DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS OCT 20 2005

[CaptinCrunch]

PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU OCT 20 2005

NON-TECHNICAL 0.5 MONTH LEAD FORECAST SUMMARY
. . . . . . . .
THE MAIN FACTORS WHICH USUALLY INFLUENCE SEASONAL FORECASTS INCLUDE 1) EL NINO
AND LA NINA – WHICH TOGETHER MAKE UP EL NINO/SOUTHERN OSCILLATION OR ENSO – 2)
TRENDS – 3) TROPICAL 30-60-DAY OSCILLATION- WHICH MAY AFFECT CLIMATE VARIABILITY
WITHIN A SEASON 4) THE NORTH ATLANTIC OSCILLATION OR NAO AND 5) PERSISTENTLY
DRY OR WET SOILS IN THE SUMMER AND SNOW AND ICE COVER IN THE WINTER.

TROPICAL INFLUENCES – INCLUDING ENSO AND TROPICAL 30-60-DAY OSCILLATIONS ARE
CURRENTLY NEUTRAL OR WEAK AND ARE EXPECTED TO HAVE LITTLE OR NO IMPACT ON THE
CLIMATE IN THE NEAR-TERM. TRENDS ARE USED IN THIS FORECAST. THEIR IMPACTS ARE
ESPECIALLY LARGE IN FORECAST LEADS BEYOND 0.5 MONTHS. THE IMPACT OF THE NAO
THIS WINTER IS UNCERTAIN FOR AT LEAST TWO REASONS. FIRST- THE NAO IS CURRENTLY
NEAR ITS NEUTRAL PHASE. ALSO – WE ARE CURRENTLY ABLE TO PREDICT ONLY A SMALL
FRACTION OF THE CLIMATE VARIABILITY ASSOCIATED WITH THE NAO. RESEARCH IS BEING
CONDUCTED WITH THE AIM OF IMPROVING THE USE FOR PREDICTION OF ALL OF THESE
FACTORS.

THE TEMPERATURE OUTLOOK FOR NOVEMBER-DECEMBER-JANUARY (NDJ) 2005-06 CALLS FOR
WARMER-THAN-NORMAL TEMPERATURES ACROSS MUCH OF THE WESTERN UNITED STATES-
INCLUDING ALASKA AND HAWAII. THE GREAT PLAINS - MIDWEST- THE SOUTHERN CALIFORNIA
COAST AND THE EAST COAST HAVE EQUAL CHANCES OF WARMER-THAN... COOLER-THAN OR
NEAR-NORMAL TEMPERATURES THIS WINTER.

THE PRECIPITATION OUTLOOK FOR NDJ CALLS FOR WETTER-THAN-NORMAL CONDITIONS ACROSS
MOST OF ARKANSAS, LOUISIANA AND EASTERN TEXAS. DRIER-THAN-NORMAL CONDITIONS ARE
EXPECTED ACROSS THE SOUTHWEST FROM NEW MEXICO TO SOUTHERN CALIFORNIA.

AS WINTER APPROACHES, NEARLY 20 PERCENT OF THE NATION IS IN SOME LEVEL OF
DROUGHT COMPARED TO AROUND 30 PERCENT OF THE COUNTRY THIS TIME LAST YEAR AS
DEFINED BY THE U.S. DROUGHT MONITOR. FOR THE SIXTH YEAR IN A ROW- DROUGHT
REMAINS A CONCERN FOR PARTS OF THE NORTHWEST AND NORTHERN ROCKIES. WET OR DRY
CONDITIONS DURING THE WINTER TYPICALLY HAVE A SIGNIFICANT IMPACT ON DROUGHT
CONDITIONS. WINTER-SPRING SNOW PACK IS PARTICULARLY IMPORTANT IN THE WEST- AS
MUCH OF THE ANNUAL WATER SUPPLY COMES FROM THE SPRINGTIME SNOW MELT. IT WOULD
TAKE A NUMBER OF SIGNIFICANT WINTER SNOWSTORMS TO END THE CURRENT DROUGHT IN THE
PACIFIC NORTHWEST AND NORTHERN ROCKIES.

BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK

NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE:

http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing

CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS

PACIFIC SSTS ALONG THE EQUATOR WERE GENERALLY NEAR THE LONG-TERM AVERAGE DURING
LATE SEPTEMBER AND THE FIRST HALF OF OCTOBER - WITH THE WARMEST SSTS AND LARGEST
DEPARTURES OBSERVED JUST TO THE WEST OF THE INTERNATIONAL DATE LINE. EQUATORIAL
SUBSURFACE OCEAN TEMPERATURES WERE SLIGHTLY ABOVE AVERAGE IN THE WESTERN PACIFIC
AND 1-2 DEGREES CELSIUS BELOW AVERAGE AT DEPTHS OF 50-100 M BELOW THE SURFACE
BETWEEN 120W AND 95W. ATMOSPHERIC INDICATORS SUCH AS THE LOW LEVEL WINDS AND
CONVECTION IN THE EQUATORIAL PACIFIC REMAIN CLOSE TO AVERAGE AND SUGGEST...
TOGETHER WITH THE OCEAN STATE ... THAT NEUTRAL ENSO CONDITIONS WILL LIKELY
CONTINUE DURING THE NEXT 6-9 MONTHS. AN AREA OF ABOVE AVERAGE SSTS IN THE
SUBTROPICAL ATLANTIC OCEAN AND THE CARIBBEAN SEA...PRESENT FOR MORE THAN A
YEAR...HAS CONTRIBUTED TO ABOVE-AVERAGE TROPICAL CYCLONE ACTIVITY IN THE REGION
AND WETTER-THAN-AVERAGE CONDITIONS OVER PORTIONS OF THE GULF COAST AND EAST
COAST.
. . . . . . . .
PROGNOSTIC DISCUSSION OF SST FORECASTS

THE CONSENSUS OF SEVERAL MODELS USED AT CPC SHOWS SEASONAL MEAN NINO 3.4 SST
ANOMALIES REMAINING VERY CLOSE TO ZERO THROUGH THE WINTER AND THE SPRING. SPREAD
AMONG THE INDIVIDUAL TOOLS HAS DECREASED IN RECENT MONTHS...WITH MORE THAN 80
PERCENT OF THE FORECASTS FALLING IN THE NEUTRAL RANGE...-0.5C TO +0.5C. THUS
THERE IS INCREASED CONFIDENCE THAT SSTS ACROSS THE TROPICAL PACIFIC WILL REMAIN
NEAR AVERAGE THROUGH EARLY 2006.

PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS

THE OUTLOOK FOR NDJ 2005 THROUGH AMJ 2006 IS BASED ON THE MULTI-MODEL ENSEMBLE
FROM IRI... THE CFS... AND STATISTICAL TOOLS... INCLUDING CCA... SMLR AND OCN.
INPUT FROM CDC MODELS - WHICH FAVORS WARM AND DRY CONDITIONS OVER THE WESTERN
TWO-THIRDS OF THE NATION - WAS CONSULTED. ECCA WAS USED FOR NDJ. OCN IS THE
PRIMARY TOOL EXPLICITLY USED FROM MJJ THROUGH NDJ 2006. SINCE THE EXTREME PHASES
OF ENSO ARE NOT EXPECTED TO BE PRESENT...ALL FORECASTS REFLECT INTERDECADAL
TREND MORE THAN ANY OTHER FACTOR. A NEW FORECAST TOOL HAS BEEN DEVELOPED WHICH
COMBINES THE CCA - THE OCN - THE SMLR AND A 15-MEMBER ENSEMBLE MEAN FROM THE CFS
- USING THE KNOWN SKILL OF THE VARIOUS TOOLS TO FORM A WEIGHTED AVERAGE. THIS
TOOL - CALLED CON - HELPS TO REDUCE THE UNCERTAINTY WHICH FORECASTERS CONFRONT
WHEN THEY TRY TO SUBJECTIVELY COMBINE FORECAST TOOLS. CON HAS BEEN USED IN THE
TEMPERATURE AND PRECIPITATION FORECASTS THIS TIME. VERIFICATION OF CON FOR
FORECASTS FROM THE 1995-2005 PERIOD INDICATES THAT IT SHOULD IMPROVE TEMPERATURE
FORECASTS OVER THE CONUS. PRECIPITATION FORECASTS FROM CON HAVE NOT YET BEEN
VERIFIED AND IT IS - THEREFORE - USED MUCH MORE CONSERVATIVELY THAN IT IS FOR
TEMPERATURE.
. . . . . . . .
PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2005 TO NDJ 2006

