Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 251740 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 140 PM EDT WED MAR 25 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE EAST OF NEW ENGLAND TODAY. MILDER AIR RETURNS AS LOW PRESSURE AND ITS ASSOCIATED WARM FRONT PUSH INTO THE NORTHEAST. THIS SYSTEM WILL BRING PERIODS OF LIGHT RAIN TO THE AREA THIS AFTERNOON THROUGH THURSDAY...WITH A TRANSITION TO A MIX OF RAIN AND SNOW THURSDAY NIGHT INTO FRIDAY AS A COLD FRONT TRACKS THROUGH. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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AS OF 140 PM EDT WEDNESDAY...HIGH PRESSURE CONTINUES TO SLIDE INTO THE ATLANTIC AS A WARM FRONT APPROACHES FROM THE SOUTHEAST WITH LIGHT RAIN SHOWERS. WITH 15 TO 30 DEGREE TEMPERATURE DEWPOINT SPREADS ACROSS THE NORTH COUNTRY, IT WILL TAKE TIME FOR THE PRECIPITATION TO MOVE INTO THE REGION AND THEN SATURATE THE AIR. SO HAVE PUSHED INCREASE OF POPS BY 2-3 HOURS. WIND GUSTS WILL CONTINUE TO DEVELOP THIS AFTERNOON WITH LACK OF PRECIPITATION STABILIZING THE ATMOSPHERE. SO EXPECT SOUTHERLY WINDS OVER MOST OF THE AREA AT 10-15KTS WITH GUSTS UP TO 30KTS. EXCEPTION IS IN THE ST LAWRENCE VALLEY WHERE SOME CHANNELING FROM THE NE IS OPPOSITE FLOW ALOFT WITH STABLE LAYER AND COOLER TEMPERATURES.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... AS OF 345 AM EDT WEDNESDAY...LOW PRESSURE TRACKING TO OUR NORTH MAKES ITS WAY ACROSS QUEBEC TONIGHT. THE WARM FRONT WILL LIFT NORTH OF THE CANADIAN BORDER THIS EVENING AS A STRONG MID-LEVEL JET AND DRY SLOT SHIFT INTO THE REGION. SO PRECIPITATION CHANCES WILL DECREASE THROUGH THE NIGHT BUT WE COULD SEE SOME SPOTTY DRIZZLE HERE AND THERE IN THE WARM SECTOR WITH LOW TEMPERATURES IN THE 30S. COULD SEE A FEW AREAS AROUND THE FREEZING MARK SO SOME SLICK SPOTS ON THE ROADWAYS EARLY THURSDAY MORNING ARE POSSIBLE. PRECIPITATION CHANCES INCREASE ONCE AGAIN DURING THURSDAY AS A SECOND STRONGER TROUGH DIGS INTO THE GREAT LAKES WITH A NEW SURFACE LOW LIFTING NORTHEAST FROM THE OHIO RIVER VALLEY INTO THE NORTHEAST THURSDAY AFTERNOON AND TO THE GULF OF MAINE BY FRIDAY MORNING. RAINFALL SHOULD BE RATHER WIDESPREAD BY THURSDAY AFTERNOON. WITH PRECIPITABLE WATER VALUES OF 0.75 TO 1 INCH EXPECTED ALONG WITH GOOD FORCING AND LIFT INDICATED FOR THE AFTERNOON...RAINFALL AMOUNTS ARE EXPECTED TO EXCEED A HALF INCH. TEMPS WILL REMAIN MILD WITH HIGHS IN THE 40S. SURFACE COLD FRONT