Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 270614 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 214 AM EDT SUN JUL 27 2014 .SYNOPSIS... AN ACTIVE PERIOD OF WEATHER IS EXPECTED ACROSS THE NORTH COUNTRY WITH SEVERAL ROUNDS OF SHOWERS WITH EMBEDDED THUNDERSTORMS LIKELY. FIRST ROUND ARRIVES LATE TONIGHT INTO SUNDAY...WITH ADDITIONAL SHOWERS ON MONDAY INTO TUESDAY. DAYTIME HIGH TEMPERATURES WILL BE SLIGHTLY BELOW NORMAL...WITH SLIGHTLY ABOVE NORMAL OVERNIGHT LOWS...DUE TO CLOUDS. IN ADDITION...AN INCREASE IN THE RELATIVE HUMIDITY VALUES WILL OCCUR BY SUNDAY AFTERNOON. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... AS OF 1252 AM EDT SUNDAY...GIVEN INCREASING AREAL COVERAGE OF SHOWERS PER COMPOSITE RADAR IMAGERY...I`VE ADJUSTED POPS AND WX TO REFLECT AREAL COVERAGE WORDING. MID-LEVEL SHORTWAVE TROUGH EVIDENT IN WV IMAGERY ACROSS LAKE HURON PRIMARILY RESPONSIBLE FOR THIS INCREASE IN AREAL COVERAGE OF SHOWERS NOW ACROSS NORTHERN NEW YORK. I ALSO NOTE A RATHER SOLID LINE OF HEAVIER SHOWERS AND EMBEDDED THUNDERSTORMS APPROACHING THE NORTHWESTERN SHORE OF LAKE ONTARIO - ASSOCIATED WITH A ZONE OF SLIGHTLY NEGATIVE SHOWALTER INDICES (-1 TO -2) PER 03Z RAP ANALYSES IN ADDITION TO AFOREMENTIONED MID- LEVEL SHORTWAVE. THOSE NEGATIVE SHOWALTERS ARE PROGGED TO TRANSLATE EASTWARD...LIKELY KEEPING A THUNDER THREAT GOING AS IT MOVES EAST EARLY THIS MORNING. HRRR AND WRF-ARW APPEAR TO HAVE THE BEST HANDLE ON ONGOING ACTIVITY. EXTRAPOLATION OF THE MORE SOLID LINE OF SHOWERS AND STORMS INTO ST. LAWRENCE VALLEY NEXT COUPLE HOURS...ADIRONDACKS BY THE PRE- DAWN HOURS/SUNRISE...AND CHAMPLAIN VALLEY AROUND 6-7 AM. UNTIL THEN...EXPECT SCATTERED SHOWERS TO GRADUALLY SPREAD EAST. CHANGE IN WX GRIDS ESSENTIALLY STATES SCATTERED TO NUMEROUS SHOWERS...WITH SCATTERED T-STORMS TIED TO HIGHEST POP (70-80%). OTHERWISE...MADE MOSTLY MINOR ADJUSTMENTS TO LOWS ACROSS EAST VT AND THE ADIRONDACKS. && .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY NIGHT/... AS OF 335 PM EDT SATURDAY...ACTIVE WEATHER PERIOD ANTICIPATED WITH PERIODS OF OCCASIONAL SHOWERS WITH SOME EMBEDDED THUNDERSTORMS EXPECTED. FORECAST FOCUS WILL BE TIMING OF PRECIPITATION AND POTENTIAL FOR A FEW STRONGER STORMS ON SUNDAY...IF ENOUGH INSTABILITY CAN DEVELOP. ON SUNDAY...1ST S/W ENERGY AND ASSOCIATED PRECIPITATION WILL EXIT VT BY 15Z. QUESTION WILL BE HOW MUCH CLEARING DEVELOPS ON SUNDAY AFTERNOON TO CAUSE SURFACE HEATING AND INCREASE OUR INSTABILITY PARAMETERS. MODELS VARY ON THIS GREATLY WITH THE LOCAL BTV4 SHOWING CAPE VALUES BETWEEN 1500 AND 1800 J/KG...WHILE NAM12 IS BETWEEN 1000 AND 1200 J/KG AND THE GFS VALUES RANGE FROM 800 TO 1000 J/KG...WITH ALL MODELS SUGGESTING 0 TO 6 KM SHEAR VALUES BETWEEN 30 AND 40 KNOTS ON SUNDAY AFTERNOON. THINKING ENOUGH INSTABILITY WILL DEVELOP TO PROMOTE CONVECTIVE UPDRAFTS WITH A FEW STRONGER STORMS POSSIBLE. HOWEVER...SYNOPTIC SCALE FORCING WILL BE MINIMAL AFTER MORNING S/W ENERGY EXITS OUR AREA...BUT LEFTOVER OUTFLOW BOUNDARIES AND TERRAIN WILL BE FOCUS FOR AFTERNOON SHOWERS/STORM DEVELOPMENT. WILL MENTION