FXUS61 KBUF 242045
AFDBUF
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BUFFALO NY
345 PM EST THU DEC 24 2009
.SYNOPSIS...
HIGH PRESSURE RIDGING SOUTHWARD FROM CANADA WILL KEEP THINGS DRY
INTO CHRISTMAS MORNING. LOW PRESSURE NEAR IOWA WILL SLOWLY LIFT A
FRONTAL BOUNDARY ACROSS THE REGION...BRINGING PRECIPITATION INTO THE
REGION CHRISTMAS AFTERNOON AND NIGHT. TEMPERATURES WILL BE JUST
ABOVE FREEZING IN MOST LOCATIONS...HOWEVER EXPECT POCKETS OF
FREEZING RAIN MAINLY IN THE SOUTHERN TIER AND NORTH COUNTRY.
&&
.NEAR TERM /THROUGH FRIDAY/...
AS OF 20Z...THE LOW CLOUDS SLOWLY CONTINUE TO ERODE ACROSS WESTERN
AND EASTERN PORTIONS OF THE AREA. ACROSS THE WEST...A RATHER
PRONOUNCED CLEARING LINE HAS PROGRESSED TO ROUGHLY A NIAGARA
FALLS-DANSVILLE LINE...WHILE THE NORTH COUNTRY IS SEEING THE
CLEARING SLOWLY SPREAD FROM THE HIGHER ELEVATIONS TO THE LOWER
ELEVATIONS...A TESTAMENT TO EXACTLY HOW LOW AND SHALLOW THE LAYER OF
LOW LEVEL MOISTURE ACTUALLY IS. IN BETWEEN...LOW CLOUDS HANG TIGHT
ACROSS MUCH OF THE GENESEE VALLEY AND FINGER LAKES.
WITH CONTINUED SUBSIDENCE AND ENTRAINMENT OF DRIER AIR FROM
ABOVE...FEEL THAT THIS AREA OF LOW CLOUDS WILL CONTINUE TO GRADUALLY
SHRINK UP FROM ITS EDGES INWARD LATE THIS AFTERNOON AND
EVENING...THOUGH EXACTLY HOW FAR THIS SHRINKING TREND WILL GET IS
STARTING TO BECOME MORE UNCERTAIN GIVEN THAT WE WILL BE LOSING
DIURNAL HEATING IN A FEW MORE HOURS. FOR NOW WILL HOLD THE LOW
CLOUDS IN ACROSS THE GENESEE VALLEY AND FINGER LAKES REGION INTO
THIS EVENING...WITH THE MATTER THEN BECOMING MORE OF A MOOT POINT
THEREAFTER AS MID AND HIGH CLOUDINESS OVERSPREADS THE REGION FROM
THE OHIO VALLEY AND CENTRAL GREAT LAKES. ALL OF THIS WILL ADD UP TO
SKIES EITHER GENERALLY REMAINING MOSTLY CLOUDY OR BECOMING SO DURING
THE COURSE OF THIS EVENING...WITH SOME TEMPORARY THINNING OF THE MID
AND HIGH CLOUDS THEN BECOMING POSSIBLE LATER ON TONIGHT. ANY
PRECIPITATION STILL LOOKS TO REMAIN SAFELY TO OUR WEST THROUGH THE
NIGHT...SO WILL CONTINUE TO CARRY A DRY FORECAST THROUGH THE NIGHT.
THEN ON CHRISTMAS DAY...A GRADUAL WEST TO EAST DETERIORATION IN THE
WEATHER WILL TAKE PLACE AS WARM AIR ADVECTION INCREASES OUT AHEAD OF
SLOW-MOVING LOW PRESSURE OVER THE MISSISSIPPI VALLEY. IN THE
PRESENCE OF INCREASING MOISTURE...FORCING FROM THE WARM ADVECTION
PATTERN AND ASSOCIATED LOW LEVEL JET WILL EVENTUALLY LEAD TO
PRECIPITATION BREAKING OUT ACROSS FAR SOUTHWESTERN NEW YORK BY
MID-LATE MORNING...BEFORE SLOWLY SPREADING NORTHWARD AND EASTWARD
ACROSS MOST AREAS SOUTH OF LAKE ONTARIO BY EARLY EVENING. THIS
TIMING IS SLIGHTLY FASTER THAN THAT ADVERTISED BY THE FASTER AND
FAIRLY CONSISTENT GFS...WHICH FROM PAST EXPERIENCE TYPICALLY TENDS
TO HAVE A MUCH BETTER HANDLE ON THE ARRIVAL TIME OF WARM ADVECTIVE
PRECIP THAN THE NAM. THE LATTER MODEL HAS SLOWED A GOOD 3-4 HOURS
FROM ITS PREVIOUS CONTINUITY WITH ITS 12Z RUN...A SOLUTION THAT I AM
AT LEAST SOMEWHAT SKEPTICAL OF AT THIS TIME. WILL CONTINUE TO BRING
HIGH LIKELY TO CATEGORICAL POPS TO AREAS SOUTH OF LAKE ONTARIO
DURING THE DAY...TAPERING SHARPLY TO CHANCE ACROSS THE EASTERN
FINGER LAKES AND OSWEGO COUNTY...AND SLIGHT CHANCE OR LOWER ACROSS
THE NORTH COUNTRY...WHICH SHOULD REMAIN DRY THROUGH THE DAY.