SHIFTS THROUGH THURSDAY NIGHT WITH A TRANSITION TO A MIX OF RAIN AND SNOW WITH MAINLY SNOW OVER THE NORTHERN MOUNTAINS...THOUGH PRECIPITATION WILL BEGIN TO TAPER OFF AFTER MIDNIGHT. LIGHT ACCUMULATIONS OF A DUSTING TO AN INCH ARE POSSIBLE WITH LOWS FALLING BACK INTO THE UPPER 20S TO LOWER 30S. SNOW OR RAIN SHOWERS WILL CONTINUE FRIDAY IN LINGERING MOISTURE BEHIND COLD FRONT AS POSITIVELY TILTED UPPER TROUGH AND ASSOCIATED VORT PROVIDE LIFT. PRECIPITATION MAINLY SNOW ACROSS NORTHERN YORK AND THE HIGHER TERRAIN OF VERMONT WHERE HIGHS WILL BE ONLY IN THE LOWER 30S. MORE OF A MIX EXPECTED IN THE VALLEYS OF VERMONT WITH HIGHS 35 TO 40. WITH THE EXPECTED RAINFALL AND 36-48 HOURS OF ABOVE FREEZING TEMPERATURES WE`LL LIKELY SEE SOME MELTING OF THE SNOWPACK WHICH MAY RESULT IN SOME ICE MOVEMENT...ESPECIALLY IN OUR SOUTHERN RIVERS. FOR MORE ON THAT SEE OUR HYDRO SECTION BELOW. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... AS OF 345 AM EDT WEDNESDAY...GENERALLY QUIET UNDER HIGH PRESSURE THROUGH THE WEEKEND WITH SLIGHT CHANCES FOR SNOW ON FRIDAY AND INCREASING CHANCES FOR RAIN/SNOW SHOWERS ON MONDAY THROUGH TUESDAY MORNING. SATURDAY... ANY LINGERING SNOW SHOWERS FROM FRIDAY NIGHT WILL COME TO AN END SATURDAY MORNING AS A DRY SLOT FROM THE UPPER LEVEL TROUGH WILL PUSH INTO THE REGION. HIGH PRESSURE WILL BUILD IN AT THE SURFACE LEADING TO COLD TEMPS AND CLEARING SKIES OVER THE NORTH COUNTRY. EXPECT NORTH WESTERLY WINDS AT THE SURFACE WITH TEMPS LIKELY IN THE UPPER 20S ACROSS THE REGION BEHIND THE COLD FRONT. OVERNIGHT LOWS ON SATURDAY NIGHT WILL DROP INTO THE MID TEENS IN THE CHAMPLAIN AND SAINT LAWRENCE VALLEYS AND INTO THE SINGLE DIGITS ON THE EASTERN SLOPES OF THE GREENS AND IN THE ADIRONDACKS. SUNDAY... BY 06Z SUNDAY MORNING THE CONSENSUS OF AVAILABLE GUIDANCE FINALLY PUSHES THE UPPER LEVEL TROUGH THROUGH THE REGION AND THE SURFACE HIGH PRESSURE SYSTEM CENTERED TO THE SOUTH OVER THE CAROLINA`S WILL HAVE A WEAK GRASP OVER THE REGION. BOTH THE ECMWF AND THE GFS DEPICT A LOW PRESSURE SYSTEM LOCATED JUST TO THE WEST OF THE GREAT LAKES SLOWLY DRIFTING TO THE EAST. THE PRESSURE GRADIENT BETWEEN THE HIGH PRESSURE TO THE SOUTH AND THE HIGH TO THE NORTHWEST WILL CAUSE THE WINDS LOCALLY TO SHIFT FROM WESTERLY TO MORE WARMER SOUTHERLY FLOW LATER IN THE AFTERNOON. THAT WILL BRING MODERATING TEMPERATURES TO THE REGION AND WE SHOULD WARM INTO THE UPPER 30`S TO NEAR 40 UNDER PARTLY CLOUDY SKIES. MONDAY... SIMILAR