LIKELY POPS EASTERN/CENTRAL OUR AREA THROUGH 15Z...THEN TAPER TO CHANCE POPS WITH HIGHEST VALUES ACROSS THE MOUNTAINS. A FEW STRONGER STORMS WILL BE CAPABLE OF PRODUCING SMALL HAIL AND BRIEF GUSTY WINDS...BUT AREAL COVERAGE WILL BE LIMITED THEREFORE WILL NOT MENTION IN GRIDS...BUT WILL IN THE HAZARDOUS WEATHER OUTLOOK. PROGGED 85H TEMPS BETWEEN 12-14C ON SUNDAY WITH SOME SUN/MIXING SHOULD SUPPORT AFTERNOON HIGHS IN THE M70S MOUNTAINS/NEK TO U70S/L80S WARMER VALLEYS. FOR SUNDAY NIGHT THROUGH MONDAY NIGHT...LARGE SCALE SYNOPTIC PATTERN SHOWS A DEVELOPING FULL LATITUDE TROF ACROSS THE EASTERN CONUS...WHILE RIDGE BUILDS ACROSS THE INTER-MOUNTAIN WEST. THIS DEEP TROF WILL RESULT IN UNSETTLED WEATHER ACROSS OUR OUR AREA...WITH A WIDESPREAD WETTING RAINFALL EVENT LIKELY ON SUNDAY NIGHT INTO MONDAY. POTENT S/W ENERGY WILL DIG ACROSS THE CENTRAL GREAT LAKES ON SUNDAY EVENING AND BE LOCATED OVER SOUTHERN NEW ENGLAND BY 12Z MONDAY...WHILE A NEGATIVELY TITLED 7/5H TROF DEVELOPS. THIS ENERGY...COMBINED WITH DEVELOPING NEGATIVELY TILTED MID/UPPER LEVEL TROF AND SURFACE LOW PRES TRACKING FROM NW PA TO CENTRAL NEW ENGLAND WILL PRODUCE A MODERATE RAINFALL EVENT ACROSS OUR OUR AREA. THIS SYNOPTIC SETUP DURING THE WINTER MONTHS WOULD HAVE RESULTED IN A NICE ACCUMULATING SNOWFALL. LIKE MOST WINTER STORMS...THIS SYSTEM WILL COME IN 2 PARTS...1ST WILL BE MID LEVEL WAA AND ASSOCIATED LIFT/MOISTURE BTWN 06Z-12Z MONDAY...WITH BRIEF BREAK...BEFORE WRAP AROUND MID LEVEL MOISTURE AND DEFORMATION ZONES DEVELOPS ON BACKSIDE AFT 18Z MONDAY. STILL SOME QUESTION IF INSTABILITY CAN DEVELOP IN DRY SLOT ON MONDAY...FOR POTENTIAL STORMS. THINKING PLENTY OF LOW LEVEL MOISTURE AND CLOUDS WILL LIMIT SURFACE HEATING...ESPECIALLY WITH SURFACE LOW TRACKING TO OUR SOUTH...PLACING MOST OF OUR OUR AREA ON THE COOL SIDE OF THE STORM. HAVE NOTED THE 12Z GFS SHOWING SURFACE BASED CAPE BTWN 1500 AND 1800 J/KG ACROSS CENTRAL/EASTERN VT ON MONDAY AFTERNOON...WHICH COMBINED WITH POSITION OF POTENT 5H VORT AND AVAILABLE MOISTURE WOULD SUPPORT SOME THUNDERSTORM DEVELOPMENT. THIS POTENTIAL WILL NEED TO BE WATCHED CAREFULLY ESPECIALLY IF SURFACE LOW PRES TRACKS FURTHER WEST AND PLACES OUR OUR AREA IN THE WARM SECTOR ON MONDAY AFTERNOON...WITH GREATER INSTABILITY. A GENERAL LIGHT TO MODERATE RAIN WILL OCCUR ON MONDAY NIGHT...ASSOCIATED WITH BACK SIDE DEFORMATION. BOTH GFS/NAM SHOW GOOD RIBBON OF 850 TO 500MB RH WITH SOME ENHANCED 850 TO 700MB UVVS ACROSS THE CHAMPLAIN VALLEY AND POINTS EAST. QPF WILL RANGE FROM 0.25 TO 0.50 ACROSS THE SAINT LAWRENCE VALLEY TO 0.50 TO 1.50" ACROSS THE ADIRONDACKS INTO EASTERN VT. NO WIDESPREAD HYDRO ISSUES ARE ANTICIPATED ATTM. TEMPS WILL BE TRICKY AND HIGHLY DEPEND UPON AMOUNT OF SUNSHINE ON MONDAY...THINKING MAINLY 60S MOUNTAINS TO 70S VALLEYS WITH LOWS GENERALLY IN THE 50S TO NEAR 60F. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 318 PM EDT SATURDAY...HIGHLY AMPLIFIED PATTERN WILL PREVAIL THROUGH THE EXTENDED PORTION OF THE FORECAST WITH DEEP TROUGH OVER THE EASTERN THIRD OF THE U.S. WITH A LARGE RIDGE OVER THE WEST. CHANCES FOR RAIN WILL BE DECREASING TUESDAY MORNING AS SHORTWAVE AND ASSOCIATED WEAK SURFACE LOW DEPART INTO EASTERN CANADA. DESPITE THE PRESENCE OF LARGE UPPER TROUGH OVER THE REGION...EXPECT MUCH OF THE TIME TO BE DRY TUESDAY AFTERNOON THROUGH FRIDAY. ANY SHORTWAVES MOVING THROUGH THE MEAN TROUGH DIFFICULT TO TIME...AND WITH LACK OF MOISTURE AND LARGE SCALE FORCING...EXPECT ANY SHOWERS TO BECOME MORE DIURNALLY DRIVEN...WITH BEST CHANCE DURING THE AFTERNOON HOURS EACH DAY. HAVE GONE WITH EITHER SLIGHT CHANCE OR LOW CHANCE POPS MOST DAYS...AND MAINLY DRY FOR THE OVERNIGHT HOURS. NOT MUCH CHANGE NEXT SATURDAY...ALTHOUGH ECMWF AND GFS DIFFER BY THIS TIME IN POSITION OF UPPER TROUGH. ECMWF MORE PROGRESSIVE WHILE GFS HAS TROUGH RETROGRADING. HAVE GONE WITH 20-30 PERCENT CHANCE OF SHOWERS. BELOW NORMAL TEMPS EXPECTED THROUGH MIDWEEK. 850 MB TEMPS PROGGED TO BE NO HIGHER THAN +10C TUE THEN MODERATING SLIGHTLY TO 11-13C WED THROUGH FRI. WITH PARTIAL SUN...THIS SUPPORTS HIGHS ONLY IN THE 70S TUE/WED...MODERATING TO AROUND 80 THU/FRI...WITH LITTLE CHANGE SATURDAY. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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THROUGH 06Z MONDAY..TRENDING MVFR EARLY THIS MORNING WITH SHOWERS ALREADY OVER THE REGION AND WITH THUNDERSTORMS MOVING INTO THE REGION FROM ONTARIO ASSOCIATED WITH A WEAK WARM FRONT. CHANCE OF SHOWERS ARE NEAR 80 PERCENT THROUGH ABOUT 15Z TODAY THEN DECREASE. CHANCES OF THUNDER ARE INCREASING ESPECIALLY FROM SLK TO BTV AND RUT TO MPV MOVING WEST TO EAST 09-13Z BUT WILL HANDLE WITH AMENDMENTS AS IT REMAINS TO BE SEEN EXACTLY WHERE THE THUNDERSTORMS TRACK AND IF THEY HOLD TOGETHER. VISIBILITIES EXPECTED TO REMAIN MAINLY VFR...EXCEPT SOME BRIEF REDUCTIONS TO MVFR/IFR POSSIBLE IN ANY HEAVIER SHOWERS OR ISOLATED THUNDERSTORMS. CEILINGS WILL GRADUALLY LOWER AND PERIODS OF MVFR ARE LIKELY ON BACK SIDE OF RAIN SHOWERS...LASTING UNTIL LATE MORNING WHEN SHOWER THREAT DECREASES. CEILINGS LIFT BACK TO VFR BY SUNDAY AFTERNOON. SCATTERED SHOWER AND ISOLATED THUNDERSTORM DEVELOPMENT POSSIBLE AGAIN SUNDAY AFTERNOON/EVENING AHEAD OF A SLOW SOUTHWARD MOVING COLD FRONT IN CANADA. WILL SHOW WITH VCSH/VCTS FOR NOW AS PROBABILITIES DROP TO 20-30 PERCENT. SHOWER AND THUNDER CHANCES DROP THIS EVENING UNDER VFR CONDITIONS. COULD BE SOME FG/BR CHANCES LATER TONIGHT IF CLEARING SKIES AND LIGHT WINDS PREVAIL AS FRONTAL SYSTEM STALLS TO OUR NORTH. LIGHT SOUTH WINDS TONIGHT TURN SOUTH/SOUTHWEST ON SUNDAY FROM 5 TO 10 KNOTS. SOME GUSTS TO 20 KNOTS POSSIBLE. OUTLOOK 06Z MONDAY THROUGH THURSDAY... 06Z MON - 12Z TUE...PERIODS OF MVFR IN RAIN SHOWERS AND ISOLATED THUNDERSTORMS. LOCAL IFR POSSIBLE. 12Z TUE - 12Z THU...TRENDING VFR. POSSIBLE IFR/LOWER VISIBILITY IN OVERNIGHT FOG/MIST MPV AND SLK. 12Z THU ONWARD...MAINLY VFR ALTHOUGH BRIEF PERIODS OF MVFR POSSIBLE IN SCATTERED SHOWERS...MAINLY SLK/MSS.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...TABER NEAR TERM...EVENSON/LOCONTO SHORT TERM...TABER LONG TERM...RJS AVIATION...SISSON

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