Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 261146 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 746 AM EDT SAT JUL 26 2014 .SYNOPSIS... THOUGH TODAY WILL START OFF DRY...INCREASING CLOUDS ARE EXPECTED LATE IN THE DAY. SHOWERS AND THUNDERSTORMS ARE EXPECTED TONIGHT INTO PARTS OF SUNDAY AS A WARM FRONT INTERACTS WITH A WEAK UPPER- LEVEL DISTURBANCE. A STRONGER STORM SYSTEM WILL BRING WITH IT A RENEWED THREAT OF RAIN AND THUNDERSTORMS FOR MONDAY INTO TUESDAY. SLIGHTLY BELOW NORMAL TEMPS EXPECTED FOR EARLY NEXT WEEK...TRENDING BACK TOWARD SEASONAL NORMALS BY MIDWEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AS OF 712 AM EDT SATURDAY...I OPTED TO ADJUST POPS A BIT TO BRING A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS INTO THE ST. LAWRENCE VALLEY BY AFTERNOON. REGIONAL RADAR SHOWS SOME LIGHT ECHO RETURNS NEAR THE NORTHERN SHORES OF LAKE ONTARIO. THESE LIGHT SHOWERS FORMING ON ILL-DEFINED WARM FRONT (REALLY ONLY EVIDENT IN 1000-500 MB THICKNESS FIELDS) BY A WEAK 500 MB VORT MAX. SHOWERS THEMSELVES MOVING MORE EAST-SOUTHEAST THAN EAST...SO MAY TAKE ITS TIME GETTING INTO THE ST. LAWRENCE VALLEY. HOWEVER THE VORT MAX EXPECTED TO TRIGGER SHOWERS AND POSSIBLE STORMS TONIGHT STILL IS BACK ACROSS THE GREAT LAKES WITH A GREATER OVERALL COVERAGE ANTICIPATED LATER THIS EVENING. ASIDE FROM THAT CHANGE...ONLY OTHER ADJUSTMENT WAS TO MATCH CURRENT OBS. PREVIOUS NEAR-TERM DISCUSSION ISSUED AT 435 AM EDT SATURDAY FOLLOWS... WEST TO WEST-NORTHWEST FLOW PREVAILS AT MID TO UPPER LEVELS ACROSS THE NORTH COUNTRY...BETWEEN NEARLY STATIONARY CYCLONIC GYRE OVER NORTHERN QUEBEC AND LARGE HEAT RIDGE CENTERED OVER THE SOUTHERN PLAINS STATES. HIGH CLOUDS THIS MORNING PRECEDE A WEAK WARM FRONT ROUGHLY LOCATED EARLY THIS MORNING ACROSS SOUTHERN NEW YORK AND INTO THE GREAT LAKES. THAT FRONTAL ZONE WILL SLOWLY CREEP ITS WAY NORTHEASTWARD TOWARDS THE NORTH COUNTRY LATER TODAY INTO TONIGHT. THOUGH THE MORNING HOURS WILL START OFF WITH AT LEAST FILTERED SUN THROUGH THE HIGH CLOUDS...ANTICIPATE CLOUDS TO INCREASE FURTHER FROM WEST TO EAST BY LATE AFTERNOON/EARLY EVENING. 850 TEMPS OF +12C TODAY COMBINED WITH PARTIAL SUNSHINE SHOULD ALLOW HIGHS TO TOP OUT IN THE 70S WITH LOWER 80S IN THE CHAMPLAIN VALLEY AND SOUTHERN VERMONT. SOUTHWEST WINDS AROUD 10 MPH TODAY. