PROFILES SHOW CLOUDS GETTING LOWER AND THICKER. AT 18Z THE LOW LEVEL JET AND ASSOCIATED LIFT IS AIMED AT WESTERN/CENTRAL NEW YORK. SO WE EXPECT ANY PCPN AT THAT TIME TO BE WELL TO OUR WEST. BY EVENING THE JET SHIFTS EAST AND WOULD SUPPORT PCPN ENTERING SOUTHERN NEW ENGLAND. TEMPERATURE PROFILES ARE WARM ENOUGH FOR RAIN. SO MOST OF THE DAY SHOULD BE DRY...WITH A CHANCE OF RAIN LATE AFTERNOON/EVENING. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... HIGHLIGHTS... * WARM BUT HEAVY RAIN ON THURSDAY AHEAD OF COLD FRONT * BLUSTERY AND BELOW AVERAGE TEMPS FOR THE WEEKEND * WEAK DISTURBANCE POSSIBLE ON MONDAY MODEL GUIDANCE... LATEST GUIDANCE IS SUGGESTING THAT THE AMPLIFIED WRN RIDGE/ERN TROUGH PATTERN FCST TO BE IN PLACE FOR MOST OF THE PERIOD MAY BEGIN TO EVOLVE TOWARD FLATTER MEAN FLOW BY NEXT WEEK. WHILE SOME EMBEDDED DETAILS WITHIN THE RIDGE/TROUGH CONFIGURATION HAVE BEEN AND CONTINUE TO BE PROBLEMATIC... ENSEMBLE GUIDANCE AND THE LIKELY TREND TOWARD FLATTER FLOW SUGGEST THAT OVERALL PREDICTABILITY OF SIGNIFICANT FEATURES MAY DECLINE RAPIDLY AFTER EARLY NEXT WEEK. OVERALL AMPLIFIED PATTERN WILL CONTINUE WITH 00Z GUIDANCE IN GOOD AGREEMENT. STILL SOME TIMING/INTENSITY ISSUES FOR UPCOMING WED PM INTO FRIDAY SYSTEM. SEVERAL SHORTWAVES WILL MOVE THROUGH THE FLOW DEVELOPING WAVES ALONG STALLED FRONTAL SYSTEM. DEPENDING ON INTENSITY AND STRENGTH...COULD HAVE FLOODING ISSUES FROM LEFTOVER SNOWPACK AND HIGH DEWPOINTS. OTHERWISE GUIDANCE IS IN GOOD AGREEMENT WITH POLAR JET DROPPING SOUTH...BRINGING BELOW AVG TEMPS FOR THE WEEK. GUIDANCE IS THEN SPLIT ON WEAK WAVE PASSING ON MONDAY. DETAILS... * WEDNESDAY NIGHT INTO FRIDAY...MODERATE CONFIDENCE. HIGH CONFIDENCE PRECIP WILL OCCUR LOWER CONFIDENCE ON EXACT TIMING. JUST ONE OF MANY SHORTWAVES WILL PASS THROUGH THE FLOW ON WEDNESDAY NIGHT. AS WARM FRONT APPROACHES...TEMPS AND DEWPOINTS WILL REMAINS STEADY/SLOWLY INCREASE THROUGH THE NIGHT. THIS WILL INCREASE THE FOG POTENTIAL AND WE COULD SEE WIDESPREAD DENSE FOG. LOW CONFIDENCE ON WHERE EXACTLY THIS FAR OUT. PRECIP WILL BEGIN TO INCREASE IN THE MORNING HOURS AS THE FIRST WAVE WILL MOVE OFFSHORE BY EARLY WED NIGHT. THIS PRECIP WILL BE ALONG THE EAST TO WEST WARM FRONT AS IT MOVES INTO SOUTHERN NEW ENGLAND. BIGGEST QUESTION IS HOW FAR NORTH WILL THE FRONT REACH. GUIDANCE SEEMS TO ALWAYS STRUGGLE WITH THAT ASPECT...THEREFORE TRENDED A MODEL BLEND TO GET A DOWN THE MIDDLE APPROACH. TEMPS SOUTH OF THE FRONT WILL REACH INTO THE MID TO PERHAPS THE UPPER 50S WHILE NORTHWARDS WILL STAY IN THE 40S. REGARDLESS RAIN WILL BE OVERSPREADING FROM SOUTH TO NORTH ON THURSDAY WITHIN A VERY MOIST ENVIRONMENT AS DEWPOINTS CONTINUE TO RISE. THURSDAY AFTERNOON