AS HAS BEEN THE CASE FOR MUCH OF THIS WEEK...THE BIG ISSUE WITH THIS
SYSTEM IS THE PTYPE...AND ITS POTENTIAL IMPACT ON HOLIDAY TRAVEL.
ALL MODEL GUIDANCE CONTINUES TO SUGGEST A GOOD LAYER OF WARM AIR
WORKING IN ALOFT...WITH 850 MB TEMPS CLIMBING INTO THE +2C TO +6C
RANGE PRIOR TO THE ONSET OF THE PRECIP. THIS WILL BE PLENTY WARM
ENOUGH FOR THE PCPN TO BEGIN AS LIQUID...WITH BOUNDARY LAYER
TEMPERATURES AND EVAPORATIVE COOLING PROCESSES THEN CONTROLLING WHAT
HAPPENS AFTERWARD.
AT THIS JUNCTURE...IT APPEARS THAT THE COMBINATION OF THE LATER
START TIME WILL ALLOW FOR ENOUGH WARMING OF THE BOUNDARY LAYER TO
KEEP THE PRECIPITATION IN THE FORM OF PLAIN RAIN ACROSS THE NIAGARA
FRONTIER AND FINGER LAKES...ESPECIALLY IN THE BUFFALO AND ROCHESTER
AREAS. WHILE WE CANNOT TOTALLY RULE OUT SOME BRIEF ISOLATED POCKETS
OF FREEZING RAIN FURTHER SOUTH ACROSS FAR SOUTHERN ERIE/WYOMING/
LIVINGSTON/ONTARIO COUNTIES...THESE APPEAR TO BE FAR TOO LIMITED TO
WARRANT ANY FLAG AT THIS TIME.
FURTHER TO THE SOUTH ACROSS THE SOUTHERN TIER...IT WILL BE A BIT OF
A DIFFERENT STORY AS SURFACE TEMPERATURES WILL REMAIN COLDER
INITIALLY...ENOUGH TO ALLOW FOR A HIGHER PROBABILITY OF FREEZING
RAIN...ESPECIALLY ACROSS INTERIOR SECTIONS. IN ADDITION...PROFILES
FROM THE NAM/GFS ALSO NOW SUGGEST AN INCREASING POTENTIAL FOR ENOUGH
EVAPORATIONAL COOLING OF THE COLUMN AT PRECIP ONSET TO POSSIBLY
RESULT IN A CHANGE FROM RAIN/FREEZING RAIN BACK OVER TO SLEET AND
SNOW FOR A TIME...PARTICULARLY FROM CATTARAUGUS COUNTY EASTWARD
WHERE THE AIRMASS WILL BE A FEW DEGREES COLDER TO START. SHOULD THIS
OCCUR...WE COULD BE LOOKING AT PRECIPITATION STARTING AS RAIN/
FREEZING RAIN IN THIS AREA...THEN CHANGING TO A SNOW/SLEET MIX FOR A
WHILE...BEFORE GOING BACK TO FREEZING RAIN AND THEN EVENTUALLY RAIN
AS WARM ADVECTION WARMS THE LOWER LAYERS BACK ABOVE FREEZING.
WITH THE ABOVE IN MIND AND THROUGH EXTENSIVE COLLABORATION WITH
SURROUNDING WFO'S...WE HAVE ELECTED TO HOIST A WINTER WEATHER
ADVISORY FOR THE SOUTHERN TIER FROM 12Z FRIDAY TO 00Z SATURDAY. THIS
WILL COVER THE POTENTIAL FOR THE DIFFERENT PRECIPITATION TYPES
MENTIONED ABOVE...AS WELL AS THE POSSIBILITY OF UP TO A TENTH OF AN
INCH OR SO OF ICING FROM ANY FREEZING RAIN. BY EARLY EVENING...