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/... AS OF 435 AM EDT SATURDAY...THE PATTERN THEN TURNS MORE ACTIVE LATER TONIGHT/MOST OF SUNDAY AND ESPECIALLY GOING INTO MONDAY. FOR TONIGHT: A WEAK VORTICITY MAX EMBEDDED IN WEST FLOW ALOFT INTERACTS WITH APPROACHING WARM FRONT...SPAWNING AREAS OF SHOWERS. MID-LEVEL LAPSE RATES DO STEEPEN SOME LATE TO AROUND 6C/KM TOWARD MORNING...AND SLIGHTLY NEGATIVE SHOWALTER INDICES OF -1 TO -2 PER 00Z NAM/WRF AND GFS LEAVES OPEN THE POSSIBILITY OF THUNDER THOUGH NOT EXPECTING ANYTHING SIGNIFICANT. I USED NAM/SREF 3-HRLY POP AND ADJUSTED BASED ON HI-RES GUIDANCE...WITH LIKELY POPS (CHANCE THUNDER) ANTICIPATED AROUND AND AFTER MIDNIGHT. OVERCAST SKIES SHOULD KEEP LOWS IN THE 60S (COOLER MID-UPPER 50S IN THE TYPICALLY COOLER NORTHEAST KINGDOM AND ADIRONDACKS). SUNDAY: STILL EXPECT THERE TO BE SHOWERS/THUNDER ONGOING PRIMARILY ACROSS THE EASTERN HALF OF THE CWA. A GENERAL DECREASE IN POPS IS FORECAST AS WEAK 500-MB SHORTWAVE EXITS INTO EASTERN QUEBEC...BUT STILL HAVE CARRIED AT LEAST CHANCE POPS INTO SUNDAY EVENING. SPC`S DAY2 OUTLOOK PARTS OF RUTLAND AND WINDSOR COUNTIES IN A SLIGHT RISK AREA. THERE`S LARGE VARIATION IN FORECAST CAPE VALUES BETWEEN NAM/WRF AND GFS ACROSS CENTRAL AND SOUTHERN VERMONT (AS HIGH AS 1500 J/KG AT VSF PER THE GFS). THOUGH I`VE INCLUDED CHANCE THUNDER SUNDAY...I DON`T THINK ACTUAL CAPE VALUES WILL GET THAT HIGH AS THERE SHOULD BE PLENTY OF CLOUDS AROUND TO LIMIT BETTER SFC HEATING. WIND FIELDS INCREASE SOME. UNDER PARTLY TO MOSTLY CLOUDY SKIES LOOKING AT HIGHS ONLY IN THE 70S. SUNDAY NIGHT: IF THERE`S A BREAK IN THE UNSETTLED WEATHER (ALBEIT BRIEF) IT WILL BE ON SUNDAY NIGHT. THE NORTH COUNTRY WILL BE UNDER WEAK 500 MB HEIGHT RISES EARLY SUNDAY NIGHT AHEAD OF A RATHER STRONG SHORTWAVE TROUGH EXPECTED TO BE NEAR THE SOUTHERN GREAT LAKES. STARTED TO INCREASE POPS AFTER MIDNIGHT TO HIGH CHANCE/LIKELY AHEAD OF MORE SIGNIFICANT SYSTEM. LOWS GENERALLY MID 50S TO LOW 60S. MONDAY: A POTENT SHORTWAVE TROUGH (NOW ACROSS THE CANADIAN PRAIRIES) WILL BECOME NEGATIVELY TILTED DURING THIS PERIOD - INDUCING A SFC LOW TO DEVELOP EARLY MONDAY OVER INTERIOR CENTRAL/SOUTHERN NEW ENGLAND. NEARLY ALL GUIDANCE SHOW A GOOD AMOUNT OF PRECIPITATION ESPECIALLY FOR EASTERN VERMONT MONDAY...FOCUSED SOMEWHAT ON A MID-LEVEL DEFORMATION ZONE. A BIGGER QUESTION IS THE TRACK OF THE SFC LOW AND WHERE/IF THE WARM SECTOR CAN GET ESTABLISHED SOMEWHERE ACROSS THE NORTH COUNTRY. THE NAM IS FURTHEST EAST WITH PROGGED LOW TRACK...WHILE THE GFS TAKES A MORE INLAND TRACK INTO CENTRAL NEW ENGLAND. IF THE GFS WERE CORRECT...COULD SEE POTENTIAL FOR STRONG THUNDERSTORMS FOR EASTERN VERMONT GIVEN STRONG SYNOPTIC FORCING...0-6KM SHEAR VALUES OF 35-45 KTS AND CAPES OF 1000-1500 J/KG. IT`S SOMETHING THAT WILL BEAR CLOSE WATCH. HIGH LIKELY POPS ACROSS EASTERN VT TAPER TO CHANCE ACROSS THE ST. LAWRENCE VALLEY FOR RAIN/CHANCE THUNDER. QPF FROM 06Z - 18Z MONDAY RUNS FROM .25" ST. LAWRENCE VALLEY TO .75"-1" FOR SOUTHERN AND EASTERN VT. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AS OF 435 AM EDT SATURDAY...COOLER THAN NORMAL AND WET WEATHER IS EXPECTED EARLY TUESDAY THEN IMPROVING THE REST OF THE WEEK. A SLOW WARMING TREND TO NEAR NORMAL TEMPERATURES IS EXPECTED BY THE END OF THE WEEK WITH ONLY SLIGHT CHANCES OF SHOWERS. 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 INTERMOUNTAIN WEST THROUGHOUT THE PERIOD...THOUGH WEAKENING WITH RISING HEIGHTS WED - FRI. THE BEST CHANCE FOR SEEING WIDESPREAD RAIN WILL BE MONDAY NIGHT INTO EARLY TUESDAY. RAIN WILL BE FORCED BY BLOCKED COOL MOIST NORTH TO NORTHWEST CYCLONIC UPSLOPE FLOW RIGHT UNDER THE TROUGH ALOFT AND BEHIND DEPARTING LOW PRESSURE IN EASTERN CANADA. GFS FROUDE NUMBERS ARE VERY LOW (0.10) SUGGESTING THAT PRECIP MAY BE ENHANCED FROM THE GREEN MOUNTAINS WESTWARD ALL THE WAY BTV IN THE CHAMPLAIN VALLEY WITH GENERAL LIGHTER RAINS ELSEWHERE. EXPECTING PRECIP CHANCES TO DROP OFF LATER TUESDAY AS THE LOW MOVES AWAY. THE UPPER TROUGH WEAKENS BUT REMAINS IN PLACE WEDNESDAY THROUGH FRIDAY. WITH AFTERNOON INSTABILITY FROM RELATIVELY COOL TEMPERATURES ALOFT...THERE ARE SLIGHT CHANCES FOR SHOWERS EACH DAY MAINLY DURING THE AFTERNOON HOURS. 5 TO 10 DEGREE BELOW NORMAL MAX TEMPS ARE EXPECTED TUESDAY WITH CLOUDS AND SHOWERS. HIGHS TEMPS WILL ONLY REACH THE UPPER 60S TO LOWER 70S WITH 850 TEMPS ONLY AROUND +7C. 850 MB TEMPS WARM A COUPLE DEGREES EACH DAY SO THAT BY FRIDAY SHOULD BE 12-13C. WITH PARTIAL SUN UNDER DIURNAL CUMULUS CLOUDS EXPECT HIGHS ONLY IN THE 70S WED BUT MODERATING TO NEAR NORMAL - UPPER 70S LOWER 80S - BY THURSDAY AND FRIDAY. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... THROUGH 12Z SUNDAY...MAINLY VFR EXPECTED UNDER WEST TO SOUTHWEST SURFACE FLOW THROUGH 06Z. INTRODUCED MVFR IN -SHRA AFTER 06Z AS A WEAK WARM FRONT APPROACHES. LOOKING AT SCT CUMULUS CLOUDS AND SCT-BKN MID TO HIGH LEVEL CLOUDS THROUGH THIS EVENING. WINDS SWLY AROUND 10 KTS. A WEAK FRONTAL SYSTEM WILL BRING INCREASING AND LOWERING CLOUD CEILINGS AND A THREAT OF SHOWERS PERHAPS A THUNDERSTORM 06-12Z SUN. OUTLOOK 12Z SUNDAY THROUGH WEDNESDAY... 12Z SUN - 12Z MON...MOSTLY VFR. BRIEF PERIODS MVFR VISIBILITY IN SCT SHOWERS/STORMS. 12Z MON - 00Z WED...PERIODS OF MVFR IN SHOWERS. 00Z WED ONWARD...TRENDING VFR. POSSIBLE IFR/LOWER VISIBILITY IN OVERNIGHT FOG/MIST MPV AND SLK. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...LOCONTO NEAR TERM...LOCONTO SHORT TERM...LOCONTO LONG TERM...SISSON AVIATION...SISSON

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