TO YESTERDAY THE GENERAL IDEA IS THAT THERE WILL BE SOME SORT LOW PRESSURE SYSTEM TRACKING THROUGH SOUTHERN CANADA JUST NORTH OF THE GREAT LAKES. THE DIFFERENCES BETWEEN THE TWO MAIN LONG RANGE GUIDANCE LEAVES VERY LITTLE WITH REGARDS TO CONFIDENCE IN AN EXACT SOLUTION. HOWEVER BOTH MODELS SHOW RAIN/SNOW SHOWERS OVERSPREADING THE FORECAST REGION ON MONDAY. THE LACK OF CONSISTENCY IN THE STRUCTURE/INTENSITY OF THE SYSTEM LEAVES A LOT TO BE DESIRED SO THE FORECAST IS A BLEND OF THE GFS AND ECMWF. RIGHT NOW THE GFS IS MORE PROGRESSIVE AND IS RUNNING ABOUT 12 HOURS FASTER THAN THE ECMWF. I TRENDED THE FORECAST MORE TOWARDS THE SLOWER ECMWF BRINGING IN HIGH CHANGE POPS (45-55%) BETWEEN 12-18Z ON MONDAY. EXPECT INITIALLY FOR THE SHOWERS TO BE SNOW SHOWERS BEFORE TRANSITIONING IN THE AFTERNOON TO RAIN SHOWERS AS THE WARMER SOUTHERLY AIR FILTERS INTO NEW ENGLAND. AT THIS POINT, I`M REALLY IN WAIT AND SEE MODE WITH REGARDS TO HOW THE EVENT WILL EVOLVE. THE MODELS AREN`T REAL CONSISTENT ON HOW THE RAIN/SNOW SHOWERS END AS THE GFS SHOWS A SECONDARY SHORTWAVE DROPPING IN FROM CANADA AND THE ECMWF PICKS UP SPEED OF THE LOW AND QUICKLY EXISTS THE REGION INTO THE CANADIAN MARITIMES. SO I`LL CONTINUE THE INHERITED CHANCE TO SLIGHT CHANCE THROUGH TUESDAY EARLY MORNING. TEMPS MONDAY WILL BENEFIT FROM THE WARMER CYCLONIC SOUTHERLY FLOW AHEAD OF THE LOW PRESSURE SYSTEM AND WILL LIKELY BE NEAR CLIMO WITH MAX TEMPS IN THE MID TO LOW 40S WITH LOWS IN THE UPPER 20S. TUESDAY... AS PREVIOUSLY MENTIONED THE TWO DIVERGING SOLUTIONS LEAVE PLENTY TO BE DESIRED IN THE EVOLUTION OF THE SYSTEM. BOTH MODELS SHOW A WEAK COLD FRONT WILL CROSS THROUGH THE FORECAST REGION AS THE DISTURBANCE DRIFTS THROUGH THE NORTH COUNTRY. THIS WILL LEAD TO MORE WESTERLY WINDS AND A RETURN OF BELOW NORMAL TEMPS IN THE UPPER 30`S WITH OVERNIGHT LOWS IN THE MID 20S TO MID TEENS OVER THE NORTHEAST KINGDOM IN VERMONT. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... THROUGH 18Z THURSDAY...VFR CONDITIONS WILL PREVAIL UNTIL A WARM FRONT BRINGS A CHANCE FOR SHOWERS AND MVFR CEILINGS/VISIBILITIES. WINDS HAVE STARTED TO PICK UP AHEAD OF THE APPROACHING FRONT. EXPECT THE SHOWERS TO ADVANCE FROM SOUTHWEST TO NORTHEAST ACROSS THE AREA...MSS/SLK/RUT BEGINNING 19-20Z THEN IN THE CHAMPLAIN VALLEY BETWEEN 20-22Z. THE SHOWERS WILL PRODUCE GUSTY WINDS (SOUTHERLY 10-15KTS GUSTING TO 20-25) AND WILL BRING A CHANCE FOR REDUCED VISIBILITIES AS