EXPECT BOUNDARY LAYER TEMPS TO BE WARM ENOUGH TO ALLOW FOR ALL RAIN
EVERYWHERE.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
WITH ONE NOTABLE EXCEPTION...EXPECT TEMPERATURES TO REMAIN ABOVE
FREEZING IN MOST OF WESTERN NEW YORK ON FRIDAY NIGHT AND SATURDAY.
THIS SAID...TEMPERATURES WILL REMAIN IN THE 30S IN MOST LOCATIONS
THROUGH THIS ENTIRE EVENT...SO THERE IS NOT MUCH MARGIN FOR
ERROR...LEAVING OPEN THE POSSIBILITY OF PATCHY OF FREEZING RAIN
LINGERING INTO FRIDAY NIGHT.
THERE WILL BE TWO MAIN FEATURES THAT LIFT ACROSS THE REGION...FIRST
AN AREA OF MID LEVEL WARM AIR ADVECTION...WHICH WILL CONTINUE TO
LIFT FROM SOUTHWEST TO NORTHEAST FRIDAY NIGHT...AS IT WEAKENS. THE
SECOND WAVE WILL BE ASSOCIATED WITH A WEAK COASTAL LOW WHICH
DEVELOPS ALONG A SLOW MOVING OCCLUDED FRONT. THIS WILL ENTER THE
SOUTHERN TIER SATURDAY MORNING...AGAIN LIFTING TO THE NE INTO THE
NORTH COUNTRY SATURDAY NIGHT. NOTED THE NAM SEEMS TO UNDERDO THIS
SECOND FEATURE...ESPECIALLY WHEN COMPARED TO THE UKMET/GEM WHICH
BOTH BRING AROUND .50 OF QPF SATURDAY INTO SATURDAY NIGHT. WITH GFS
IN LINE WITH THE LATTER TWO...CONSENSUS LEANS TOWARDS A SECOND ROUND
OF PRECIP...WITH CATEGORICAL POPS.
ONTO THE EXCEPTION...COLD AIR DAMMING MAY BE AN ISSUE IN THE
NORTH COUNTRY...AS AIR FUNNELS DOWN THE ST LAWRENCE VALLEY. THE AREA
OF CONCERN IS NORTHERN PORTIONS OF JEFFERSON AND LEWIS
COUNTIES...WHERE THE TOPOGRAPHY LENDS ITSELF TO FUNNELING AIR DOWN
THE ST LAWRENCE VALLEY. SIGNIFICANT UNCERTAINTY REMAINS...BUT CAN
SEE A REAL POTENTIAL FOR A QUARTER INCH (OR MORE) OF ICE IN THIS
AREA. THE SIGNIFICANT UNCERTAINTY AND BUSY TRAVEL PERIOD POINT TO A
WATCH FOR THIS AREA...WITH LOCATIONS CLOSEST TO THE ST LAWRENCE
THE MAIN CONCERN. BASED ON THIS...WILL ISSUE A WINTER STORM WATCH
FOR THESE TWO COUNTIES.
ON SATURDAY NIGHT...THE OCCLUDED FRONT SLOWLY MAKES ITS WAY
EASTWARD...WITH PRECIPITATION ENDING FROM WEST TO EAST. FREEZING
RAIN WILL BE A LINGERING CONCERN IN THE NORTH COUNTRY...HOWEVER THIS
BAND WILL BE MAINLY A RAIN PRODUCER. WHILE COLDER AIR WORKS IN
BEHIND THE FRONT...EXPECT PRECIPITATION SHOULD LARGELY BE OVER BY
THE TIME COLD AIR DOES GET IN. ANY PRECIPITATION THAT DOES FALL
WOULD BE A CONCERN SINCE THERE IS GENERALLY TOO WARM ALOFT FOR
CRYSTAL GROWTH...WITH FREEZING RAIN/DRIZZLE A POSSIBILITY. THIS
SAID...WITH A MINIMAL CHANCE FOR PRECIPITATION...WILL FORECAST RAIN
ENDING...THEN TEMPERATURES DROPPING. TOO FAR OFF TO PIN DOWN
SPECIFICS...BUT SOMETHING TO MONITOR IF THIS FORECAST HOLDS.
