WINTER ANALOGS FOR 2009-2010 WINTER
TIME ALWAYS MARCHES ON AND ITS TIME ONCE AGAIN FOR OUR SEMI-ANNUAL
ANALOG FEST OF TRYING TO COMPARE THIS AUTUMN`S TEMPERATURES AND ENSO
STATE WITH SIMILAR INSTANCES IN THE PAST.

THIS UPCOMING WINTER WILL FEATURE EL NINO CONDITIONS IN THE TROPICAL
PACIFIC. MODEL CONSENSUS IS FOR A MODERATE TYPE EL NINO TO OCCUR.
THE LAST TWO WINTERS THAT HAD MODERATE EL NINOS WERE 2002-3 AND
2006-7, ALMOST POLAR OPPOSITE WINTERS IN SPITE OF BEING IN THE SAME
CATEGORY. THE 2002-3 EL NINO WAS MORE WEST BASED THAN 2006-7. THE
2002-3 EL NINO HAD A PACIFIC DECADAL OSCILLATION (PDO) THAT WAS
STRONGLY POSITIVE AND THERE WAS A COLD WATER POOL AROUND
NEWFOUNDLAND. THE 2006-7 EL NINO THE PACIFIC DECADAL OSCILLATION WAS
MORE NEUTRAL, AND THERE WAS A WARM POOL AROUND NEWFOUNDLAND. SO FAR
THIS AUTUMN THE EL NINO DOES LOOK MORE WEST BASED THAN 2006-7, THE
PACIFIC DECADAL OSCILLATION HAS RECENTLY BEEN WEAKLY POSITIVE AND
THERE WAS, BUT NOT AT THE PRESENT MOMENT, A NEWFOUNDLAND WARM POOL.

EARLIER THIS MONTH A WESTERLY WIND BURST ALONG THE EQUATOR CAUSED A
RAPID WARMING OF THE TROPICAL WATERS WHICH BROUGHT THE SEA SURFACE
TEMPERATURE ANOMALIES INTO THE LOW END OF THE STRONG EL NINO
CATEGORY. SINCE THEN SEA SURFACE TEMPERATURE ANOMALIES HAVE
STABILIZED. AS PER ITS NAME MOST EL NINOS PEAK IN DECEMBER BEFORE
WEAKENING THE REST OF THE WINTER.

OTHER ATMOSPHERIC TELECONNECTIONS ALL AFFECT OUR WEATHER PATTERN.
THE STATE OF THE REST OF THE PACIFIC IS MEASURED BY THE PACIFIC
DECADAL OSCILLATION (PDO) IN THE LONGER TERM AND THE PACIFIC NORTH
AMERICA OSCILLATION (PNA) IN THE SHORTER TERM. ON OUR SIDE OF THE
COAST WE HAVE THE NORTH ATLANTIC OSCILLATION (NAO). WE ARE IN THE
DECADAL CYCLE WHERE THE PDO IS AVERAGING NEGATIVE. THIS DOES NOT
FAVOR PROLONGED RIDGING IN THE EASTERN PACIFIC, A POSITIVE PNA. BUT
IN EL NINO WINTERS, THE PDO CAN AND HAS BECOME POSITIVE AS IT DID
DURING THE WINTERS OF 1982-3 AND 1997-8.

MEANWHILE THE STATE OF THE ATLANTIC AS MEASURED BY THE NAO ALSO
INFLUENCES OUR WEATHER. A POSITIVE NAO GENERALLY FAVORS MILDER
WEATHER WHILE A NEGATIVE NAO FAVORS COLDER AND STORMIER CONDITIONS
ALONG THE EAST COAST. THE OUTLOOK FOR THE NAO FOR THIS UPCOMING
WINTER IS MORE PROBLEMATIC THAN USUAL WITH MANY CONFLICTING
SIGNALS. THE NEWFOUNDLAND WATER POOL AVERAGED WARM DURING THE LATE
SPRING AND SUMMER. USUALLY THE WINTER FOLLOWS SUIT AND IS ONE OF
THE REASONS THAT THE UKMET OUTLOOK FOR THIS UPCOMING WINTER IS FOR
A POSITIVE NAO. BUT, (TU AL) OTHER RESEARCH HAS SHOWN
CORRELATIONS BETWEEN LOWER THAN AVERAGE SURFACE PRESSURES SOUTH OF
ALASKA AND OCEANIC TEMPERATURE DIPOLES AROUND JAPAN IN THE AUTUMN
AND THE NAO FOR THE ENSUING WINTER. THE SOUTH OF ALASKA SURFACE
PRESSURE AVERAGED LOWER THAN NORMAL AND THE JAPANESE OCEANIC
DIPOLE BOTH CORRELATE TO A NEGATIVE NAO. ON THE OTHER HAND CLIMO
RESEARCH HAS SHOWN ABOUT A 60/40 SWITCH BETWEEN THE NAO STATE IN
OCTOBER AND THE ENSUING WINTER. THE NAO AVERAGED NEGATIVE IN
OCTOBER. LASTLY THE NEWFOUNDLAND WATER POOL TURNED COOLER THAN
NORMAL AFTER HURRICANE BILL PASSED AND HAS NOT LOOKED BACK YET.

