Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 301148 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 748 AM EDT SAT MAY 30 2015 .SYNOPSIS... A SLOW MOVING COLD FRONT WILL PRODUCE OCCASIONAL SHOWERS AND THUNDERSTORMS THIS AFTERNOON ACROSS THE NORTH COUNTRY. LOCALIZED HEAVY DOWN POURS...FREQUENT LIGHTNING...AND GUSTY WINDS WILL BE POSSIBLE WITH ANY THUNDERSTORMS. A WIDESPREAD RAINFALL IS EXPECTED TONIGHT INTO SUNDAY...WITH ADDITIONAL SHOWERS ON MONDAY. TEMPERATURES WILL WARM BACK INTO THE 70S AND 80S TODAY...WITH BREEZY SOUTH WINDS...BUT A COOLER AND WETTER PATTERN DEVELOPS FOR SUNDAY INTO EARLY THIS UPCOMING WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AS OF 718 AM EDT SATURDAY...UPDATED FCST TO INCREASE POPS TO NEAR 100% LATE THIS AFTN INTO THIS EVENING ACROSS MOST OF THE CWA. ALSO, INCREASED WINDS ESPECIALLY IN THE CHAMPLAIN VALLEY WHERE WE ARE ALREADY GUSTING TO 29 KNOTS. CRNT THINKING IS SHORT WAVE ENERGY ENTERING WESTERN PA/NY ON WATER VAPOR WILL ENHANCE SHOWER/THUNDERSTORM DEVELOPMENT OVER NORTHERN NY AROUND 18Z THIS AFTN. THESE SHOWERS/STORMS WILL EXPAND FROM SW TO NE IN AREAL COVERAGE AND BE LOCATED ACROSS THE CHAMPLAIN VALLEY AND PARTS OF CENTRAL/NORTHERN VT BY 21Z...WITH ADDITIONAL STORMS ENTERING THE SAINT LAWRENCE VALLEY ASSOCIATED WITH THE ACTUAL SFC COLD FRONT. AMOUNT OF CLRING AND SFC HEATING/INSTABILITY WILL DETERMINE OVERALL MAGNITUDE OF STORMS...BUT THINKING CAPE VALUES BTWN 1000 AND 1500 J/KG WILL SUPPORT A FEW STRONGER STORMS WITH AN LOCALIZED SVR WIND GUSTS POSSIBLE. THE MAIN SVR THREAT WILL BE BTWN 18Z- 21Z..AS DEBRIS CLOUDS WILL STABILIZE ATMOSPHERE BY SUNSET TONIGHT. THUNDERSTORMS WILL TRANSITION INTO WIDESPREAD SHOWERS WITH EMBEDDED DOWNPOURS THIS EVENING...WITH SOME LOCALIZED HIGHER RAINFALL RATES. THE HIGHER RAINFALL RATES WILL HAVE TO BE WATCHED CLOSELY FOR ISOLATED HYDRO RELATED PROBLEMS. ALL COVERED IN CRNT FCST WITH HEAVY RAINFALL POSSIBLE. FORECAST CHALLENGE WILL BE AREAL COVERAGE OF SHOWERS AND THUNDERSTORMS ALONG WITH POTENTIAL FOR STRONGER STORMS. WATER VAPOR SHOWS A BOARD SOUTHWEST FLW ALOFT WITH PLENTY OF DEEP LAYER MOISTURE ADVECTING INTO OUR REGION...AHEAD OF A SFC COLD FRNT. THIS MOISTURE WILL PRODUCE SOME MID LEVEL CLOUDS TODAY ACROSS OUR CWA...WHICH WILL LIMIT SFC HEATING/INSTABILITY AS LATEST GUIDANCE HAS BACK OFF ON CAPE/INSTABILITY PARAMETERS ACROSS OUR CWA. RAP13/NAM 12 AND GFS SHOW CAPE VALUES BTWN 1000 AND 1500 J/KG...WITH LI`S BTWN -2C AND -4C. SREF GUIDANCE SHOWS CALIBRATED SEVERE CHANCES OF 5 TO 10%...WHILE PROBABILITY OF THUNDERSTORMS FOR TODAY IS BTWN 50 AND 60%. MEANWHILE...LLVL GRADIENT WILL INCREASE THIS AFTN...WITH ENHANCED CHANNELING OF WINDS UP THE CHAMPLAIN AND SAINT LAWRENCE RIVER VALLEYS...HELPING TO PRODUCE 0 TO 3 KM SHEAR PARAMETERS BTWN 20 AND 30 KNOTS. THE BEST DEEP LAYER SHEAR ASSOCIATED WITH MID LEVEL WINDS OF 40 TO 50 KNOTS IS LOCATED WITH MID/UPPER LVL TROF ACRS THE NORTHERN GREAT LAKES/SOUTHERN CANADA THRU THIS AFTN. ITS EXTREMELY DIFFICULT TO DETERMINE STRENGTH