Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 290551 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 1251 AM EST SAT NOV 29 2014 .SYNOPSIS... SURFACE HIGH PRESSURE ACROSS SOUTHERN CANADA WILL BUILD OVER THE NORTH COUNTRY TONIGHT...RESULTING IN COLD TEMPERATURES AND CLEARING SKIES. TEMPERATURES WILL DROP TO NEAR ZERO IN THE COLDER MOUNTAINS VALLEYS TO UPPER TEENS IN THE CHAMPLAIN VALLEY. A WARM FRONT WILL INCREASE THE CLOUDS ON SATURDAY WITH LIGHT SNOW ARRIVING BY AFTERNOON. A DUSTING TO 2 INCHES OF SNOW ACCUMULATION IS POSSIBLE WITH TEMPERATURES REBOUNDING TO ABOVE NORMAL LEVELS BY SUNDAY. && .NEAR TERM /UNTIL 7 AM THIS MORNING/... AS OF 921 PM EST FRIDAY...FORECAST STILL IN GOOD SHAPE FOR REMAINDER OF THE NIGHT WITH LINGERING NRN MTN SHSN/FLURRIES SLOWLY COMING TO AND END LEAVING VARIABLY CLOUDY/PTLY CLOUDY SKIES ACROSS THE AREA. SOME NATURAL VARIABILITY STARTING TO CROP UP IN HOURLY T/TD OBSERVATIONS...BUT A QUICK LOOK AT FORECAST OVERNIGHT MINS STILL APPEAR MOST REASONABLE OUT OF AVAILABLE GUIDANCE SO LEFT THOSE VALUES UNCHANGED. PRIMARY ADJUSTMENT WAS TO DELAY ONSET OF PCPN ACROSS THE AREA TOMORROW...KEEPING BULK OF LIGHT SNOWS/MIXED PCPN OUT OF THE AREA UNTIL AFTER SUNSET. THIS IS IN BETTER AGREEMENT WITH NEARLY ALL MODEL RH/OMEGA PROGS AND MOS OUTPUT. STILL LOOKING AT A PERIOD OF LIGHT MIXED PCPN TOMORROW EVENING/OVERNIGHT HOWEVER SO PLEASE REFER TO PRIMARY SHORT TERM DISCUSSION BELOW DESCRIBING DYNAMICAL FORCING/REASONING ETC. HAVE A GREAT NIGHT. PRIOR NEAR TERM DISCUSSION FROM 628 PM EST FRIDAY... FORECAST REMAINS MORE OR LESS ON TRACK AS OF EARLY EVENING. ADJUSTED SKY COVER AND T/TD DATA TO MATCH CURRENT TRENDS. SNOW SHOWERS/FLURRIES CONTINUE OVER THE NEXT FEW HOURS THEN WANE/END. POTL BUST ON TEMPERATURES OVERNIGHT GIVEN FRESH SNOW COVER AND CLEARING SKIES...BUT WARM THERMAL ADVECTION- DRIVEN MID CLOUDS ARRIVE LATE SO TOUGH CALL. VALUES RANGING FROM 5-15 ABOVE WITH A FEW UNLUCKY SPOTS AROUND ZERO STILL LOOK REASONABLE ATTM. && .SHORT TERM /7 AM THIS MORNING THROUGH SUNDAY NIGHT/... AS OF 340 PM EST FRIDAY..A LARGE SWING IN TEMPS ARE EXPECTED FROM A COLD MORNING ON SATURDAY TO MUCH ABOVE NORMAL VALUES BY SUNDAY...ALONG WITH A PERIOD OF LIGHT ACCUMULATING SNOWFALL. THE COMBINATION OF STRONG LLVL WAA/FGEN FORCING FROM 850 TO 700MB...GOOD RIBBON OF RH >80%...AND SOME 5H ENERGY WL PRODUCE A BAND OF SNOW ACRS OUR CWA ON SAT AFTN INTO SAT EVENING. SNOW ACCUMULATIONS WL RANGE FROM A DUSTING TO 2 INCHES WITH QPF < 0.10". USING THE RH FIELDS AND COMPOSITE REFLECTIVITY PROGGS PLACES THE SNOW BAND ACRS THE SOUTHERN SLV/WESTERN DACKS BTWN 18Z- 21Z SAT...INTO THE NORTHERN DACKS AND CPV AROUND 00Z SUNDAY...AND IMPACTING CENTRAL/NORTHERN VT BTWN 