ON SUNDAY AND SUNDAY NIGHT...TEMPERATURES DO COOL AT ALL LEVELS BEHIND
THE BOUNDARY...TRANSITIONING ANY PRECIPITATION TO SNOW. LAKE EFFECT
SET UP IS MARGINAL...WITH 850 MB TEMPS ONLY AROUND -10 C...THERE
WILL BE LIMITED INSTABILITY. HOWEVER...THE UPPER LOW CROSSING THE
REGION WILL BRING A CHANCE OF SNOW SHOWERS TO ALL...WITH SLIGHTLY
HIGHER POPS CARRIED NORTHEAST OF THE LAKES...GIVEN THE LIMITED LAKE
EFFECT POTENTIAL. TEMPERATURES WILL BE SLOW TO RISE...ONLY REACHING
THE LOWER 30S ON SUNDAY.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
THE UPPER LEVEL LOW ASSOCIATED WITH THE WINTRY WEATHER ACROSS THE
PLAINS AND TOWARDS THE EAST COAST OVER THE CHRISTMAS WEEKEND WILL
CONTINUE TO ADVANCE EASTWARD MONDAY. THE 12Z GLOBAL MODELS SUITE OF
THE ECMWF...GFS AND GEM ALL PLACE THIS UPPER LEVEL LOW NEAR WESTERN
NEW YORK AND WESTERN PA MONDAY MORNING. THIS UPPER LEVEL LOW WILL
SUPPORT SNOW SHOWERS ACROSS THE REGION...WITH LIKELY POPS DOWNWIND
OF THE TWO GREAT LAKES. A WESTERLY FLOW WILL KEEP LES SOUTH OF THE
METRO BUFFALO AREA MONDAY...WHILE AHEAD OF THE UPPER LEVEL LOW A
SOUTHWESTERLY FLOW WILL BRING SNOW INTO THE METRO WATERTOWN AREA
BEFORE SINKING SOUTHWARD THROUGH THE DAY.
AS THIS UPPER LEVEL LOW PASSES TO THE EAST COLDER AIR ALOFT WILL
CONTINUE TO POUR ACROSS THE REGION FROM THE NORTHWEST. A SHARP
TEMPERATURE GRADIENT AT 850 WILL PASS ACROSS THE REGION EARLY MONDAY
NIGHT WHICH MAY LEAD TO A QUICK BURST OF MODERATE SNOW AS THE SFC
AND UPPER LEVEL COLD FRONT PASS ACROSS THE REGION. BY TUESDAY
MORNING 850S WILL BE DOWN TO -18 TO -22 ACROSS THE CWA.
WINDS WILL BECOME MORE NORTHWESTERLY TUESDAY AND TUESDAY NIGHT WITH
LES ACROSS SKI COUNTY AND TO THE SOUTH AND EAST OF LAKE ONTARIO. AS
A SFC HIGH PRESSURE NEARS THE REGION FROM THE WEST THIS LES WILL
DIMINISH FIRST OFF LAKE ERIE AND LATER OFF LAKE ONTARIO. SFC
TEMPERATURES TUESDAY WILL RANGE 10 TO 15 DEGREES BELOW NORMAL WITH
MANY PLACES STRUGGLING TO MAKE IT OUT OF THE 20S.
DRY WEDNESDAY WITH SFC HIGH PRESSURE ANCHORED OVER THE MID-ATLANTIC
STATES. REMAINING COLD ALTHOUGH A LITTLE MORE SUNSHINE IS EXPECTED
AS UPPER LEVEL MOISTURE DECREASES.
MODELS SHOW ANOTHER DISTURBANCE IN THE SOUTHERN BRANCH OF THE JET
STREAM FOR LATE NEXT WEEK. FOR NOW WILL JUST GO WITH A LOW CHC POP
AS MODELS WILL LIKELY VARY THEIR SOLUTION BASED ON HOW AND IF THE
NORTHERN BRANCH OF THE JET STREAM INTERACTS WITH THE TIMING OF THIS
FEATURE.
