FXUS61 KBUF 241536
AFDBUF
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BUFFALO NY
1036 AM EST THU DEC 24 2009
.SYNOPSIS...
HIGH PRESSURE CENTERED JUST WEST OF JAMES BAY WILL MOVE SLOWLY TO
THE EAST AND BRING DRY WEATHER TODAY THROUGH MOST OF CHRISTMAS
MORNING. MEANWHILE...LOW PRESSURE OVER THE LOWER MISSISSIPPI VALLEY
WILL LIFT NORTH ACROSS THE MIDWEST AND SPREAD PRECIPITATION
EAST ACROSS THE AREA CHRISTMAS AFTERNOON. TEMPERATURES WILL BE NEAR
OR JUST ABOVE FREEZING ON CHRISTMAS DAY...WITH AREAS OF FREEZING
RAIN POTENTIALLY IMPACTING TRAVEL.
&&
.NEAR TERM /THROUGH TONIGHT/...
SINCE SUNRISE...SATELLITE IMAGERY HAS SHOWED SOME HOLES STARTING
TO OPEN UP IN THE LOW CLOUD DECK THAT BLANKETED THE CWA
OVERNIGHT. AS OF 15Z...ONE SIZABLE HOLE HAS OPENED UP ACROSS FAR
SOUTHWESTERN NY WITH SOME EVIDENCE OF THINNING IN THE CLOUDS AS
FAR NORTH AS THE BUFFALO AREA...WITH OTHER BREAKS SHOWING UP
ACROSS FAR SOUTHEASTERN ONTARIO...EASTERN LAKE ONTARIO...AND THE
NORTH COUNTRY.
GIVEN THAT THE LAYER OF MOISTURE SUPPORTING THESE LOW CLOUDS IS
RELATIVELY THIN AND SHOULD GET EVEN THINNER TODAY WITH CONTINUED
SUBSIDENCE FROM ALOFT AND DAYTIME MIXING...EXPECT THAT MOST AREAS
SHOULD EVENTUALLY SEE SOME LIMITED SUNSHINE DEVELOP BEFORE HIGH
CLOUDS BEGIN ARRIVING FROM THE OHIO VALLEY AND CENTRAL LAKES THIS
AFTERNOON. AS SUCH...HAVE ADJUSTED THE SKY GRIDS AND FORECAST
WORDING A BIT TO INDICATE THIS SCENARIO...WITH THE NIAGARA
FRONTIER...SOUTHERN TIER...EASTERN FINGER LAKES...AND NORTH
COUNTRY THE MOST LIKELY AREAS TO SEE SOME LIMITED SUNSHINE
DEVELOP. IN BETWEEN...THE GENESEE VALLEY AND WESTERN FINGER
LAKES WILL PROBABLY SEE THE CLOUDS HOLD IN THE LONGEST.
WITH TEMPS LAGGING A BIT BEHIND FORECAST VALUES...HAVE ALSO
ELECTED TO DROP MAX TEMPS A FEW NOTCHES FROM THE PREVIOUS
FORECAST...WITH MOST AREAS NOW EXPECTED TO SEE HIGHS IN THE
LOWER 30S.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
MAIN FOCUS CONTINUES TO BE ON THE POTENTIAL FOR A MIX OF RAIN AND
FREEZING RAIN ON CHRISTMAS DAY. LOW PRESSURE CENTERED OVER EASTERN
TEXAS EARLY THIS THURSDAY MORNING WILL LIFT SLOWLY TO THE NORTH AND
STALL OVER IOWA CHRISTMAS DAY AND NIGHT. A POTENT LOW LEVEL JET
SURGING AHEAD OF THIS SYSTEM IS ALREADY PRODUCING A VARIETY OF PCPN
EXTENDING FROM THE LOWER MISSISSIPPI VALLEY TO THE UPPER
MIDWEST.
BY THE TIME THE PCPN REACHES OUR CWA FRIDAY...TEMPERATURES ALOFT
(850 TEMPS AVERAGING AROUND +3C) WILL BE WARM ENOUGH FOR RAIN.
THE MAIN QUESTION IS HOW COLD WILL THE SURFACE TEMPERATURES BE WHEN
THE RAIN ARRIVES. THE OPERATIONAL MODELS AND LATEST SREF GUIDANCE
ARE IN GOOD AGREEMENT THAT LIGHT RAIN WILL REACH THE WESTERN
SOUTHERN TIER FRIDAY MORNING...THEN SPREAD NORTHEAST ACROSS THE REST
OF THE AREA DURING THE AFTERNOON...WHILE STAYING JUST WEST OF KART
THROUGH 00Z.
THE LATEST TEMPERATURE GUIDANCE SUGGESTS THAT SURFACE TEMPERATURES
WILL REMAIN AT OR JUST BELOW FREEZING THROUGH MID AFTERNOON ACROSS
THE INTERIOR SECTIONS OF THE SOUTHERN TIER (MAINLY CATTARAUGUS AND
ALLEG ANY COUNTIES). THIS IS THE AREA WHERE THE THREAT FOR FREEZING
RAIN APPEARS TO BE GREATEST FOR CHRISTMAS DAY. TEMPERATURES ACROSS
MOST OF THE REST OF THE CWA ARE EXPECTED TO BE ABOVE FREEZING WHEN
THE RAIN BEGINS.