00Z-06Z SUNDAY. SOUNDINGS SHOW GOOD RH/OMEGA AND FAVORABLE SNOW GROWTH ALL INTERSECTING EACH OTHER...SUPPORTING BIG FLAKE SIZE. EXPECTING ONLY A 1 TO 3 HOUR WINDOW OF PRECIP LATE SAT AFT INTO SAT NIGHT ASSOCIATED WITH THIS WARM FRNT FEATURE. PROGGED 85H TEMPS REMAIN BTWN -8C AND -10C ON SAT...BUT WARM TO NEAR 0C BY 12Z SUNDAY. THIS LLVL WAA COMBINED WITH INCREASED SOUTHWEST WINDS WL RESULT IN TEMPS WARMING OVERNIGHT SAT INTO SUNDAY...WITH COLDEST READINGS IN THE DEEPER VALLEYS OF CENTRAL/EASTERN VT...WHERE THE COLD AIR REMAINS TRAPPED. WL MENTION HIGHS MAINLY IN THE 20S TO L30S ON SATURDAY...WITH LOWS RANGING FROM THE UPPER TEENS NEK/EASTERN VT TO NEAR 30F CPV/SLV...WITH TEMPS WARMING TWD 12Z SUNDAY. WINDS WL INCREASE SHARPLY AFT 00Z SUNDAY...ESPECIALLY MTN SUMMITS ASSOCIATED WITH 925MB TO 850MB JET OF 40 TO 50 KNOTS...HELPING TO ADVECT THE WARMER AIR INTO OUR CWA. FOR SUNDAY...THICKNESS AND LLVL TEMPS INCREASE QUICKLY UNDER BOARD SW FLW...WHILE BEST 850 TO 500MB RH IS NORTHEAST OF OUR CWA BY 12Z. HOWEVER...SOUNDINGS SHOW PLENTY OF MOISTURE BTWN SFC AND 850MB ON SUNDAY...ALONG WITH WEAK UVVS FIELDS...SO THINKING AREAS OF DRIZZLE WL BE LIKELY...WITH SOME FREEZING DRIZZLE POSSIBLE BTWN 1800 FEET AND 2500 FT THRU 18Z SUNDAY...BEFORE ENTIRE THERMAL PROFILE WARMS ABOVE 0C. ALSO...HIGH RESOLUTION MODEL DATA SHOWS POTENTIAL FOR COLD AIR TO GET TRAPPED IN THE DEEPER VALLEYS OF VT ON SUNDAY MORNING...RESULTING IN AREAS OF LIGHT FREEZING DRIZZLE. ICE ACCUMULATION WL BE MINOR...WITH NO SIGNIFICANT IMPACTS ANTICIPATED ATTM. TEMPS BY SUNDAY AFTN WL WARM INTO THE 40S SLV/CPV WITH MID/UPPER LVL NEK/MTNS. A VERY WARM NIGHT EXPECTED ON SUNDAY NIGHT...WITH TEMPS HOLDING STEADY IN MOST LOCATIONS WITH BREEZY SOUTHWEST WINDS....AHEAD OF SHARP SFC BOUNDARY. THIS BOUNDARY WL INCREASE THE CHCS FOR MAINLY RAIN SHOWERS AFT 06Z...ALONG WITH FALLING TEMPS ACRS NORTHERN NY TWD 12Z MONDAY. PRECIP AMOUNTS WL BE LIGHT ASSOCIATED WITH SFC COLD FRNT THRU 12Z MONDAY. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 340 PM EST FRIDAY...LOOKS LIKE A WEEK OF FAST-CHANGING WEATHER. 12Z GUIDANCE SUITE IN DECENT AGREEMENT UP TO WEDNESDAY, THEN THE GFS AND ECMWF GO THEIR OWN WAY. HAVE STUCK WITH A BLEND FOR MONDAY-WEDNESDAY, AND LEANED A BIT MORE TOWARD THE ECMWF AFTER THAT. RAMBLING THOUGHTS FOR EACH DAY ARE BELOW: MONDAY: SHARP COLD FRONT WILL QUICKLY PUSH EAST OF THE FORECAST AREA BY LATE MORNING (IF NOT A BIT EARLIER). ASSUMING WE`VE GOT THE TIMING OF THE FRONTAL PASSAGE CORRECT, HIGH TEMPERATURES WILL OCCUR BETWEEN 6AM-10AM, AND THEN FALL. SO EVEN THOUGH THE FORECAST WORDS MAY SAY "HIGH OF 40", THE REALITY IS THAT MOST OF THE DAY WILL BE IN THE 20S! COULD BE A BRIEF PERIOD OF GUSTY WINDS