Issued by NWS Burlington, VT
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000 FXUS61 KBTV 220157 AFDBTV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BURLINGTON VT 857 PM EST SAT NOV 21 2009 .SYNOPSIS... HIGH PRESSURE ACROSS THE GREAT LAKES AND OHIO VALLEY STATES WILL BUILD SLOWLY EAST TONIGHT AND SETTLE ACROSS THE NORTHEAST ON SUNDAY INTO MONDAY. THEREFORE...OUTSIDE ANY LINGERING CLOUDS ACROSS THE AREA THIS EVENING...EXPECT GENERALLY FAIR AND DRY WEATHER DURING THE PERIOD AS TEMPERATURES REMAIN ON THE MILD SIDE. THE NEXT CHANCE OF SIGNIFICANT PRECIPITATION WILL OCCUR BY THE MIDDLE TO LATER PORTIONS OF NEXT WEEK AS LOW PRESSURE TRACKS EAST FROM THE CENTRAL PLAINS. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... AS OF 850 PM EST SATURDAY...HAVE MADE MINOR ADJUSTMENTS TO SKY AND TEMPERATURE FORECAST TO ACCOUNT FOR PERSISTENT LAYER OF STRATOCUMULUS CLOUDS BETWEEN 1500 AND 2500 FT AGL. WHILE SIGNIFICANT CLEARING HAS OCCURRED THIS EVENING ACROSS THE CHAMPLAIN VALLEY AND MUCH OF ERN/SERN VT...OVERCAST CONDITIONS PREVAIL ACROSS ALL OF THE NRN ADIRONDACKS...THE ST. LAWRENCE VALLEY...AND PORTIONS OF N-CENTRAL AND NERN VT. WITH WEAK WINDS OVERNIGHT AND SUBSIDENCE ALOFT...IT WILL BE DIFFICULT TO ELIMINATE EXISTING CLOUDS TRAPPED BELOW SUBSIDENCE INVERSION. AS SUCH...HAVE INCREASED CLOUDS FOR SEVERAL ADDITIONAL HRS...WITH A SLOW DECREASING TREND TOWARD DAYBREAK. FOG MAY BE LIMITED ACROSS NRN NY OWING TO OVC SKIES...BUT ELSEWHERE DEWPOINT DEPRESSIONS ARE SMALL /WITH DEWPOINTS GENERALLY IN THE 30S/ AND SOME RADIATIONAL COOLING WILL BE FAVORED...ESPECIALLY WITH LONG MID-NOVEMEBER NIGHT. PATCHY FOG REMAINS POSSIBLE...ESPECIALLY IN AREAS WITH MOSTLY CLEAR SKIES. MINIMUM TEMPERATURES WILL BE FAIRLY MILD BY LATE NOVEMBER STANDARDS...WITH READINGS MAINLY IN THE UPPER 20S TO LOWER 30S ACROSS MOST PORTIONS OF THE NORTH COUNTRY. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... AS OF 217 PM EST SATURDAY...TRANQUIL AND MILD LATE FALL WEATHER THEN CONTINUES THROUGH THE REMAINDER OF THE SHORT TERM AS AFOREMENTIONED HIGH PRESSURE BUILDS ATOP THE NORTHEAST DURING SUNDAY/MONDAY TIME FRAME. THEREFORE EXPECT FAIR AND DRY CONDS THROUGH THE PERIOD ALONG WITH A FAIRLY WIDE DIURNAL RANGE IN TEMPS. WITH SHALLOW NATURE OF PBL THIS TIME OF YEAR DAYTIME TEMPS WILL BE RATHER UNIFORM... SLIGHTLY MILDER PERHAPS AT THE HIGHER ELEVATIONS WHERE SHALLOW PBL MIXING MAY BE ABLE TO TAP INTO WARMER 925 MB TEMPS ALOFT. NIGHTTIME LOWS WILL BE NEAR SEASONAL NORMS...THOUGH WITH AT LEAST SOME RADIATIVE EFFECTS EXPECTED...HAVE UNDERCUT MOS MINS TEMPS SLIGHTLY DURING OVERNIGHT PERIODS. BY MONDAY NIGHT...SOME DISAGREEMENT BEGINS TO CREEP INTO THE MODELS AS DEEPER MOISTURE ACROSS THE SOUTHEAST/WRN ATLANTIC ATTEMPTS TO CREEP NORTHWARD BENEATH WESTERN EXTENSION OF DEPARTING RIDGE AXIS. AT THIS TIME BELIEVE ANY DEEPER MOISTURE WILL HAVE A TOUGH TIME REACHING THIS FAR NORTH GIVEN PLACEMENT OF LL RIDGE AXIS...AND WITH BROAD SUPPORT FROM THIS MORNINGS OP ECMWF RUN AND GFS MEAN ENSEMBLES HAVE KEPT SENSIBLE CONDS ESSENTIALLY DRY THROUGH 12Z TUESDAY. MID TO UPPER LVL CLOUDS WILL LIKELY BE ON THE INCREASE HOWEVER IN UPPER ANTICYCLONIC FLOW...THUS HAVE KEPT OVERNIGHT MIN TEMPS SLIGHTLY MILDER THAN PRIOR COUNTERPARTS. