Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 281856 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 156 PM EST SUN DEC 28 2014 .SYNOPSIS... A COLD FRONT CROSSING NEW ENGLAND WILL MOVE OFFSHORE BY EVENING. HIGH PRESSURE BUILDS SOUTH FROM CANADA AND THEN SPREADS ACROSS THE USA FOR MUCH OF THE WEEK. THIS WILL MEAN A DRY AND COLD SPELL FOR NEW ENGLAND. A STORM MOVING OUT OF THE SOUTHERN PLAINS WILL MOVE TO THE GREAT LAKES SATURDAY AND BRING RAIN TO SOUTHERN NEW ENGLAND OVER NEXT WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... THROUGH 7 PM... COLD FRONT CROSSING NEW ENGLAND DURING THE AFTERNOON. THERE ARE LOTS OF CLOUDS WITH THIS FRONT BUT MOST OF THE ASSOCIATED SHOWERS HAVE MOVED OFFSHORE. PAST MOVEMENT OF THE FRONT EXTRAPOLATES IT OFF THE COAST BY 00Z. SATELLITE IMAGERY SHOWS LOTS OF CLOUDS EXTENDING BEHIND THE FRONT...SO SKIES SHOULD REMAIN MOSTLY CLOUDY THROUGH THE REMAINDER OF THE AFTERNOON/EVENING. TONIGHT... MUCH OF THE AIRMASS DRIES EARLY TONIGHT WHICH WOULD SUPPORT CLEARING SKIES. CROSS SECTIONS SHOW LINGERING MOISTURE /OVER 70 PCT RH/ NORTH OF THE MASS PIKE BELOW 900 MB THROUGH 12Z MONDAY. AREAS SOUTH OF THE PIKE ARE LESS MOIST BUT NOT BONE DRY. SO WILL KEEP CLOUDS AROUND EARLY NIGHT WITH A CLEARING TREND OVERNIGHT. TEMPERATURES IN THE 20S INLAND AND 30S ALONG THE COAST. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... FLAT FLOW ALOFT WITH SURFACE HIGH PRESSURE BUILDING THROUGH THE GREAT LAKES INTO CANADA. THIS SHOULD BE A DRY PERIOD WITH MOSTLY CLEAR SKIES. MIXING DURING THE DAY IS FORECAST TO REACH 900 MB. WINDS IN THIS LAYER WILL BE 15-20 KNOTS...SO WE WOULD EXPECT GUSTS UP TO 20 KNOTS DURING THE DAY. TEMPS AT 900 MB OF -3C TO -5C WOULD SUPPORT MAX SFC TEMPS OF 40-45. BUT WITH ZONAL FLOW ALOFT AND COLD ADVECTION IN PLAY WE WILL EDGE CLOSE TO SEASONAL NORMALS WITH FORECAST TEMPS IN THE MID 30S TO LOWER 40S. MONDAY NIGHT SHOULD ALSO BE DRY WITH SEASONAL MINS IN THE UPPER TEENS AND 20S. && .LONG TERM /TUESDAY THROUGH SUNDAY/... HIGHLIGHTS... * DRY AND COLD THROUGH FRIDAY * CHANCE OF RAIN OR MIXED PRECIPITATON TO RAIN ON SATURDAY AS WARM FRONT APPROACHES OVERVIEW... MEDIUM RANGE MODELS NOW APPEAR IN GOOD AGREEMENT ON AT LEAST THE LARGE SCALE PATTERN THROUGH NEXT WEEKEND. OVER THE COURSE OF THE COMING WEEK...A HIGH AMPLITUDE RIDGE BUILDS OVER ALASKA WHILE THE NORTH AMERICAN POLAR VORTEX SETS UP OVER HUDSON BAY. THIS OPENS THE DOOR TO ARCTIC INTRUSION INTO NEW ENGLAND BUT WITH WHAT WILL PROBABLY BE A TEMPORARY RELAPSE TO MILD TEMPERATURES NEXT WEEKEND IN ASSOCIATION WITH WHAT LOOKS TO BE STILL ANOTHER INSIDE RUNNER. ENSEMBLE