WITH THE FRONTAL PASSAGE AND JUST BEHIND IT AS STRONG COLD AIR ADVECTION COMMENCES. NOT A LOT OF MOISTURE WITH THE FRONT, BUT SHOULD BE A FEW SHOWERS AROUND. INITIALLY RAIN SHOWERS, BUT WILL TURN QUICKLY TO SNOW SHOWERS -- AND BY EARLY AFTERNOON BE FOCUSEDMORE ACROSS THE HIGHER TERRAIN. PERHAPS A DUSTING IN LOWER ELEVATIONS AND AN INCH OR SO IN THE HIGHER TERRAIN. VERY PROGRESSIVE/FAST FLOW PATTERN. HIGH PRESSURE QUICKLY BUILDS IN OVERNIGHT AND SHOULD RESULT IN CLEAR SKIES. THE HIGH PRESSURE DOES HAVE IT`S SOURCE IN FAR NORTHWEST CANADA AND WILL BE ASSOCIATED WITH 925MB TEMPERATURES OF -12 TO -18C. THIS MEANS TEMPERATURES GENERALLY IN THE 0F TO +15F RANGE HERE AT GROUND LEVEL. BY THE WAY, THE PRESSURE IN THE CENTER OF THAT HIGH WILL BE ABOUT 1044MB (30.82"). TUESDAY: STRONG HIGH PRESSURE BEGINS TO PUSH TO OUR EAST, BUT KEEPS ITS INFLUENCE OVER US FOR MOST OF THE DAY. WITH 925MB TEMPERATURES STILL IN THE -12 TO -15C RANGE, HIGHS EVERYWHERE WILL BE SUB-FREEZING. PERHAPS JUST MID 20S FOR THE "WARMER" VALLEYS. THIS IS ABOUT 10-12 DEGREES BELOW NORMAL. SOUTHWEST RETURN FLOW BEGINS TUESDAY NIGHT AS THE HIGH MOVES EAST. IN GENERAL, WE`LL PROBABLY SEE A QUICK FALL OF TEMPERATURES EARLY IN THE EVENING AND THEN STEADY/SLOW RISE LATER AT NIGHT. TIMING OF THE RETURN FLOW THIS FAR OUT IS QUITE DIFFICULT, SO JUST WENT WITH MODEL BLEND FOR LOWS. SO GENERALLY 10-20F, COLDEST IN THE NORTHEAST KINGDOM. RATHER HIGH POTENTIAL FOR TEMPERATURE BUSTS IN THIS FORECAST. WEDNESDAY: LOW PRESSURE MOVES QUICKLY ACROSS THE GREAT LAKES WITH A STRONG LOW LEVEL SOUTHERLY JET OF 40-50KT DEVELOPING. THIS STRONG JET WILL BRING MUCH WARMER AIR ALOFT -- AND THUS MAKE FOR ISSUES WITH PRECIPITATION TYPE. LIKED THE ECMWF DEPICTION OF THE TEMPERATURES ALOFT (925MB TEMPERATURES +1 TO +3C BY 18Z), AND THUS EXPECT INITIAL BOUT OF LIGHT SNOW TO TURN INTO A BRIEF PERIOD OF LIGHT SLEET BEFORE TURNING INTO A BOUT OF LIGHT RAIN. CAN`T RULE OUT SOME ISOLATED LIGHT FREEZING RAIN IN PARTS OF EASTERN VERMONT WHERE COLD AIR REMAINS STUCK IN VARIOUS NOOKS AND CREVICES. SURFACE PRESSURE PATTERN SHOWN BY BOTH THE ECMWF AND GFS INDICATE THE LIKELIHOOD OF COLD AIR DAMMING DOWN ALONG THE NEW ENGLAND COAST. ALL OF THIS TRANSITION SHOULD HAPPEN IN 6-8 HOURS TIME. HIGHS SHOULD RANGE FROM THE MID 30S TO LOWER 40S IN THE VALLEYS. COULD BE A LITTLE BREEZY IN THE CHAMPLAIN & ST LAWRENCE VALLEYS WITH THE STRONG LOW LEVEL JET, BUT PRECIPITATION SHOULD STABILIZE THE BOUNDARY LAYER AND KEEP THE STRONGEST OF THE WINDS FROM FULLY MIXING TO THE SURFACE. THOUGH THIS WILL BE A MIX OF WINTRY PRECIPITATION EVENT, IT DOES LOOK LIKE OVERALL PRECIPITATION AMOUNTS WILL BE LESS THAN 1/3", SO NOT ANTICIPATING ANYTHING MAJOR. THE "WARM UP" WILL