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 345 PM EST SATURDAY...THE FORECAST AREA WILL BE BETWEEN TWO LOW PRESSURE SYSTEMS ON TUESDAY...WITH ONE SYSTEM SOUTHEAST OF CAPE COD AND ANOTHER SYSTEM APPROACHING THE WESTERN GREAT LAKES. MODELS SHOW AREA WILL HAVE A WEAK RIDGE OF HIGH PRESSURE OVER THE REGION TUESDAY AND TUESDAY NIGHT...EXTENDING INTO MIDDAY ON WEDNESDAY. WILL GO WITH A MAINLY DRY FORECAST TUESDAY THROUGH MIDDAY ON WEDNESDAY. HOWEVER...WILL HAVE SLIGHT CHANCE POPS FOR TUESDAY FOR RAIN SHOWERS ACROSS SOUTH CENTRAL VERMONT. HAVE GONE BELOW GMOS POP GUIDANCE FOR TUESDAY AND TUESDAY NIGHT...AS WELL AS FOR WEDNESDAY. AN UPPER LOW OVER THE GREAT LAKES WILL MOVE ACROSS THE AREA LATE WEDNESDAY AND WEDNESDAY NIGHT...BRINGING A CHANCE FOR SOME RAIN SHOWERS. THANKSGIVING DAY...MODELS SHOW A DIGGING UPPER TROUGH AND CLOSED UPPER LOW OVER THE WESTERN GREAT LAKES ON THURSDAY. LOOKS LIKE THE FORECAST AREA WILL REMAIN DRY...BUT WITH MOSTLY CLOUDY SKIES EXPECTED. HAVE PUT IN SLIGHT CHANCE POPS FOR RAIN SHOWERS ON THANKSGIVING DAY... BUT GENERALLY FEEL THE DAYTIME WILL BE MAINLY DRY. HAVE GONE BELOW GMOS POPS FOR THANKSGIVING DAY. GFS MODEL IS FASTER THAN THE ECMWF MODEL IN BRINGING THE DIGGING UPPER TROUGH AND CLOSED UPPER LOW EASTWARD. GIVEN THE FACT THAT THE UPPER TROUGH IS DIGGING SOUTHWARD AND BUILDING THE UPPER RIDGE EAST OF IT...WOULD TEND TO FAVOR THE SLOWER ECMWF...AS FEEL THE GFS LOOKE A TAD TOO FAST. WILL MENTION A CHANCE OF SHOWERS THURSDAY NIGHT. WILL MENTION RAIN OR SNOW ON FRIDAY... AS BOTH THE GFS AND ECMWF SUGGEST IT WILL BE WARM ENOUGH ALOFT FOR SOME RAIN ON FRIDAY...BUT CHANGING TO SNOW LATER IN THE DAY ON FRIDAY. THE ECMWF SHOWS A CLOSED 500 MB LOW WILL MOVE ACROSS THE REGION FRIDAY NIGHT WHICH WILL RESULT IN DYNAMIC COOLING ALOFT. ECMWF SUGGESTS SOME SIGNIFICANT WRAP AROUND PRECIPITATION IS POSSIBLE FRIDAY NIGHT. THIS WILL HAVE TO BE WATCHED CLOSELY. HOWEVER...GIVEN MODEL DIFFERENCES IN TIMING...CONFIDENCE LEVEL IS FAIR AT THIS TIME. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... THROUGH 00Z MONDAY...VFR/MVFR WITH FAIRLY TRANQUIL WEATHER EXPECTED FOR THE FIRST 24 HOURS. HIGH PRESSURE SETTLING OVER THE REGION HAS ALLOWED SKIES TO BECOME CLEAR IN SOME AREAS THIS EVENING. HOWEVER...A STRONG SUBSIDENCE INVERSION HAS TRAPPED A SHALLOW LAYER OF MOISTURE AT LOW LEVELS WHICH HAS KEPT LOW CLOUDS ACROSS MUCH OF NORTHERN NEW YORK AND THE WESTERN SLOPES OF THE GREEN MOUNTAINS. AS TEMPERATURES COOL AND APPROACH THE DEWPOINT OVERNIGHT...LOW CLOUDS WILL FILL IN AT MOST SITES ALONG WITH PATCHY FOG. CEILINGS WILL GENERALLY BE 1500-2500 FT AFTER MIDNIGHT ALTHOUGH KSLK WILL DROP BELOW 1000 FT LATE TONIGHT. VISIBILITIES WILL RANGE FROM 3 TO 5 SM WITH 2 SM AT KMPV. THE LOWEST CONDITIONS WILL OCCUR 08Z-12Z. THEREAFTER EXPECT FOG AND CEILINGS TO SLOWLY THIN AND LIFT AND ALL SITES WILL RETURN TO VFR BY 15Z. WINDS WILL BE LIGHT AND VARIABLE THROUGH THE PERIOD. OUTLOOK 00Z MONDAY THROUGH THURSDAY... SUNDAY NIGHT THROUGH TUESDAY NIGHT...VFR UNDER HIGH PRESSURE. INCREASING CLOUDS MONDAY AND TUESDAY. WEDNESDAY THROUGH THURSDAY...VFR DIMINISHING TO MVFR IN RAIN AND MOUNTAIN SNOW SHOWERS AS LOW PRESSURE SWINGS THROUGH THE GREAT LAKES. OCCASIONAL IFR POSSIBLE IN ANY SNOW. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...NONE. NY...NONE. && $$ SYNOPSIS...JMG NEAR TERM...BANACOS SHORT TERM...JMG LONG TERM...WGH AVIATION...MB
