Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 271421 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 1021 AM EDT SUN JUL 27 2014 .SYNOPSIS... ACTIVE PERIOD OF WEATHER IS EXPECTED ACROSS THE NORTH COUNTRY TODAY INTO MONDAY. INITIAL AREA OF SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE REGION THROUGH THE MORNING HOURS...WITH RE- DEVELOPMENT OF THUNDERSTORMS...SOME STRONG...DURING THE AFTERNOON. A POTENT MID-SUMMER LOW WILL TRACK ACROSS THE NORTH COUNTRY ON MONDAY WITH A WETTING RAINFALL TO THE REGION WITH POTENTIAL FOR THUNDERSTORMS ACROSS EASTERN VERMONT. GRADUALLY IMPROVING CONDITIONS TUESDAY INTO MIDWEEK...WITH HIGH TEMPERATURES BEING A FEW DEGREES BELOW NORMAL THROUGH MIDWEEK. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... AS OF 1019 AM EDT SUNDAY...CRNT RADAR SHOWING A BAND OF MODERATE RAIN WITH EMBEDDED RUMBLES OF THUNDER ACRS CENTRAL/EASTERN VT ATTM. HAVE UPDATED TO TRIM BACK POPS ACRS THE CPV/DACKS TO CHC. CONTINUED TO MENTION HIGH CAT POPS FOR PRECIP ACRS CENTRAL/EASTERN VT...BUT THIS WL CLR OUR CWA BY 16Z TODAY. RAINFALL AMOUNTS HAVE RANGED BTWN 0.10 AND 0.50 ASSOCIATED WITH THIS FEATURE...WITH 0.30 FALLING AT BTV THRU 10 AM. NEXT FCST CHALLENGE WL BE POTENTIAL FOR ADDITIONAL ACTIVITY THIS AFTN/EVENING. VIS SATL PIC SHOWS A FEW BREAKS ACRS THE SLV...WHICH WL SPREAD EAST INTO THE CPV/VT BY EARLY THIS AFTN...ASSOCIATED WITH SUBSIDENCE BEHIND S/W ENERGY. WATER VAPOR SHOWS ANOTHER WEAK 5H VORT JUST NORTH OF LAKE ONTARIO...WHICH WL PASS ALONG OUR CENTRAL/NORTHERN CWA BTWN 17Z- 22Z TODAY. THINKING THIS ENERGY ALOFT...COMBINED WITH SOME SFC HEATING WL RESULT IN WIDELY SCATTERED SHOWERS/STORMS THIS AFTN. THE LIMITED INSTABILITY AND ULVL FORCING WL KEEP POPS IN THE 30 TO 40% RANGE THIS AFTN. IF ENOUGH INSTABILITY DEVELOPS ACRS THE CPV...FROM SFC HEATING...A FEW STRONGER STORMS COULD BE POSSIBLE. LATEST HRRR AND BTV4KM HINT AT THIS POTENTIAL WITH SFC BASED CAPE VALUES AROUND 1500 J/KG AND DEEP LAYER SHEAR VALUES AROUND 30 TO 35 KNOTS. THESE SOLUTIONS SUPPORT PULSE LIKE STORMS...WITH NO REAL ORGANIZATION. TEMPS WITH CLOUDS AND PRECIP THIS MORNING WL SLOWLY CLIMB INTO THE LOWER 70S (MTNS) TO LOWER 80S (SLV/CPV) BY EARLY THIS AFTN...ESPECIALLY IF A FEW BREAKS IN THE OVERCAST CAN DEVELOP. PREVIOUS NEAR-TERM DISCUSSION ISSUED AT 437 AM EDT SUNDAY FOLLOWS... ONGOING LINE OF HEAVIER SHOWERS AND THUNDERSTORMS NOW ENTERING THE ST. LAWRENCE VALLEY EARLY THIS MORNING. THIS ACTIVITY TIED TO AN INITIAL SHORTWAVE MOVING INTO EASTERN VERMONT PER WV IMAGERY AND WEAK INSTABILITY ALOFT (SHOWALTERS -1 TO -2). LIGHTER SHOWERS ACROSS WESTERN HALF OF VERMONT. EXPECT THE SOLID LINE OF HEAVIER SHOWERS/THUNDERSTORMS 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 THROUGH THE MORNING. 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 6C/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 MID-LEVEL SUBSIDENT/WEAK HEIGHT RISE REGIME. THAT SHOULD HELP TO SUPPRESS OR KEEP A MORE ISOLATED TO WIDELY SCATTERED COVERAGE TO ANY STORMS THAT CAN DEVELOP 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 437 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. 