&&
.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
WITH CONTINUED SUBSIDENCE AND DAYTIME MIXING OF THE LOW LEVELS...THE
LOW CLOUDS CONTINUE TO ERODE FROM THE SOUTHWEST AND NORTHEAST
EARLY THIS AFTERNOON...WITH CONDITIONS ALREADY HAVING IMPROVED TO
VFR ACROSS AREAS TO THE SOUTH AND WEST OF BUFFALO...AND ACROSS
PORTIONS OF THE NORTH COUNTRY. EXPECT THIS GENERAL TREND TO
CONTINUE THE REMAINDER OF THE AFTERNOON AND EARLY EVENING...WITH
MOST LOCATIONS LIKELY GOING VFR BY 00Z OR SHORTLY THEREAFTER. VFR
CONDITIONS ARE THEN ANTICIPATED TO PERSIST THROUGH THE NIGHT AND
INTO EARLY CHRISTMAS DAY UNDER INCREASING MID AND HIGH-LEVEL
CLOUDS.
AS WE GET INTO CHRISTMAS MORNING...CONDITIONS WILL BEGIN TO SLOWLY
DETERIORATE ACROSS WESTERN SECTIONS OF THE AREA AS WARM AIR ADVECTION
INCREASES OUT AHEAD OF LOW PRESSURE OVER THE MISSISSIPPI VALLEY.
EXPECT PRECIPITATION TO BREAK OUT ACROSS FAR SOUTHWESTERN NY STATE
BY AROUND 15Z...AND TO APPROACH KBUF/KIAG/KDSV BY THE END OF THE
TAF PERIOD. THE PREDOMINANT PTYPE AT THIS POINT IS EXPECTED TO BE
RAIN...WHICH WILL BE MIXED WITH AREAS OF SNOW/SLEET/FREEZING RAIN
ACROSS THE WESTERN SOUTHERN TIER.
OUTLOOK...
FRIDAY NIGHT...IFR/MVFR IN RAIN AND PATCHY FREEZING RAIN.
SATURDAY...IFR/MVFR WITH RAIN CHANGING TO SNOW FROM WEST TO EAST.
SUNDAY AND MONDAY...MVFR/VFR WITH A CHANCE OF SNOW SHOWERS...WITH
LIMITED LAKE SNOWS POSSIBLE EAST OF THE LAKES.
TUESDAY...MVFR/VFR WITH A CHANCE OF SNOW SHOWERS.
&&
.MARINE...
ON LAKE ERIE...SOUTHEAST WINDS PICK UP TONIGHT AND FRIDAY. EXPECT
LOCALLY LOWER WINDS ALONG THE CHAUTAUQUA RIDGE INTO FRIDAY...TO
EVENTUALLY MIX DOWN. EXPECT WINDS WILL BE STRONG ENOUGH TO ISSUE A
SMALL CRAFT ADVISORY...THOUGH WAVES WILL NOT BE TERRIBLY LARGE GIVEN
THE SHORT FETCH...THEY WILL BE CHOPPY. WINDS DIMINISH AND SHIFT SW
THROUGH THE WEEKEND.
ON LAKE ONTARIO...A E-NE FLOW DEVELOPS TONIGHT...LASTING THROUGH
SATURDAY. 925 MB WINDS ARE STRONG...BUT NOT LINED UP WELL AT ALL
WITH SURFACE...SO EXPECT MUCH OF THIS NOT TO MIX DOWN THROUGH THE
INVERSION. FOR THIS REASON GO WITH A STRONG SMALL CRAFT INSTEAD OF
GALES...CAPPING WINDS AT 30 KTS. WAVES SHOULD BUILD WELL ON WESTERN
ONTARIO...WITH THE SCA LIKELY LASTING WELL INTO SATURDAY.
LOOKING AHEAD...THE PASSAGE OF A FRONTAL BOUNDARY LATE MONDAY...MAY
PRODUCE GALES OR STRONG SCA CONDITIONS.
&&
.BUF WATCHES/WARNINGS/ADVISORIES...
NY...WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH LATE
SATURDAY NIGHT FOR NYZ007-008.
WINTER WEATHER ADVISORY FROM 7 AM TO 7 PM EST FRIDAY FOR
NYZ019>021.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM FRIDAY TO 4 AM EST SATURDAY FOR
LEZ040-041.
SMALL CRAFT ADVISORY FROM 6 AM FRIDAY TO 6 AM EST
SATURDAY FOR LOZ043.
SMALL CRAFT ADVISORY UNTIL 6 AM EST SATURDAY FOR LOZ042.
&&
$$
SYNOPSIS...APFFEL
NEAR TERM...JJR
SHORT TERM...APFFEL
LONG TERM...THOMAS
AVIATION...JJR
MARINE...APFFEL/JJR/THOMAS