INTO THE OVERNIGHT HOURS SEEMS TO BE WHEN THE HEAVIEST PRECIP WILL OCCUR. NEXT SHORTWAVE WILL PUSH THROUGH ALLOWING FOR SURFACE LOW DEVELOPMENT ALONG THE EXTENDED COLD FRONT APPROACHING SOUTHERN NEW ENGLAND. THIS FRONT WILL BE THE FOCUS ON THE HEAVY PRECIP DURING THE AFTERNOON/EVENING HOURS. SW LLJ WILL BE ON THE INCREASE REACHING 50-65 KTS ACROSS THE REGION POOLING IN MORE MOISTURE INTO THE AREA. PWAT VALUES ARE ABOVE 1 INCH WHICH IS 2 TO 3 STANDARD DEVIATIONS AWAY WHILE THE MOISTURE FLUX IS 4 TO 5 STANDARD DEVIATIONS AWAY. DUE TO THE AMOUNT OF MOISTURE IN THE ATMOSPHERE AND THE APPROACHING FRONTAL SYSTEM...EXPECT HEAVY DOWNPOURS AND PERHAPS ISOLATED THUNDER. IN FACT MODELS HAVE INCREASED THEIR QPF FROM JUST 12 HOURS AGO. WITHIN THESE HEAVY DOWNPOURS...WE COULD MIX DOWN THE GUSTY WINDS ALOFT DOWN TO THE SURFACE. THIS HIGHLY ANOMALOUS SYSTEM COMBINED WITH THE SNOW PACK...COULD SEE SIGNIFICANT INCREASE IN RUNOFF AND RISES IN AREA STREAMS FROM WHAT WILL LIKELY BE MAJOR SNOWMELT. MORE DETAILS IN HYDRO SECTION. AS FRONT PASSES THROUGH PRECIP WILL END FROM WEST TO EAST OVERNIGHT THURSDAY INTO FRIDAY MORNING. FRIDAY WE WILL BEGIN TO DRY OUT AS TEMPS WARM INTO THE MID TO LOWER 40S. A SECONDARY COLD FRONT WILL PASS THROUGH LATE FRIDAY BRINGING IN STRONG CAA AND BLUSTERY CONDITIONS. * THE WEEKEND...HIGH CONFIDENCE IN TEMPS. DEEP UPPER LEVEL TROUGH WILL MOVE FROM THE GREAT LAKES TO OVER SOUTHERN NEW ENGLAND. THIS TROUGH AXIS WILL SETTLE OVER THE REGION LATE FRIDAY INTO SATURDAY. WELL BELOW AVG TEMPS ARE EXPECTED AT 850MB TEMPS DROP DOWN TO -12C. HOWEVER...WEAK RIDGE WILL PASS THROUGH ON SUNDAY INCREASE TEMPS AND ALLOWING FOR A MOSTLY PLEASANT DAY WITH HIGH TEMPS REACHING THE MID TO UPPER 40S. MONDAY...LOW CONFIDENCE. NEXT UPPER LEVEL DISTURBANCE WILL IMPACT SOUTHERN NEW ENGLAND LATE SUNDAY INTO MONDAY. THIS SYSTEM WILL BRING PRECIP AND COOLER TEMPS TO THE REGION. THIS MAY CAUSE FOR P-TYPE ISSUES BUT IT WILL NEED TO BE WATCHED OVER THE NEXT SEVERAL DAYS. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. HIGH CONFIDENCE THROUGH WEDNESDAY. VFR THROUGH THE PERIOD. CLOUDS LOWER AND THICKEN WEDNESDAY AFTERNOON AND EVENING WITH MVFR CIGS/VSBYS POSSIBLE WEDNESDAY EVENING ESPECIALLY IN THE CT VALLEY. KBOS TAF...HIGH CONFIDENCE. KBDL TAF...HIGH CONFIDENCE. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY...MODERATE TO HIGH CONFIDENCE WEDNESDAY NIGHT THROUGH THURSDAY MORNING...GENERALLY VFR CONDITIONS EXCEPT POSSIBLY MVFR CIGS ALONG SOUTH COAST WEDNESDAY NIGHT INTO THE THURSDAY MORNING. IFR IS POSSIBLE IN FOG OVERSPREADING THE REGION. THURSDAY AFTERNOON AND NIGHT...WIDESPREAD MVFR CIGS AND VSBYS IN SHOWERS. MAY SEE AREAS OF IFR CIGS/VSBY IN HEAVY DOWNPOURS. LOW RISK OF THUNDER. FRIDAY THROUGH SATURDAY...VFR CONDITIONS LIKELY. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. HIGH CONFIDENCE THROUGH WEDNESDAY. HIGH PRESSURE BUILDS OVER THE WATERS TODAY AND MOVES OFFSHORE WEDNESDAY. DIMINISHING NORTH WIND TODAY BECOMES VARIABLE TONIGHT AND SOUTH-SOUTHWEST WEDNESDAY. WINDS REMAIN BELOW 20 KNOTS AND SEAS BELOW 5 FEET THROUGH THE PERIOD. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY... MODERATE TO HIGH CONFIDENCE THROUGH FRIDAY. MODERATE CONFIDENCE FRIDAY NIGHT INTO SATURDAY. CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CONDITIONS WEDNESDAY NIGHT THROUGH THURSDAY MORNING. STRONG SW WINDS DEVELOP ALOFT THURSDAY AFTERNOON AND EVENING BUT ANTICIPATE ONLY SOME OF THE WINDS MIXING TO THE SURFACE. MAY NEED A GALE WATCH BUT DEF SMALL CRAFT ADVISORY. AREAS OF DENSE FOG MAY BE A SIGNIFICANT HAZARD WED NIGHT INTO THURSDAY...ESPECIALLY ALONG THE SOUTH COASTAL WATERS. THERE IS A LOW RISK THAT JUST ENOUGH COLD AIR ADVECTION WITH NORTHERLY WINDS FRIDAY NIGHT AND SATURDAY COULD CAUSE A PERIOD NEARING SMALL CRAFT ADVISORY WIND GUSTS...BUT CURRENTLY LOOKS MORE LIKELY THAT GUSTS WILL NOT EXCEED 20 KT. && .HYDROLOGY... SEVERAL FACTORS ARE OCCURRING ON THURSDAY WHICH WILL INCREASE THE POTENTIAL FOR RUNOFF AND RISES IN AREA STREAMS. FIRST IS THE ANOMALOUS DEWPOINTS WHICH WILL BE STREAMING INTO THE REGION. 40+F DEWPOINTS WILL HELP EAT AWAY AT THE SNOW PACK ON TOP OF 50+ DEGREE TEMPERATURES. THIS MOISTURE LADEN AIR WILL ALLOW FOR CONDENSATION AND THUS HEAT UPON THE SNOW PACK INCREASING THE RATE OF MELTING. GUIDANCE SNOWS THAT THERE IS STILL ABOUT 2-5 INCHES OF WATER WITHIN THE SNOW PACK OR SWE...ACROSS THE REGION SO THESE HIGH DEWPOINTS WILL HELP RELEASE A GOOD PORTION OF THIS WATER. SECOND ASPECT IS THE UPCOMING RAIN POTENTIAL. EXPECT AROUND AN INCH OF QPF TO OCCUR ACROSS SOUTHERN NEW ENGLAND WITH HIGHER AMOUNTS LIKELY WITHIN HEAVIER DOWNPOURS BY THURSDAY NIGHT INTO FRIDAY MORNING. THEREFORE COMBINING THE RAPID SNOW MELT WITH THE UPCOMING QPF...WE COULD SEE ON THE ORDER OF 1.5-3 INCHES OF WATER HEADING INTO AREA RIVERS AND STREAMS. CURRENTLY THINK THAT SOME RIVERS WILL GET CLOSE TO OR ABOVE MINOR FLOODING...BUT MOST WILL FALL SHORT OF FLOOD LEVELS. HOWEVER IF DEWPOINTS ARE HIGHER OR QPF INCREASES THEN SEVERAL STREAMS WILL GO INTO FLOOD. LASTLY...MINOR URBAN FLOODING ALSO LOOKS LIKE A POSSIBILITY ESP IF DRAINAGE SYSTEMS ARE STILL BLOCKED FROM SNOW. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/DUNTEN NEAR TERM...WTB SHORT TERM...WTB LONG TERM...DUNTEN AVIATION...WTB/DUNTEN MARINE...WTB/DUNTEN HYDROLOGY...DUNTEN

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