Regional Verification of CPC’sSeasonal Outlooks

Michael Halpert

&

Kenneth Pelman

Climate Prediction Center

Seasonal Outlook Schedule/Leads

• Each month, near mid-month CPC prepares a set of 13 outlooks for 3-month “seasons” (any set of 3 adjacent months) for lead times ranging from ½ month, 1 ½ months, 2 ½ months, 3 ½ months, …, 12 ½ months.

• The outlook for each successive/prior lead time overlaps the prior/successive one by 2 months. This overlap makes for a smooth variation from one map to the next.

Outlook Categories and Probabilities

Seasonal outlooks are prepared for average temperature and total accumulated precipitation category

Three categories are used (terciles). These are BELOW-,NEAR- and ABOVE-normal (median), for temperature (precipitation).

Regions where the likelihoods of the three categories are the same (33.33…% each) are designated as “EC”, for equal chances.

In non-EC regions the labels on the contours give the total probability of the dominant category.

Verification

• Heidke Skill Score

• H=[ ( NC – CH)/(NT – CH) ] * 100

• H=Heidke Skill Score• NC = total number of correct forecasts by station• NT = total number of forecasts made by station• CH = number of correct forecasts, by chance

• In 3 class system, scores range from -50 to +100

• Examples

• a. 99 stations, 50 correct forecasts

• H = [(50-33)/(99-33)] *100 = 25.8

• b. 51 stations, 12 correct

• H = [(12-17)/(51-17)]*100 = -14.7

• c. 45 stations, 35 correct

• H=[(35-15)/(45-15)*100 = 66.7

Verification

0.5 Month Lead Skill

Data

9+ years of seasonal forecastsJFM 1995 – AMJ 2004

112 Total Forecasts

Winter: NDJ – JFM (28)Spring: FMA – AMJ (30)Summer: MJJ – JAS (27)Fall: ASO – OND (27)

Temperature – All Seasons

Temperature – By SeasonWinter Spring

Summer Fall

Temperature – By Category (All)

Above Below

Temperature - Category DJF&MAM

Winter/Above Winter/Below

Spring/Above Spring/Below

Temperature - Category JJA&SON

Summer/Above Summer/Below

Fall/Above Fall/Below

Temperature Summary (Official)

• Good skill from the Pacific NW, peaking in the SW and extending through the South.

• No skill in N. Plains, Great Lakes, NE

• Winter forecasts best, Fall poorest

• No skill in NE, always skill in SW

• All skill comes from above normal; negative skill everywhere for below

Forecast Tools

1. Optimal Climate Normal (OCN)

2. Canoncial Correlation Analysis (CCA)

3. Coupled Model (CMP)

4. Screened Multiple Linear Regression (SMLR)

Temperature – OCN/CCA All

OCN CCA

Temperature – OCN/CCA By Category

OCN/Above OCN/Below

CCA/Above CCA/Below

Temperature – SMLR/CMP All

SMLRCMP

Temperature – SMLR/CMP By Category

SMLR/Above SMLR/Below

CMP/Above CMP/Below

Forecast Tools - DJF

OCN CCA

CMP SMT

Forecast Tools - MAM

OCN CCA

CMP SMT

Forecast Tools - JJA

OCN CCA

CMP SMT

Forecast Tools - SON

OCN CCA

CMP SMT

Precipitation – All Seasons

Precipitation – By Season

Winter Spring

Summer Fall

Precipitation – By Category (All)

Above Below

Precipitation - Category DJF&MAM

Winter/Above Winter/Below

Spring/Above Spring/Below

Precipitation - Category JJA&SON

Summer/Above Summer/Below

Fall/Above Fall/Below

Precipitation Summary (Official)

• Skill in West, South and NE (few cases)

• Skillful regions vary by season

• Skill in all seasons in NW, except Spring

• Skillful forecasts for both above and below in the SW and along Gulf Coast, FL

• Skill for winter/spring forecasts for below in South, only along Gulf Coast for above

Precipitation – OCN/CCA All

OCN CCA

Precipitation – OCN/CCA By Category

OCN/Above OCN/Below

CCA/Above CCA/Below

Precipitation – SMLR/CMP All

SMLRCMP

Precipitation – SMLR/CMP By Category

CMP/Above CMP/Below

SMLR/Above SMLR/Below

Forecast Tools - DJF

OCN CCA

CMP SMT

Forecast Tools - MAMOCN CCA

CMP SMT

Forecast Tools - JJA

OCN CCA

CMP SMT

Forecast Tools - SON

OCN CCA

CMP SMT

DJF 2004-2005 Outlook