TEMPERATURE:

THERE ARE ONLY MINOR CHANGES FROM LAST MONTH FOR THE NDJ 2005 FORECAST. THE
PROBABLILITIES FOR ABOVE AVERAGE TEMPERATURES ARE SLIGHTLY REDUCED IN THE AREA OF
THE NORTHERN GREAT PLAINS...WHILE THE AREA COVERAGE FOR THE US AS A WHOLE REMAINS
ABOUT THE SAME. THE REGION OF ABOVE AVERAGE TEMPERATURES IN ALASKA IS UNCHANGED.
THE WEAKENING OF THE PROBABILITIES IN THE NORTHERN GREAT PLAINS IS DUE TO SOME
INDICATIONS FROM MODEL GUIDANCE THAT IT MIGHT NOT BE WARMER THAN AVERAGE...AND
RELATIVELY WEAK TREND INDICATIONS FROM THE STATISTICAL TOOLS. DURING THE WINTER
SEASONS...MODIFICATIONS INCLUDED A REDUCTION IN THE COVERAGE OF ABOVE AVERAGE
TEMPERATURES WEST OF THE MISSISSIPPI DURING DJF AND JFM. THESE CHANGES REFLECT
THE CONTINUED UNCERTAINTY WITH THE POTENTIAL PHASE OF THE NAO DURING THE WINTER
AS WELL AS CONFLICTS BETWEEN OCN - WHICH FAVORS ABOVE AVERAGE TEMPERATURES IN THE
MIDWEST - AND INPUT FROM THE IRI - WHICH FAVORS AVERAGE TO BELOW AVERAGE IN THAT
REGION.

. . . . . . . .
PRECIPITATION:

CHANGES FROM LAST MONTHS FORECASTS ARE LESS EXTENSIVE FOR PRECIPITATION THAN THEY
WERE FOR TEMPERATURE. FOR NDJ - THE FORECAST IS NEARLY IDENTICAL TO THAT ISSUED
LAST MONTH. HOWEVER...THE TOOLS ARE NOT ALL THAT IMPRESSIVE IN SUPPORTING
EITHER THE DRIER THAN AVERAGE CONDITIONS INDICATED FOR THE SOUTHWEST OR THE
WETTER THAN AVERAGE CONDITIONS INDICATED FOR THE ARKLATEX REGION. SUPPORT FOR
DRYNESS IN THE SOUTHWEST COMES MAINLY FROM THE ECCA - WHILE WETNESS IN THE
ARKLATEX REGION IS SUPPORTED BY CON BUT NOT BY ECCA. THE IRI TOOL WEAKLY
SUPPORTS DRYNESS THROUGHOUT MUCH OF THE US EAST OF THE ROCKIES. THE AREA OF
BELOW AVERAGE PRECIPITATION IN THE SOUTHWEST IS DROPPED IN THE FORECASTS FOR DJF
2005-2006 DUE TO INCONSISTENCIES BETWEEN THE CON (WET) AND THE IRI (DRY). IT IS
INTERESTING TO NOTE THAT THE CON INDICATES SMALL AREAS OF WETTER-THAN-AVERAGE
CONDITIONS TO THE LEE OF THE GREAT LAKES DURING NDJ AND DJF...IMPLYING ENHANCED
LAKE EFFECT PRECIPITATION. THIS IS NOT INCLUDED IN THE OFFICIAL OUTLOOK...BUT IT
IS SOMETHING THAT SEEMS PLAUSIBLE BASED ON THE VERY WARM LAKE TEMPERATURES
(GREATER THAN 2C ABOVE AVERAGE)AND SOME OF THE MODEL GUIDANCE WHICH INDICATES AN
ANOMALOUS TROUGH ALONG THE NORTHEAST COAST.

NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL
(CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).