BE SHORT LIVED. THE FAST MOVING LOW WILL PASS BY TO OUR NORTH WEDNESDAY EVENING, DRAGGING A COLD FRONT THROUGH. THUS TEMPERATURES FALL BACK BELOW FREEZING. ANY REMAINING PRECIPITATION WILL END AS SNOW. THURSDAY/FRIDAY: AS MENTIONED ABOVE, LIKED THE ECMWF SOLUTION OVER THE GFS. IN THIS SCENARIO, ANOTHER FAIRLY STRONG (BUT ONLY 1035MB THIS TIME) HIGH QUICKLY BUILDS IN AND PUSHES THE COLD FRONT WELL TO THE SOUTH. LEADS TO A DRY THURSDAY, AND MOST OF FRIDAY. HOWEVER WITH THE HIGH PUSHING EAST DURING THE DAY FRIDAY, OUR FLOW AGAIN TURNS SOUTHERLY AND STARTS BRINGING UP THE MOISTURE FROM THE FRONT TO THE SOUTH BY THE AFTERNOON. FOR THAT REASON, I DID PUT IN SOME LOW POPS (20-30%) AND PAINTED IN MOSTLY CLOUDY SKIES. TO CONTRAST, THE GFS NEVER PUSHES THAT WEDNESDAY COLD FRONT TOO FAR AWAY. THE HIGH IT BRINGS IN FOR THURSDAY IS TO OUR NORTH, WITH SOUTHWEST FLOW ALOFT OVERRUNNING THE FRONT RESULTING IN CLOUDS AND LIGHT PRECIPITATION (IN THE FORM OF A WINTER MIX) THURSDAY AND FRIDAY. LOOKING AT THE VARIOUS 12Z GFS ENSEMBLE MEMBERS, THERE WAS NOT ANY CONSISTENCY WITH THE OPERATIONAL RUN, SO WHAT THAT ALL MEANS IS LOW CONFIDENCE IN THE FORECAST TO END THE WEEK. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... THROUGH 12Z SUNDAY...VARIABLY CLOUDY SKIES ARE EXPECTED THROUGH THE TAF PERIOD...BUT CEILINGS WILL PREDOMINANTLY BE VFR THROUGH 01Z SUNDAY. TRENDING OVERCAST THIS EVENING WITH SCATTERED SNOW SHOWERS BEGINNING AFTER 01Z SUNDAY. MAJORITY OF THE ACTIVITY WILL BE LIGHT. CARRIED 5-6SM -SHSN FOR ALL TAF SITES AT THIS POINT. HIGH PRESSURE IN PLACE PROVIDING LIGHT AND VARIABLE WINDS TO START THE PERIOD. SURFACE HIGH DRIFTS EAST OF NEW ENGLAND THIS EVENING AND OVERNIGHT WITH INCREASING SOUTHERLY GRADIENT WINDS EXPECTED DURING THE OVERNIGHT PERIOD. LOCALIZED CHANNELING IN THE CHAMPLAIN VALLEY WILL BRING SOUTH WINDS AROUND 15-18 KTS WITH GUSTS 25-30 KTS AT BTV AFTER 03Z SUNDAY. OUTLOOK 12Z SUNDAY THROUGH WEDNESDAY...GENERALLY VFR DURING SUNDAY AND EARLY SUNDAY NIGHT. A COLD FRONT SHIFTING EWD ACROSS THE AREA 06-12Z MONDAY COULD BRING MVFR SCATTERED RAIN SHOWERS...PERHAPS ENDING AS LIGHT SNOW SHOWERS OR FLURRIES MONDAY MORNING (BEST CHANCE OF ANY SNOW SHOWERS WILL BE AT SLK/MPV MONDAY MORNING). HIGH PRESSURE RETURNS BRINGING GENERALLY VFR WEATHER CONDITIONS 18Z MONDAY THROUGH 06Z WEDNESDAY. NEXT WARM FRONTAL BOUNDARY BRINGS A CHANCE OF RAIN OR SNOW SHOWERS 06Z WED THROUGH 00Z THURSDAY...WITH INTERVALS OF MVFR CONDITIONS POSSIBLE. THE MAJORITY OF THIS ACTIVITY IS EXPECTED TO BE LIGHT. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...TABER NEAR TERM...JMG SHORT TERM...TABER LONG TERM...NASH AVIATION...BANACOS

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