OF STORMS THIS AFTN...GIVEN MODEST INSTABILITY AND SHEAR PARAMETERS...BUT THINKING MAINLY A FEW STRONG STORMS...WITH MAYBE AN ISOLATED SEVERE STORM OR TWO. THINKING WINDS IN WEAK BOW LIKE LINE SEGMENTS WOULD BE THE CONVECTIVE MODE. INGREDIENTS ARE NOT LINING UP FOR A MAJOR OR WIDESPREAD OUTBREAK...AS BEST DYNAMICS AND SFC CONVERGENCE WITH FRONT ARRIVES AFT 00Z TONIGHT...WHEN INSTABILITY IS LIMITED. HOWEVER...THIS SCENARIO DOES SUPPORT SEVERAL ROUNDS OF SHOWERS WITH EMBEDDED THUNDERSTORMS AND GIVEN PWS BTWN 1.50 AND 2.0...LOCALIZED HEAVY RAINFALL IS POSSIBLE WITH ANY STORM. THINKING WIDESPREAD RAINFALL OF 0.50 TO 1.50 WITH LOCALIZED AMOUNTS NEAR 3.0" POSSIBLE. SOME MINOR POOR DRAINAGE/URBAN FLOODING IS POSSIBLE ASSOCIATED WITH THE HIGHER RAINFALL RATES...BUT GIVEN HOW DRY ITS BEEN ALL THE MAIN STEM RIVERS WILL BE ABLE TO HANDLE THE RAINFALL. PROGGED 85H TEMPS AROUND 15C SUPPORT HIGHS U70S MTNS TO MID 80S VALLEYS. BREEZY SOUTH TO SOUTHWEST WINDS OF 15 TO 25 MPH CAN BE EXPECTED WITH SOME LOCALIZED HIGHER GUSTS. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/... AS OF 330 AM EDT SATURDAY...SHOWERS AND ISOLATED THUNDERSTORMS WILL QUICKLY DECREASE IN AREAL COVERAGE AND INTENSITY AFT 04Z...WITH MAINLY LIGHT STRATO FORM RAIN LIKELY. SFC BOUNDARY IS EXPECTED TO BECOME STATIONARY ALONG THE MID ATLANTIC STATES/SOUTHERN NEW ENGLAND ON SUNDAY...WHILE ADDITIONAL ENERGY/MOISTURE NOW OVER THE MS RIVER VALLEY STREAMS INTO OUR REGION. THIS POTENT S/W ENERGY AND ASSOCIATED MID/UPPER LVL TROF WILL HELP TO DEVELOP SFC LOW PRES...WHICH WILL TRAVEL ALONG THE BOUNDARY AND ENHANCE RAINFALL ACRS OUR REGION ON SUNDAY AFTN INTO MONDAY. BOTH GFS/NAM SHOW IMPRESSIVE NOSE OF 85H JET OF 40 TO 50 KNOTS LIFTING ACRS CENTRAL NY ON SUNDAY EVENING...ALONG WITH GOOD DEEP LAYER THETA E ADVECTION...AND RRQ OF 25H JET. THIS MOISTURE AND STRONG LIFT WILL PRODUCE ANOTHER ROUND OF MODERATE TO HEAVY RAINFALL. GIVEN THE LACK OF INSTABILITY PER SOUNDINGS...AS WE ARE ON THE COLD SIDE OF FRONT...WITH JUST SOME WEAK ELEVATED INSTABILITY...NOT EXPECTING EXTREME RAINFALL RATES. HOWEVER...IF BOUNDARY LIFTS FURTHER NORTH THAN EXPECTED...SOME HIGHER PREICP RATES WILL BE POSSIBLE. GIVEN THE AVAILABLE MOISTURE AND EXPECTED LIFT...ANOTHER WIDESPREAD 1 TO 2 INCHES OF RAINFALL IS POSSIBLE SUNDAY NIGHT INTO MONDAY. THIS WILL CAUSE SOME ADDITIONAL RISES ON LOCAL STREAMS AND RIVERS...BUT ONCE AGAIN NOT EXPECTING ANY LARGE STEM RIVER FLOODING. TEMPS WILL BE BELOW NORMAL ON SUNDAY AND MONDAY WITH HIGHS GENERALLY IN THE 50S/60S AND LOWS IN THE 40S TO MID 50S. GIVEN CLOUDS AND PRECIP...AND NORTH WINDS THE DIURNAL CHANGE WILL BE LIMITED. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AS OF 415 AM EDT SATURDAY...RAIN THREAT CONTINUES MONDAY NIGHT INTO TUESDAY. WEAK SURFACE LOW PASSING JUST SOUTH OF NEW ENGLAND... WITH TROUGH EXTENDING NORTH OF THE LOW INTO FORECAST AREA. MEANWHILE...RATHER VIGOROUS UPPER LOW WILL BE TRACKING FROM GREAT LAKES MONDAY NIGHT INTO FORECAST AREA DURING TUESDAY. CHANCES FOR RAINFALL EXPECTED TO BE HIGHEST OVER VERMONT...WHERE SOME ADDITIONAL HEAVY RAINFALL POSSIBLE. THIS IS ESPECIALLY TRUE IF ECMWF IS CORRECT...WHICH IS SLOWER WITH EASTWARD SHIFT OF THE SURFACE FEATURE AND THE HIGHER PRECIPITABLE WATER VALUES. IT WILL REMAIN COOL ON TUESDAY WITH THE WET WEATHER AND CLOUDS...WITH HIGHS IN THE UPPER 50S TO MID 60S. UPPER LOW MAKES ITS WAY EAST ACROSS THE REGION TUESDAY NIGHT AND THEN HEADS INTO EASTERN CANADA WEDNESDAY. CHANCE OF SHOWERS CONTINUES TUESDAY NIGHT...BUT DRIER CONDITIONS RETURN FOR WEDNESDAY AS HEIGHTS RISE WITH DEPARTURE OF UPPER LOW WHILE SURFACE HIGH PRESSURE BUILDS INTO THE REGION. LARGE AREA OF HIGH PRESSURE THEN EXPECTED TO PREVAIL FOR THURSDAY AND FRIDAY. AIRMASS WARMING WITH TIME...SO LOOK FOR TEMPERATURES TO RETURN TO ABOVE NORMAL READINGS LATER IN THE WEEK WITH HIGHS IN THE UPPER 70S AND LOWER 80S. NIGHTTIME LOWS WILL RANGE MOSTLY FROM THE MID 40S TO MID 50S. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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THROUGH 12Z SUNDAY...VFR FOR MUCH OF TODAY WITH CONDITIONS TRENDING MVFR LATER TODAY INTO TONIGHT ALONG WITH INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS. OTHER AVIATION CONCERN WILL BE GUSTY SOUTHERLY WINDS TODAY. BROKEN MID DECK OF CLOUDS ACROSS THE FORECAST AREA EARLY THIS MORNING. EXPECT INCREASING CLOUDS TODAY WITH GRADUALLY LOWERING CEILINGS IN ADVANCE OF A COLD FRONT. STRENGTHENING GRADIENT AHEAD OF THE FRONT WILL ALLOW FOR SOUTHERLY WINDS TO INCREASE INTO THE 12-18 KT RANGE WITH GUSTS 25-30 KTS. SHOWER/THUNDERSTORM COVERAGE WILL INCREASE AFTER 18Z ACROSS NORTHERN NEW YORK AND AFTER 21Z ACROSS VERMONT. SOME STORMS COULD TURN STRONG WITH GUSTY OUTFLOW WINDS...LIGHTNING AND REDUCED VISIBILITY IN HEAVY DOWNPOURS. HAVE INDICATED SHOWERS WITH ABOUT A 4 HOUR PERIOD WITH THE A MENTION OF VCTS. OUTLOOK 12Z SUNDAY THROUGH WEDNESDAY... PERIODS OF RAIN WITH MVFR CONDITIONS SUNDAY INTO TUESDAY WITH STALLED FRONT SOUTH OF THE AREA. IMPROVING WEATHER TUESDAY NIGHT INTO WEDNESDAY WITH VFR CONDITIONS EXPECTED.
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&& .MARINE...
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AS OF 700 AM EDT SATURDAY...A LAKE WIND ADVISORY IS IN EFFECT. SOUTH WINDS WILL BE INCREASING TO 15 TO 25 KTS THIS MORNING...AND MAY REACH 30 KTS ON THE BROAD LAKE THIS AFTERNOON INTO THE EVENING HOURS. THIS DUE TO TIGHTENING PRESSURE GRADIENT IN ADVANCE OF APPROACHING COLD FRONT. WITH PASSAGE OF THE FRONT TONIGHT...WINDS WILL SHIFT INTO THE WEST AND DIMINISH A BIT TO 15 TO 20 KTS. WAVE HEIGHTS WILL BUILD TO 2 TO 4 FEET THIS AFTERNOON. THE THREAT OF SHOWERS AND THUNDERSTORMS WILL BE INCREASING THIS AFTERNOON AND EVENING AS WELL...WITH SHIFTING WINDS...HEAVY DOWNPOURS AND DANGEROUS LIGHTNING POSSIBLE IN ANY THUNDERSTORMS.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...TABER NEAR TERM...TABER SHORT TERM...TABER LONG TERM...RJS AVIATION...RJS MARINE...NEILES

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