MEMBERS SUGGEST A RETURN TO A POSITIVE NAO INDEX AFTER JAN 1 AND A STRONG RIDGE REMAINS ROOTED ACROSS THE BAHAMAS. THUS...ALTHOUGH THE PATTERN IN GENERAL FAVORS COLD TEMPERATURES ACROSS SOUTHERN NEW ENGLAND FOR THE FORESEEABLE FUTURE...SHORT WAVE ENERGY CAN DISLODGE THE COLD AIR AT LEAST TEMPORARILY WITH NO DOWNSTREAM BLOCKING AVAILABLE TO EITHER HOLD IN THE COLD AIR OR PROMOTE SIGNIFICANT COASTAL CYCLOGENESIS. DAY TO DAY... TUESDAY THROUGH WED...GENERALLY DRY AND COLDER THAN NORMAL TEMPERATURES SUPPORTED BY BROAD TROF ALOFT CENTERED OVER HUDSON BAY AND MASSIVE 1059 MB HIGH SPREADING S AND SE FROM WESTERN SASKATCHEWAN. TUE NIGHT/WED AM LOOKS TO BE THE COLDEST NIGHT WITH 850 MB TEMPERATURES OF -15C TO -16C...PROBABLY MOSTLY CLEAR SKIES AND LIGHT WINDS. WILL LIKELY EXPERIENCE SURFACE TEMPERATURES IN TEENS ACROSS MOST OF INTERIOR SOUTHERN NEW ENGLAND WITH POSSIBLY POCKETS OF 5 TO 10 ABOVE TEMPERATURES NW MA. LACK OF SNOWCOVER PREVENTS WHAT MIGHT OTHERWISE BE COLDER TEMPERATURES. WED NIGHT THROUGH FRI...SHORT WAVE TROF EMBEDDED IN BROAD CYCLONIC FLOW ALOFT PASSES ACROSS NEW ENGLAND ON THU BUT LACKS MOISTURE. HOWEVER...IT IS NOT OUT OF THE QUESTION THAT LOW LEVEL LAPSE RATES COULD SUPPORT OCEAN EFFECT FLURRIES OR SNOW SHOWERS ACROSS NANTUCKET WITH WESTERLY GRADIENT. THE 00Z GFS THERMAL PROFILE IS MORE FAVORABLE THAN THE 00Z ECMWF THERMAL PROFILE FOR THIS. THE OTHER POTENTIAL ISSUE FOR THU IS WIND. MEDIUM RANGE MODELS HAVE DEPICTED FOR QUITE A FEW RUNS A TIGHTENING OF THE SURFACE PRESSURE GRADIENT ON THU WITH BRISK WESTERLY WINDS THE RESULT...POSSIBLY GALE FORCE GUSTS JUST OFF THE COAST. THIS COULD MAKE THU FEEL COLDER DUE TO LOWER WIND CHILLS. WINDS WILL LIKELY SLACKEN BY FRI MORNING AS MEDIUM RANGE MODELS CONSISTENT WITH SURFACE RIDGE MOVING ACROSS THE REGION. FRI NIGHT THROUGH SAT...THIS IS THE ONLY VIABLE OPPORTUNITY FOR SIGNIFICANT PRECIPITATION DURING THIS FORECAST PERIOD. MEDIUM RANGE OPERATIONAL MODELS AND NEARLY ALL ENSEMBLE MEMBERS POINT TO AN INSIDE RUNNER WITH SOME VARIATIONS IN TIMING AND STRENGTH OF THE SYSTEM. AT THIS TIME IT LOOKS LIKE THIS SHOULD BE MAINLY A RAIN EVENT...BUT ENOUGH LOW LEVEL COLD AIR AT THE OUTSET COULD SET THE STAGE FOR A PERIOD OF MIXED PRECIPITATION AT THE START OF THE EVENT ACROSS SOME OF THE INTERIOR. BOTH THE ECMWF AND GFS OPERATIONAL RUNS DEPICT A STRONG LOW LEVEL JET AT 925 MB OF 70+ KT. DEPENDING UPON MIXING POTENTIAL...THIS COULD RESULT IN STRONG WINDS ACROSS THE SE COASTAL PLAIN SOMETIME ON SAT...PROBABLY AFTERNOON. A STRONG LOW LEVEL JET COULD ALSO SIGNAL SIGNIFICANT QPF...BUT THE EVENT IS TOO FAR OUT TO HAVE MUCH CONFIDENCE IN RAINFALL AMOUNTS. