Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 270816 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 416 AM EDT SUN JUL 27 2014 .SYNOPSIS... ACTIVE PERIOD OF WEATHER EXPECTED TODAY INTO MONDAY. INITIAL SHOWERS AND THUNDERSTORMS TO MOVE ACROSS THE NORTH COUNTRY THIS MORNING...WITH RE-DEVELOPING ISOLATED STORMS BECOMING STRONG LATER THIS AFTERNOON. A STRONG MID-SUMMER LOW PRESSURE AREA THEN MOVES ACROSS THE NORTH COUNTRY MONDAY...SPREADING A WETTING RAIN ACROSS MOST OF THE REGION WITH THUNDERSTORMS FOR EASTERN VERMONT. MORE GRADUAL IMPROVEMENT TUESDAY INTO MIDWEEK WITH HIGH TEMPERATURES SLIGHTLY BELOW NORMAL. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... AS OF 416 AM EDT SUNDAY...ONGOING SHOWERS TAKE PLACE EARLY THIS ACROSS WESTERN HALF OF VERMONT...BUT A LINE OF HEAVIER SHOWERS AND THUNDERSTORMS NOW APPROACHING INTO EARLY THIS MORNING. THIS ACTIVITY TIED TO AN INITIAL SHORTWAVE MOVING INTO EASTERN ONTARIO PER WV IMAGERY AND WEAK INSTABILITY ALOFT (SHOWALTERS OF -1 TO -2). EXPECT THESE SHOWERS AND STORMS TO MOVE ACROSS THE GREENS AND INTO EASTERN VERMONT THROUGH THE MORNING/EARLY AFTN HOURS. I`VE SHOWN RELATIVELY HIGH POP (LIKELY TO LOW CATEGORICAL) TO COVER THIS ONGOING ACTIVITY. FOCUS FOR THE AFTN THEN SHIFTS TOWARDS POTENTIAL FOR RE-DEVELOPING CONVECTION AND ITS AREAL COVERAGE. FEEL THAT SOME CLEARING IN THE WAKE OF MORNING SHOWERS WILL ALLOW FOR SOME DESTABILIZATION. I DON`T THINK THE DEGREE OF INSTABILITY WILL BE QUITE AS HIGH AS WHAT THE 4-KM NAM OR WRF BTV-4 IS SHOWING (NEAR 2000 J/KG CAPE)...BUT VALUES AROUND HALF THAT SEEM REASONABLE WITH BREAKS IN THE CLOUDS AND MID-LEVEL LAPSE RATES OF AROUND 6 C/KM. WIND FIELDS ALSO STRENGTHEN TO PRODUCE 0-6 KM BULK SHEAR MAGNITUDES OF 30-35 KTS. HOWEVER BY AFTN THE NORTH COUNTRY WILL BE IN BETWEEN THE DEPARTING SHORTWAVE AND A MORE POTENT SHORTWAVE TROUGH DIVING SOUTHWARD TOWARD THE CENTRAL APPALACHIANS...IN A MID-LEVEL SUBSIDENT/WEAK HEIGHT RISE REGIME. THAT SHOULD HELP TO SUPPRESS OR KEEP A MORE ISOLATED TO WIDELY SCATTERED COVERAGE TO STORMS LATER THIS AFTERNOON. I THOUGHT ABOUT INTRODUCING ENHANCED WORDING FOR GUSTY WINDS AND SMALL HAIL BUT OVERALL LIMITED AREAL COVERAGE SUGGESTED AGAINST DOING SO. IT`S ALSO DIFFICULT TO PINPOINT A FAVORED AREA FOR STRONGER STORMS TODAY...BUT WOULD THINK EASTERN VERMONT WOULD HAVE A TOUGHER TIME CLEARING AND LOWER INSTABILITY THERE. I WILL MENTION POTENTIAL FOR STRONGER STORMS IN THE HWO HOWEVER. OVERALL QPF TODAY GENERALLY A QUARTER TO AS MUCH AS A HALF-INCH (LOCALLY HIGHER IN THUNDERSTORM DOWNPOURS). HIGHS SHOULD TOP OUT IN THE 70S TO A SPOT 80 TODAY...GENERALLY COOLEST ACROSS THE HIGH TERRAIN AND IN EASTERN VERMONT WHERE SHOWERS/STORMS WILL TAKE LONGER TO CLEAR (I.E. LESS TIME FOR AFTN BREAKS IN CLOUDS). && .SHORT TERM /7 PM THIS EVENING THROUGH TUESDAY/... AS OF 416 AM EDT SUNDAY...ACTIVE PERIOD OF WEATHER THEN CONTINUES LATER SUNDAY NIGHT AND ESPECIALLY ON MONDAY. MORE GRADUAL IMPROVEMENT FOR TUESDAY BUT STILL GENERALLY UNSETTLED WITH THE NORTH COUNTRY UNDER A WELL-ADVERTISED 500 MB TROUGH ALOFT. TONIGHT: STILL