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 MARKS AS TO THIS LOW`S EXACT TRACK ESPECIALLY IN LIGHT OF POTENTIAL MASS FIELD CHANGES GIVEN A POTENTIAL SEVERE WEATHER EVENT IN THE MID-ATLANTIC /APPALACHIANS TODAY. THERE APPEARS TO BE BETTER AGREEMENT ON A MORE INTERIOR TRACK (LOW ROUGHLY CENTERED OVER THE HUDSON VALLEY REGION BY 12Z MONDAY) - AND THERE ARE GOOD SIGNALS IN HIGH RES MODELS OF A BAND OF MODERATE RAIN ON THE NORTHWEST PERIPHERY OF SFC LOW`S TRACK. THAT BAND 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 421 AM EDT SUNDAY... A SLOW WARMING TREND TO NEAR NORMAL TEMPERATURES IS EXPECTED BY THE END OF THE WEEK WITH THE HIGHEST CHANCE OF SHOWERS AND THUNDERSTORMS ON THURSDAY. MODELS IN GOOD AGREEMENT THAT A DEEP LARGE SCALE TROUGH WILL REMAIN OVER THE EASTERN US CENTERED NEAR 80 DEG W WITH A RIDGE OVER THE INTER-MOUNTAIN WEST THROUGHOUT THE PERIOD...THOUGH WEAKENING WITH RISING HEIGHTS. THOUGH A SHOWER CAN`T BE COMPLETELY RULED OUT ANY AFTERNOON DURING THIS PERIOD WITH THE UPPER TROUGH JUST OFF TO THE WEST...THE BEST CHANCE FOR SEEING SHOWERS AND THUNDERSTORMS WILL BE THURSDAY AFTERNOON AS A SHORT WAVE WITH COLD AIR ALOFT SWINGS ACROSS THE AREA WITH SOME INSTABILITY AND SOME QG FORCING. THE UPPER TROUGH WEAKENS BUT REMAINS IN PLACE FRIDAY INTO THE WEEKEND BUT RETROGRADES A FEW DEGREES WESTWARD IN RESPONSE TO A BUILDING ATLANTIC RIDGE ALOFT, RISING HEIGHTS OVER THE EAST COAST WITH A BERMUDA HIGH STRENGTHENING AT THE SURFACE...WHICH IS FAIRLY TYPICAL FOR LATE SUMMER. SOME SMALL CHANCE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE EACH DAY AS AREA REMAINS LOCKED INTO THE EASTERN SIDE OF THE UPPER TROF. SLIGHTLY BELOW NORMAL MAX TEMPS ARE EXPECTED WEDNESDAY WITH PARTLY SUNNY SKIES. HIGHS TEMPS MAINLY IN THE 70S WITH 850 TEMPS ONLY AROUND 8-10C. 850 MB TEMPS WARM A COUPLE DEGREES EACH DAY SO THAT BY THURSDAY THROUGH SATURDAY SHOULD BE 12-14C. WITH PARTIAL SUN UNDER DIURNAL CUMULUS CLOUDS EXPECT HIGHS MODERATING TO NEAR NORMAL - UPPER 70S LOWER 80S. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... THROUGH 06Z MONDAY..MVFR LCL IFR 12-16Z THIS MORNING WITH SHOWERS AND THUNDERSTORMS AS A WEAK WARM FRONT PUSHES THROUGH THE REGION. CHANCE OF SHOWERS ARE NEAR 80 PERCENT THROUGH ABOUT 16Z TODAY THEN DECREASE. CHANCES OF THUNDER INCREASING ESPECIALLY PBG BTV RUT MPV MOVING WEST TO EAST 12-16Z. VISIBILITIES EXPECTED TO REMAIN MAINLY VFR...EXCEPT SOME BRIEF REDUCTIONS TO MVFR/IFR POSSIBLE IN ANY HEAVIER SHOWERS OR ISOLATED THUNDERSTORMS. PERIODS OF MVFR ARE LIKELY ON BACK SIDE OF RAIN SHOWERS...LASTING UNTIL LATE MORNING WHEN SHOWER THREAT DECREASES. CEILINGS LIFT BACK TO VFR THIS AFTERNOON. ISOLATED THUNDERSTORM DEVELOPMENT POSSIBLE AGAIN THIS AFTERNOON/EVENING AHEAD OF A SLOW SOUTHWARD MOVING COLD FRONT IN CANADA BUT POBABILITIES ONLY 20-30 PERCENT SO HAVE LEFT OUT ALL BUT SLK WHERE TERRAIN MAY HELP. 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 WHEN 09-12Z MORE SHOWERS AND POSSIBLE THUNDER RETURN ALONG WITH A MVFR/IFR. SOUTH/SOUTHWEST WINDS 5 TO 10 KNOTS TODAY. SOME GUSTS TO 20 KNOTS POSSIBLE. OUTLOOK 12Z MONDAY THROUGH THURSDAY... 12Z MON - 12Z TUE...PERIODS OF MVFR IN RAIN AND ISOLATED THUNDERSTORMS. LOCAL IFR POSSIBLE IN HEAVIER RAIN. 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. && .MARINE... AS OF 550 AM EDT SUNDAY...A LAKE THUNDERSTORM ADVISORY IS NOW IN EFFECT FOR LAKE CHAMPLAIN. A LINE OF THUNDERSTORMS HAS DEVELOPED OVERNIGHT AND NOW EXTENDS FROM ST. LAWRENCE COUNTY TO THE EASTERN SHORE OF LAKE ONTARIO. WHILE THERE IS NO IMMEDIATE THREAT OF LIGHTNING ON LAKE CHAMPLAIN...EXPECT THESE STORMS TO APPROACH LAKE CHAMPLAIN BY MID-MORNING. BOATERS AND OTHERS NEAR THE LAKE SHOULD BE PREPARED TO SEEK SAFE HARBOR AS THESE STORMS MOVE THROUGH...WITH OCCASIONAL TO FREQUENT LIGHTNING...HEAVY DOWNPOURS PRODUCING BRIEFLY LOWERED VISIBILITY...AND ROUGH SEAS. ADDITIONAL THUNDERSTORMS MAY DEVELOP AGAIN LATER THIS AFTERNOON. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...LOCONTO NEAR TERM...TABER/LOCONTO SHORT TERM...LOCONTO LONG TERM...SISSON AVIATION...SISSON MARINE...LOCONTO

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