IF THE EL NINO REMAINS AS STRONG AS IT HAS BEEN THE PAST TWO WEEKS,
IT CAN OVERWHELM THE NAO AND PDO AND REDUCE ITS INFLUENCE ON OUR
WEATHER. BUT WITHOUT A CERTAIN STRONG EL NINO, THE FATE OF THIS
WINTER WILL BE INFLUENCED SOME BY THESE LESS PREDICTABLE
TELECONNECTIONS. HENCE THIS IN ALL LIKELIHOOD MODERATE EL NINO
WINTER FROM JUST A PDO AND NAO PERSPECTIVE AS OF TODAY LOOKS LIKE
A CROSS BETWEEN THE WINTERS OF 2002-3 AND 2006-7.

THIS FINALLY TAKES US TO THE LIST OF EL NINO AUTUMNS IN THE PAST IN
PHILADELPHIA. ALL OF THESE ANALOG YEARS HAD AN OCTOBER THAT WAS IN
THE AVERAGE OR NORMAL TERCILE OF ALL OCTOBERS DATING BACK TO 1872
AND A NOVEMBER THAT AVERAGED WARMER THAN NORMAL, IN THE HIGHEST
TERCILE.

HERE ARE THE BIG EIGHT OF WHAT OCCURRED WITH PAST EL NINOS THAT HAD
AN AVERAGE OCTOBER AND WARM NOVEMBER. THIS IS BASED ON THE 137 YEARS
OF RECORD IN PHILADELPHIA. THE NORMALS ARE THE CURRENT 1971-2000
NORMALS.


YEAR           ENSUING   ENSUING   ENSUING  AVG    ENSUING ENSUING
               DEC       JAN       FEB      TEMP   PCPN    SNOW

1877-8         40.8      33.0      36.9     36.9    6.41   N/A
1902-3         33.7      32.6      36.5     34.3   14.44   16.8
1930-1         36.6      36.2      37.4     36.7    6.59    4.1
1963-4         27.9      33.0      31.8     30.9    8.51   32.9
1982-3         41.3      34.1      34.0     36.5    8.14   35.9
1994-5         41.9      38.2      31.5     37.2    7.62    9.8
2004-5         37.8      31.8      36.1     35.2   10.23   30.4
2006-7         42.7      38.2      28.0     36.3    7.23   13.4

AVERAGE        37.8      34.6      34.0     35.5    8.65   20.5
NORMAL         37.4      32.3      34.8     34.8    9.57   19.3

THE OFFICIAL CPC OUTLOOK FOR THIS WINTER HAS THE PHILADELPHIA AREA
ON THE BORDER BETWEEN EQUAL CHANCES TO OUR NORTH AND A SLIGHTLY
GREATER CHANCE OF THE WINTER BEING COLDER THAN NORMAL TO OUR SOUTH.
THE PRECIPITATION OUTLOOK HAS EQUAL CHANCES OF BEING EITHER WETTER
OR DRIER THAN NORMAL.

SEASONAL SNOWFALLS HAVE TREMENDOUS VARIABILITY IN EL NINO WINTERS
ONCE THE STRENGTH INCREASES TO MODERATE OR GREATER. THE STRONGER
SUBTROPICAL JET ASSOCIATED WITH THE EL NINO NOT ONLY INCREASES THE
FREQUENCY OF STORMS, BUT ALSO BRINGS IN RELATIVELY WARMER AIR. WE
HAVE WITNESSED IT THIS AUTUMN WITH THREE STRONG NOREASTERS AND
OTHER WEAKER SYSTEMS. THE QUESTION ALWAYS BECOMES HOW COLD WILL IT
BE WHEN THESE STORMS ARRIVE. THE COLDEST AND SNOWIEST EL NINO
WINTERS OCCUR IN PHILADELPHIA WHEN THE EL NINO REMAINS WEAK. IN
PHILADELPHIA SINCE 1950 WEAK EL NINOS HAVE AVERAGED 28.1 INCHES OF
SNOW, MODERATE EL NINOS 22.9 INCHES OF SNOW AND STRONG EL NINOS
16.6 INCHES OF SNOW.

USING A MODERATE EL NINO AS THE BEST ESTIMATE FOR THIS UPCOMING
WINTER AND LOOKING BACK AT MODERATE EL NINOS SINCE 1950, WE FOUND
THAT MODERATE EL NINOS HAVE ACCOUNTED FOR SEVEN OF THE FORTY-SEVEN
SIX INCH OR GREATER MEASURED SNOW EVENTS IN PHILADELPHIA. FROM AN
OVERALL PERSPECTIVE THEY HAVE ACCOUNTED FOR 15 PERCENT OF ALL THESE
EVENTS IN SPITE THAT MODERATE EL NINOS ONLY COMPRISE 10 PERCENT
OF ALL WINTERS SINCE 1950. THE LARGER SNOW EVENTS DURING MODERATE
EL NINO WINTERS FAVOR THE 6 TO 10 INCH RANGE AS MEASURED IN
PHILADELPHIA. SINCE 1950 THERE HAVE BEEN SEVEN EVENTS THAT HAVE
EQUALED OR EXCEEDED SIX INCHES OF SNOW AND ONE THAT HAS EQUALED OR
EXCEEDED TEN INCHES.

THE QUESTION WE WISHED WE KNEW THE ANSWER TO WAS WHETHER THIS
UPCOMING NINO WINTER WOULD BE A ONE HIT WONDER LIKE 1994-5 OR GO
PLATINUM LIKE 1982-3 OR 2004-5. AS ALWAYS PAST PERFORMANCE IS
NOT AN INDICATION OF FUTURE TRENDS. WE HOPE EVERYBODY HAS A VERY
HAPPY AND HEALTHY THANKSGIVING AND UPCOMING HOLIDAY AND WINTER
SEASON. THE SALT HAS BEEN PURCHASED AND THE SNOW THROWER IS GASSED
AND READY TO GO.

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