Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 231146 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 646 AM EST TUE DEC 23 2014 .SYNOPSIS... A MAJOR WARMUP IS EXPECTED ACROSS THE NORTH COUNTRY BEGINNING TODAY. AN INITIAL WARM FRONT BRINGS MIXED WINTRY PRECIPITATION THIS MORNING...FOLLOWED BY PERIODS OF LIGHT RAIN THIS AFTERNOON THROUGH TONIGHT. A STRONGER LOW PRESSURE SYSTEM FORMING IN THE OHIO VALLEY WEDNESDAY WILL ALLOW FOR A NORTHWARD SURGE OF GULF MOISTURE AND WARMER TEMPERATURES. TEMPERATURES WILL REACH THE MID 40S TO LOWER 50S FOR MOST SPOTS CHRISTMAS EVE DAY AND CHRISTMAS DAY. HOWEVER...PERIODS OF MODERATE TO BRIEFLY HEAVY RAIN CAN ALSO BE EXPECTED...MAINLY LATE CHRISTMAS EVE DAY INTO CHRISTMAS EVE NIGHT. GUSTY WINDS CAN ALSO BE EXPECTED...MAINLY OVER THE HIGHER TERRAIN AND ACROSS THE ST. LAWRENCE VALLEY. RAINFALL AMOUNTS OF 1 TO 2 INCHES COMBINED WITH SNOWMELT WILL CAUSE POOR DRAINAGE...FIELD...AND POSSIBLE MINOR RIVER FLOODING CHRISTMAS EVE NIGHT INTO CHRISTMAS DAY. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... AS OF 347 AM EST TUESDAY...00Z NWP GUIDANCE WAS GENERALLY TOO QUICK IN WARMING TEMPERATURES EARLY THIS MORNING AWAY FROM DOWNSLOPE AREAS IMMEDIATELY WEST OF THE GREEN MTNS. NARROW ZONE OF TEMPS 34-37F FROM RUTLAND COUNTY NWD INTO ERN CHITTENDEN COUNTY...BUT GENERALLY IN THE 20S ELSEWHERE...AND EVEN A REGION OF MID TEENS ON THE NRN SLOPES OF THE ADIRONDACKS AT 08Z. INITIAL WARM FRONT AND SHORTWAVE TROUGH LIFTING NWD HAS RESULTED IN SHARP OVERRUNNING/ISENTROPIC ASCENT INTO ANTECEDENT SUBFREEZING AIR MASS. SEEING AN INITIAL PERIOD OF STEADY SNOW...WHICH WILL BE FOLLOWED BY SLEET TOWARD DAYBREAK. WITH NELY LOW-LEVEL FLOW LOCKED IN ACROSS NRN NY THIS MORNING AND COLD SFC TEMPERATURES...AM INCREASINGLY CONCERNED FOR A PERIOD OF FREEZING RAIN ACCUMULATION ACROSS OUR NRN NY ZONES BEFORE STEADY PRECIPITATION ABATES. THIS HAS WARRANTED AN EXPANSION OF THE WINTER WEATHER ADVISORY ACROSS OUR NRN NY COUNTIES (THROUGH NOON). LIKEWISE...THE VERTICAL TEMPERATURE PROFILES WARM MORE QUICKLY ALOFT ACROSS NRN NY...AND THOSE PROFILES ARE MOST FAVORABLE FOR FREEZING RAIN ACROSS NRN NY. GENERALLY LOOKING AT SEVERAL HUNDRETHS OF AN INCH OF FREEZING RAIN ACROSS NRN NY...WITH GENERALLY A COATING TO 2 INCHES OF SNOW AND SLEET ACCUMULATION FOR VERMONT. WILL DEFINITELY SEE SOME TRAVEL SLOW-DOWNS FOR THE MORNING COMMUTE...ESPECIALLY WITH LIGHT ICE ACCUMULATION IN THE ST. LAWRENCE VALLEY...PORTIONS OF THE ADIRONDACKS...AND NY SIDE OF THE CHAMPLAIN VALLEY. IT APPEARS TEMPERATURES WARM ABOVE FREEZING AREAWIDE BY 17Z...AND THIS SHOULD CEASE ANY FREEZING RAIN CONCERNS. INITIAL SHORTWAVE TROUGH PASSES BY TO OUR EAST...BUT WILL LIKELY SEE INTERVALS OF SOME LIGHTER RAINFALL FROM TIME TO TIME THROUGH THE AFTERNOON. HIGHS THIS AFTERNOON WILL GENERALLY REACH THE UPR 30S TO LOWER 40S...WARMEST IN THE SRN CHAMPLAIN VALLEY/RUTLAND COUNTY...AND ALSO ACROSS SWRN SECTIONS OF ST. LAWRENCE COUNTY. WINDS