THE RAIN FALLS. BEHIND THE WARM FRONT BY 00Z EXPECT CEILINGS TO BEGIN TO COME DOWN TO AROUND MVFR/LOW VFR AT 2.5-3.5KFT. LLWS IS STILL A CONCERN AS THE WARM AIR ADVECTION WITH THE FRONT WILL BRING DECENTLY STRONG WINDS DOWN TO 2000 FT HOWEVER THAT WILL BE MORE LOCALIZED OVER THE HIGHER TERRAIN AND NOT AT THE TAF SITES. CEILINGS REMAIN DURING THE DAYTIME HOURS THURSDAY...AND SHOWERS ONCE AGAIN APPROACH AROUND 18Z. OUTLOOK 18Z THURSDAY THROUGH SUNDAY... 18Z THURSDAY - 12Z FRIDAY...VFR DETERIORATING TO PERIODS OF MVFR WITH BRIEF IFR FLIGHT CONDITIONS UNDER RAIN/SNOW SHOWERS AS A LOW PRESSURE SYSTEM BRINGS A GOOD CHANCE FOR MEASURABLE PRECIP TO THE REGION. 12Z FRIDAY - 00Z SUNDAY...MIX OF VFR AND MVFR WITH SCATTERED SNOW SHOWERS POSSIBLE. 00Z SUNDAY - 00Z MONDAY...VFR CONDITIONS UNDER RIDGE OF HIGH PRESSURE. 00Z MONDAY - TUESDAY...MVFR POSSIBLE IN SHOWERS. && .HYDROLOGY... AS OF 345 AM EDT WEDNESDAY...THE PRIMARY HYDRO ISSUE IS THE POTENTIAL FOR ICE BREAKUP AND SUBSEQUENT ICE JAMS. PERIOD OF ABOVE FREEZING TEMPERATURES WILL RELEASE SNOW MELT, AND WHEN COMBINED WITH THURSDAY RAINFALL WILL PRODUCE WITHIN BANK RISES ON RIVERS. RAIN THAT ARRIVES WITH WARM AIR ADVECTION TONIGHT WILL BE ABSORBED BY COLD SNOWPACK WITH LITTLE IMPACT ON RIVERS. SOUTH WINDS AND INCREASING DEWPOINTS WILL BEGIN MELT OF SOME SNOW ON THURSDAY, WITH HYDRO FORECAST MODELS SHOWING THREE QUARTERS TO AROUND AN INCH OF SNOWMELT ALONE THROUGH FRIDAY MORNING. RAINFALL ARRIVING LATE THURSDAY AND THURSDAY NIGHT IS THE SECOND FACTOR IN ICE BREAKUP POTENTIAL. SOME UNCERTAINTY, AS ALWAYS, INTRODUCED BY SPREAD IN MODEL RAINFALL FORECAST. BLEND OF MODELS INDICATES 0.50 TO 0.75 INCHES OF RAIN IN 18Z THURSDAY TO 06Z FRIDAY TIMEFRAME, AND QPF INCORPORATED IN RIVER FORECASTS LEAN TOWARDS THE HIGHER AMOUNTS. FORECAST RIVER RISES OF 4 TO 6 FEET WOULD BE SUFFICIENT TO BREAK UP OUR EXISTING RIVER ICE THAT IS 1 TO 1.5 FEET THICK. EVEN SCALING BACK PRECIP FORECASTS TO SOME OF THE LESSER AMOUNTS IN NAM AND ECMWF WILL PRODUCE RISES UP TO 3 FEET WHEN COMBINED WITH SNOWMELT RUNOFF, WHICH IS MARGINALLY ABLE TO BREAK UP OUR ICE COVERAGE. MAIN THREAT FOR ICE BREAKUP AND JAMS IS IN VERMONT FROM THE WINOOSKI BASIN SOUTHWARD, AS WELL AS ESSEX COUNTY NY. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...RJS NEAR TERM...KGM SHORT TERM...RJS LONG TERM...DEAL AVIATION...DEAL/NEILES HYDROLOGY...HANSON/RJS

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