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. THROUGH 00Z...HIGH CONFIDENCE. GENERALLY VFR WITH CLOUD BASES 3500-4000 FEET AND 10 THOUSAND FEET. AN MVFR LAYER AROUND 2500 FEET MOVED THROUGH THE BERSHIRES INTO THE CT VALLEY AND SHOULD DISSIPATE BY EVENING. TONIGHT...MODERATE-HIGH CONFIDENCE. STILL LOTS OF CLOUDS UPSTREAM AND FORECAST MODELS SUGGEST CLOUDS WILL LINGER THROUGH MIDNIGHT BEFORE CLEARING. VFR. MONDAY AND MONDAY NIGHT...HIGH CONFIDENCE. VFR. NORTHWEST WINDS GUSTING 15-20 KNOTS MONDAY MIDDAY AND AFTERNOON. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...TUESDAY THROUGH THURSDAY... MODERATE TO HIGH CONFIDENCE OF MAINLY VFR THROUGH THE PERIOD. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH MONDAY/...MODERATE TO HIGH CONFIDENCE. THIS AFTERNOON...A MARGINAL SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL WATERS EXCEPT FOR BOSTON HARBOR AND NARRAGANSETT BAY. WE COULD SEE SW WIND GUSTS TO AROUND 25 KT EARLY AFTERNOON... FOLLOWED BY A SHIFT TO THE W AND WNW LATER THIS AFTERNOON AT THE SAME SPEEDS. SEAS SHOULD BE BUILDING FROM 3 FT UP TO 5 OR 6 FT ON THE OUTERMOST WATERS LATER THIS AFTERNOON. TONIGHT...WINDS DIMINISH AND SEAS SUBSIDE. HOWEVER A SMALL CRAFT ADVISORY WILL REMAIN POSTED FOR THE SOUTHEASTERN WATERS UNTIL ABOUT 1 AM BECAUSE THE 5 FT SEAS WILL BE SLOWEST TO SUBSIDE IN THOSE AREAS. MONDAY...NORTHWEST WINDS 10 TO 15 KT WITH GUSTS TO 20 KT OFF THE NORTHEAST MA COAST. SEAS GENERALLY 3 TO 4 FT OVER THE OUTER WATERS. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY... MODERATE TO HIGH CONFIDENCE. MON NIGHT THROUGH WED NIGHT...EXPECT WINDS AND SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS. THU...W WIND WILL LIKELY INCREASE ABOVE SMALL CRAFT ADVISORY THRESHOLDS ALL WATERS WITH A CHANCE OF GALE FORCE GUSTS OVER AT LEAST THE OUTER WATERS. ALTHOUGH THIS OUTLOOK GOES ONLY TO THU...THE HWO IS FOR 7 DAYS. WILL MENTION A RISK OF SOUTHERLY GALES ACROSS THE WATERS ON SAT IN THE HWO. TYPICALLY, AN INVERSION AT THIS TIME OF YEAR LIMITS HOW MUCH MOMENTUM IS MIXED TO THE SEA SURFACE IN A SOUTHERLY GRADIENT. HOWEVER...GIVEN A SIGNAL OF 70+ KT AT 925 MB...THINK THERE IS A CHANCE OF MIXING WINDS STRONG ENOUGH TO RESULT IN POSSIBLE GALE FORCE GUSTS ACROSS THE OUTER WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ231>235-237-250-251. SMALL CRAFT ADVISORY UNTIL 1 AM EST MONDAY FOR ANZ254>256. && $$ SYNOPSIS...WTB/THOMPSON NEAR TERM...WTB SHORT TERM...WTB LONG TERM...THOMPSON AVIATION...WTB/THOMPSON MARINE...WTB/GAF/THOMPSON

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.