CAN`T RULE OUT AN ISOLATED STRONGER STORM EARLY EVENING BUT ALREADY LIMITED INSTABILITY WILL BECOME EVEN MORE SO BY DARK. THE STRONG...POSITIVELY TILTED SHORTWAVE TROUGH ASSUMES A NEGATIVE TILT BY 12Z MONDAY AND INDUCES SFC LOW DEVELOPMENT NEAR CENTRAL PA LATER TONIGHT. THERE`S SOME QUESTION AS TO THIS LOW`S EXACT TRACK CONSIDERING POTENTIAL MASS FIELD CHANGES IN GUIDANCE GIVEN A POTENTIAL SEVERE WEATHER EVENT IN THE MID- ATLANTIC/APPALACHIANS TODAY. THAT SAID THERE`S BETTER AGREEMENT ON A MORE INTERIOR TRACK WITH 00Z GUIDANCE SUITE (LOW ROUGHLY CENTERED OVER THE HUDSON VALLEY REGION BY 12Z MONDAY). THERE ARE GOOD SIGNALS IN HIGH RES MODELS OF A BAND OF MODERATE RAIN ON THE NORTHWEST PERIPHERY OF SFC LOW`S TRACK. LEADING EDGE OF MODERATE RAIN LOOKS TO OVERSPREAD SOUTHERN VERMONT INTO THE ADIRONDACKS THROUGH 12Z MONDAY. INITIALLY KEPT POPS AROUND CHANCE CATEGORY BUT BEGIN TO TREND UPWARD AFTER MIDNIGHT TO LIKELY/LOW CATEGORICAL BY THE PRE- DAWN HOURS. LOWS UNLIKELY TO FALL MUCH UNDER OVERCAST SKIES...UPPER 50S TO MID 60S GENERALLY A DEGREE OR TWO WARMER THAN MAV OR MET MOS GUIDANCE. MONDAY & MONDAY NIGHT: SFC LOW THEN TRACKS UP THE CHAMPLAIN VALLEY/GREEN MOUNTAINS THROUGH 00Z TUESDAY...500 MB TROUGH ALSO PIVOTS NORTHWARD BUT APPEARS TO CLOSE OFF BY MONDAY EVENING. WITH THAT EXPECTED LOW TRACK...IT LEAVES CENTRAL/EASTERN VERMONT IN THE WARM SECTOR. FAVORABLE WIND SHEAR PARAMETERS FOR STRONG THUNDERSTORMS IF GREATER INSTABILITY CAN BE REALIZED (GENERALLY IS HIGHEST IN THE 00Z GFS) IN THIS CORRIDOR. NORTHWEST OF THE LOW TRACK...MORE STRATIFORM MODERATE RAIN WILL PIVOT NORTH-NORTHEASTWARD ACROSS NORTHERN NY AND THE NORTHERN CHAMPLAIN VALLEY. I`VE INDICATED CHANCE THUNDER FOR CENTRAL AND EASTERN VERMONT IN PROGGED WARM SECTOR...BUT HAVE OTHERWISE KEPT THUNDER OUT ELSEWHERE WHERE IT`S LIKELY TO BE MORE RAIN-COOLED/STABLE. CATEGORICAL POPS OFFERED MONDAY WITH GRADUAL TAPER TO HIGH CHANCE/LIKELY THROUGH MONDAY EVENING. TEMPS ARE TRICKY/DEPENDENT ON LOW TRACK...BUT LIKELY TO BE BELOW NORMAL AND CLOSER TO NORMAL IF WARM SECTOR CAN GET ESTABLISHED. HIGHS IN NORTHERN NY MAY STRUGGLE TO REACH 70 DEGREES IN A CLOUDY/RAINY DAY...AND CLOSER TO THE MID/UPPER 70S IN CENTRAL AND EASTERN VERMONT. QPF MONDAY RANGES FROM LESS THAN A HALF-INCH FOR THE SAINT LAWRENCE VALLEY... .75-1" FOR MUCH OF VERMONT TO JUST A TICK OVER AN INCH FOR THE ADIRONDACKS. NOT ANTICIPATING ANY HYDRO ISSUES FROM THIS AMOUNT OF RAIN GIVEN HOW DRY IT HAS BEEN. TUESDAY: UPPER TROUGH EXITS WITH STILL SOME LINGERING SHOWERS PARTICULARLY ACROSS HIGHER TERRAIN. NORTHWEST FLOW...MDT COLD ADVECTION (850 TEMPS DURING TUESDAY PLUNGE TO +6 TO +8C) AND PARTLY CLOUDY SKIES PRODUCES BELOW NORMAL HIGHS IN THE 60S TO THE LOWER 70S. && .LONG TERM /TUESDAY NIGHT 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 /08Z SUNDAY THROUGH THURSDAY/... 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. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...LOCONTO NEAR TERM...LOCONTO SHORT TERM...LOCONTO LONG TERM...RJS AVIATION...SISSON

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