GENERALLY SE 5-10 MPH...BUT LOCALLY NELY IN THE ST. LAWRENCE VALLEY AND ADJACENT PORTIONS OF CLINTON COUNTY. && .SHORT TERM /7 PM THIS EVENING THROUGH THURSDAY/... AS OF 347 AM EST TUESDAY...DEEP MERIDIONAL MID-LEVEL TROUGH ACROSS THE CENTRAL U.S. WILL BE THE MAIN FOCUS THROUGHOUT THE SHORT-TERM FORECAST PERIOD. ASSOCIATED SFC LOW TAKING SHAPE ACROSS THE TENNESSEE VALLEY ON WEDNESDAY WILL DEEPEN RAPIDLY AS IT TRACKS NWD INTO SERN LOWER MICHIGAN DURING CHRISTMAS EVE AND THEN ACROSS SWRN QUEBEC ON CHRISTMAS MORNING. DEEP-LAYER SOUTHERLY FLOW BRINGS GULF MOISTURE AND SIGNIFICANT WARMING...WITH 850MB TEMPERATURES REACHING +10C BY 00Z THURSDAY. LIKEWISE...PW VALUES ARE EXPECTED TO REACH 1.2-1.4" ACROSS THE AREA...WHICH IS QUITE ANOMALOUS FOR MID-LATE DECEMBER. IN FACT...THE HIGHEST PW ON RECORD AT 00Z DEC 25TH AT ALB IS 1.05" AND RARELY REACHES 1.4" FOR ANY TIME FRAME IN DECEMBER...PER SPC SOUNDING CLIMATOLOGY (WHICH HAS A PERIOD OF RECORD BACK TO 1948). LOOKING AT TEMPERATURES REMAINING IN THE UPR 30S TO LOWER 40S FOR LOWS TONIGHT UNDER CLOUDY SKIES AND CONTINUED SOUTH WINDS. COULD SEE PERIODS OF LIGHT RAIN SHOWER ACTIVITY WITH CONTINUED 850-700MB WARM ADVECTION AND ASSOCIATED ASCENT. ALSO...WILL BE LOOKING FOR SOME PATCHY FOG TO FORM OVER THE SNOWPACK ESPECIALLY AFTER MIDNIGHT AS DEWPOINTS CLIMB INTO THE MID-UPR 30S. THE STRONG SYNOPTIC/QG FORCING ARRIVES WEDNESDAY AFTERNOON AND NIGHT ALONG WITH HIGHEST PW VALUES. IT IS DURING THIS TIME FRAME THAT THE HEAVIEST RAINFALL WILL LIKELY OCCUR WITH ENHANCEMENT ON S-SE FACING SLOPES WITH SLY 850MB FLOW OF 30-40 KTS. STORM TOTAL RAINFALL AMOUNTS BY CHRISTMAS MORNING WILL RANGE FROM 0.8-1.6"...WITH THE HIGHEST AMTS ALONG THE ERN SLOPES OF THE GREENS AND INTO THE ADIRONDACKS. THE LOWER END AMOUNTS (0.8-1.0") ARE EXPECTED ACROSS THE ST. LAWRENCE VALLEY AND CHAMPLAIN VALLEY. TEMPERATURES WEDNESDAY AND THURSDAY WILL REACH THE MID 40S TO LOWER 50S FOR HIGHS...AND GENERALLY REMAIN IN THE 40S FOR CHRISTMAS EVE NIGHT. FORECAST RAINFALL AMOUNTS COMBINED WITH SNOWMELT AND FROZEN GROUND CONDITIONS...INDICATES THAT THE POTENTIAL EXISTS FOR SIGNIFICANT RUNOFF. THIS WILL CAUSE SHARP RISES IN AREA STREAMS AND RIVERS WEDNESDAY AND THURSDAY. MOST OF THE FLOODING WILL LIKELY BE MINOR...AND GENERALLY RELATED TO POOR DRAINAGE AND FIELD FLOODING. ON THE MAIN-STEM RIVERS...GFS ENSEMBLE BASED RIVER STAGE GUIDANCE SUGGESTS ~50% PROBABILITIES OF MINOR RIVER FLOODING FOR THE AUSABLE AT AUSABLE FORKS AND OTTER CREEK AT CENTER RUTLAND (WITH CRESTS ON CHRISTMAS DAY). THOSE WOULD BE THE TWO BASINS MOST PRONE TO FLOODING BASED ON CURRENT TRENDS...AND WE WILL CONTINUE TO MONITOR. SURFACE OCCLUDED FRONT SWEEPING THRU CHRISTMAS MORNING WILL ALLOW THE STEADIER RAIN TO EXIT EAST OF VT BY 12-13Z. SOME LOW-LEVEL CAA AND STRONG P-GRADIENT SETS UP GUSTY SWLY WIND CONDITIONS...ESPECIALLY FOR THE ST. LAWRENCE VALLEY. COULD SEE GUSTS 40-50 MPH LOCALLY ACROSS THE ST. LAWRENCE VALLEY...AND THIS WILL ALSO NEED TO BE MONITORED. A FEW LIGHT RAIN/MOUNTAIN SNOW SHOWERS ARE POSSIBLE DURING CHRISTMAS DAY...BUT DO NOT APPEAR SIGNIFICANT AT THIS TIME. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AS OF 320 AM EST TUESDAY...GENERALLY IMPROVING CONDITIONS THURSDAY NIGHT INTO FRIDAY AS RIDGING BUILDS TO OVER THE REGION AT THE SURFACE AND ALOFT. A FEW LINGERING SNOW SHOWERS ARE POSSIBLE THURSDAY NIGHT, MAINLY IN THE NORTHEAST KINGDOM. BUT THE RIDGE WILL CREST OVER THE REGION LATE IN THE DAY FRIDAY WITH DRY WEATHER. MAX TEMPERATURES ON FRIDAY WILL BE MILD, REACHING THE M30S TO L40S. CLOUDS WILL BE INCREASING EARLY SATURDAY WITH SOUTHERLY FLOW INCREASING AS THE RIDGE SLIDES SOUTHEASTWARD INTO THE ATLANTIC. AN UPPER LEVEL TROUGH WILL BRING A CHANCE FOR PRECIPITATION LATE SATURDAY INTO SUNDAY. HOWEVER, MODEL GUIDANCE DISAGREEING ON DETAILS OF THIS WEEKEND SYSTEM. DIFFERENCES IN STRENGTH, EVOLUTION AND TRACK WILL AFFECT POSSIBLE PRECIPITATION TYPE AS WELL. BEING THAT A COLD FRONT WILL MOVE THROUGH THE AREA SOMETIME OVER THE WEEKEND, EXPECT MAINLY A RAIN MIXING TO SNOW TRANSITION. HIGH PRESSURE BEGINS TO BUILD IN FOR THE BEGINNING OF THE WORK WEEK, BUT ALOFT SEVERAL DISTURBANCES WILL MOVE OVER THE AREA...KEEPING PARTLY CLOUDY TO MOSTLY CLOUDY SKIES IN THE FORECAST WITH NOTICEABLY COLDER TEMPERATURES. MONDAY MAX TEMPERATURES ONLY REACH THE UPPER TEENS TO UPPER 20S, WITH MIN TEMPERATURES SUNDAY NIGHT AND MONDAY NIGHT IN THE SINGLE DIGITS TO UPPER TEENS. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... THROUGH 12Z WEDNESDAY...WINTRY MIX CONTINUES THIS MORNING, PRODUCING MVFR AND IFR CONDITIONS AT MOST SITES. EXPECT THE TRANSITION FROM FROZEN OR FREEZING PRECIPITATION TO ALL RAIN BETWEEN 15Z AND 18Z. AS THIS OCCURS, LIFR/IFR VISBYS WILL BECOME MVFR TO VFR WITH MORE SHOWERY CONDITIONS EXPECTED. HEADING INTO THIS EVENING, WARMER AIR OVER ANY REMAINING SNOW ON GROUND WILL LIKELY PRODUCE SOME MVFR/IFR FOG, WITH BEST CHANCES AT KSLK AND KMPV. MODELS SLOWING DOWN THE APPROACH OF LOW LEVEL JET...WITH LOW LEVEL WIND SHEAR OUT OF THE SOUTH OF 35-45 KTS POSSIBLE LATE TODAY. OUTLOOK 12Z WEDNESDAY THROUGH SATURDAY... 12Z WED-06Z THU...PERIODS OF MVFR/IFR IN RAIN. GUSTY WINDS POSSIBLE. 06Z THU-18Z THU...INITIAL MVFR/IFR DUE TO RAIN ALONG A SHARP COLD FRONTAL PASSAGE CHRISTMAS DAY, BECOMING VFR/MVFR AS FRONT CLEARS. SHARP WIND SHIFT FROM SOUTH TO WEST/NORTHWEST, WITH GUSTY WEST WINDS DEVELOPING BEHIND FRONT INTO THURSDAY AFTERNOON. 18Z THU-12Z FRI...MOSTLY VFR WITH MVFR POSSIBLE IN SCATTERED RAIN/SNOW SHOWERS. 12Z FRI ONWARD...GENERALLY VFR UNDER HIGH PRESSURE. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...WINTER WEATHER ADVISORY UNTIL 8 AM EST THIS MORNING FOR VTZ011- 012-019. NY...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NYZ026>031- 034-035-087. && $$ SYNOPSIS...BANACOS NEAR TERM...BANACOS SHORT TERM...BANACOS LONG TERM...KGM AVIATION...KGM

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