STEADY RAIN WILL CONTINUE TO SPREAD ACROSS THE AREA CHRISTMAS NIGHT
AS A 50 TO 60 KNOT LOW LEVEL JET TRACKS EAST ACROSS THE AREA. THE
MAIN FOCUS FOR FREEZING RAIN WILL SHIFT TO THE HIGHER ELEVATIONS
EAST OF LAKE ONTARIO WHERE SURFACE TEMPERATURES MAY STAY BELOW
FREEZING MOST OF THE NIGHT.
ON SATURDAY...AN OCCLUDED FRONT THAT EXTENDS WELL EAST OF THE PARENT
LOW IS FORECAST TO PUSH EAST ACROSS WESTERN AND CENTRAL NEW YORK.
EXPECT THE STEADIEST RAIN TO TAPER OFF FROM WEST TO EAST DURING THE
AFTERNOON AS A DRY SLOT WORKS IN BEHIND THE FRONT. STILL LOOKS LIKE
RAIN WILL BE THE DOMINANT PCPN TYPE...BUT A FEW POCKETS OF FREEZING
RAIN MAY LINGER EAST OF LAKE ONTARIO WHERE TEMPERATURES MAY HOVER
AROUND 32.
AS COLDER AIR WORKS IN FROM THE WEST SATURDAY NIGHT...LINGERING RAIN
SHOWERS WILL GRADUALLY CHANGE TO SNOW. THE GFS BRINGS THE COLDER AIR
IN FASTER THAN THE NAM AND ECMWF. FOLLOWING THE TREND OF THESE TWO
MODELS...WILL DELAY THE CHANGEOVER TO SNOW UNTIL A LITTLE AFTER
MIDNIGHT.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
THE UPPER LOW PASSES NEAR THE REGION SUNDAY...BRINGING A CHANCE OF
SNOW SHOWERS. DEPENDING ON THE TRACK OF THE UPPER LOW...MAY ALSO SEE
LAKE EFFECT KICK IN ON A SOUTHWEST FLOW AS 850 MB TEMPS DROP TO
ABOUT -11C RESULTING IN MARGINAL LAKE INDUCED CAPES. THE UPPER LOW
MOVES EAST ON MONDAY...AND INTO THE MARITIMES TUESDAY...BRINGING
PROGRESSIVELY COLDER AIR INTO THE REGION. ON TUESDAY...850 MB
TEMPERATURES MAY DIP TO INTO THE MINUS LOWER 20S BEHIND A PASSING
COLD FRONT. CORRESPONDING SURFACE TEMPERATURES MAY STRUGGLE TO GET
ABOVE 20.
IN TERMS OF THE POTENTIAL FOR LAKE EFFECT SNOW...EXACT WIND
DIRECTIONS ARE HARD TO PIN DOWN. GENERALLY EXPECT SW WINDS TO SHIFT
MORE NW WITH TIME.
HIGH PRESSURE BUILDS IN ON WEDNESDAY...WITH A CONTINUATION OF COLD
TEMPERATURES...BUT DIMINISHING CHANCES FOR PRECIPITATION.
&&
.AVIATION /15Z THURSDAY THROUGH MONDAY/...
SINCE SUNRISE...SATELLITE IMAGERY HAS SHOWED SOME HOLES STARTING
TO OPEN UP IN THE LOW CLOUD DECK THAT BLANKETED THE CWA
OVERNIGHT. AS OF LATE MORNING...ONE SIZABLE HOLE HAS OPENED UP
ACROSS FAR SOUTHWESTERN NY WITH SOME EVIDENCE OF THINNING IN THE
CLOUDS AS FAR NORTH AS THE BUFFALO AREA...WITH OTHER BREAKS
SHOWING UP ACROSS FAR SOUTHEASTERN ONTARIO...EASTERN LAKE
ONTARIO...AND THE NORTH COUNTRY.
GIVEN THAT THE LAYER OF MOISTURE SUPPORTING THESE LOW CLOUDS IS
RELATIVELY THIN AND SHOULD GET EVEN THINNER TODAY WITH CONTINUED
SUBSIDENCE FROM ALOFT AND DAYTIME MIXING...EXPECT THAT MOST AREAS
SHOULD EVENTUALLY SEE SOME GRADUAL IMPROVEMENT TO MVFR AND
EVENTUALLY VFR AS THE DAY WEARS ON. MID LEVEL CEILINGS WILL THEN
DEVELOP AFTER 00Z TONIGHT.
OUTLOOK...
FRIDAY...VFR/MVFR CONDITIONS EARLY DETERIORATE TO 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.
&&
.MARINE...
SMALL CRAFT ADVISORIES HAVE BEEN DISCONTINUED. WINDS WILL CONTINUE
TO DIMINISH THROUGH TONIGHT AS HIGH PRESSURE RIDGES IN. SMALL CRAFT
ADVISORY CONDITIONS ARE LIKELY TO DEVELOP FRIDAY AND SATURDAY AS LOW
PRESSURE APPROACHES FROM THE MIDWEST.
&&
.BUF WATCHES/WARNINGS/ADVISORIES...
NY...NONE.
MARINE...NONE.
&&
$$
SYNOPSIS...TJP
NEAR TERM...JJR/TMA
SHORT TERM...TJP
LONG TERM...APFFEL/TJP
AVIATION...JJR/TMA
MARINE...TJP
