Guide To Interpreting Climate Prediction Center Products

Table of Contents

6-10 Day Outlooks

8-14 Day Outlooks

6-10 Day and 8-14 Day Rules

Weeks 3-4 Outlook

Weeks 3-4 Rules

One Month Outlook

Three Month Outlook 

One Month and Three Month Rules

Terciles Visualization

What do CPC products not tell us? 

                   6-10 Day Outlook              

 

Click Here for CPC's 6-10 Day Outlook Interactive Map 

Click Here for the rules when interpreting CPC's 6-10 day outlook

Click Here to go back to the Table of Contents

 

                   8-14 Day Outlook   

 

Click Here for CPC's 8-14 Day Outlook Interactive Map

Click Here for the rules when interpreting CPC's 8-14 day outlook

Click Here to go back to the Table of Contents

 

                  Weeks 3-4 Outlook

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Click Here to go to the Weeks 3-4 Rules

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                  One Month Outlook

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Click Here for CPC's One Month Outlook Interactive Map

Click Here for the rules when interpreting CPC's One Month outlook

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                  Three Month Outlook

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Click Here for CPC's Three Month Outlook Interactive Map

Click Here for the rules when interpreting CPC's Three Month outlook

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6-10 Day and 8-14 Day Rules

Temperature: CPC's 6-10 day and 8-14 day temperature maps show the probability of the observed temperature (the average of the daily mean temperature of all the days in the period) will be in one of three different categories: above normal, near normal and below normal. The daily mean temperature is the 24hr average of all temperature observations for a given station on a given day. The 6-10 Day Average and 8-14 Day Average are the average of all the daily mean temperatures within either the 6-10 day period or 8-14 day period. 

Daily Mean Temperature = Sum of the Temperature Observation Values/Number of Temperature Observations in a 24hr period

6-10 Day Average = Sum of the Daily Mean Temperature Values (Days 6-10)/Number of Days in Period 

8-14 Day Average = Sum of the Daily Mean Temperature Values (Days 8-14)/Number of Days in Period 

These maps show the probability of the 6-10 Day and 8-14 Day Average Temperature being above, near and below the 1991-2020 climate normal for the period.  

Precipitation: CPC 6-10 day and 8-14 day precipitation maps show the probability that the observed precipitation (the total precipitation of all days in the period) will be in one of three different categories: above normal, near normal and below normal.

These maps show the probability of the 6-10 Day and 8-14 Day Total Precipitation being above, near and below the 1991-2020 climate normal for the period.

 

Rules and Examples of Interpreting CPC's 6-10 Day and 8-14 Day Probabilistic Outlooks

1) If the probability of "above" or "below" temperature and/or precipitation is between 33.3% and 63.4%:

- Probability of the opposite category declines by the difference between the higher probability category and 33.3%. 

- Probability of the middle category remains at 33.3%. 

Example 1: CPC's outlook shows a 40% probability of above normal temperatures during the 6-10 day period. 

Probability of Above Normal Temperatures = 40%

Probability of Near Normal Temperatures = 33.3%

Probability of Below Normal Temperatures = 100% - [40% + 33.3%] = 100% - 73.3% = 26.7%

 

2) If the probability of "above" or "below" temperature/precipitation is greater than 63.4%: 

- Probability of the opposite category reaches the minimum allowed value of 3.3% (it does not matter if the favored category is 70%, 80% or 90% as long as it is above 63.4% the opposite category will be 3.3% every time). 

- Probability of the middle category (near normal) decreases by the sum of "above" and "below."

***The probability of the non-favored category is NEVER zero***

Example 2: CPC's outlook shows an 80% chance of below normal precipitation during the 6-10 day period.

Probability of Above Normal Precipitation = 3.3%

Probability of Near Normal Precipitation = 100% - [80% + 3.3%] = 100% - 83.3% = 16.7%

Probability of Below Normal Precipitation = 80%

 

3) If the probability of near normal is greater than 33.3%: 

- Probability of each of the other categories decreases by half of the amount that the middle category exceeds 33.3%. 

Example 3: CPC's outlook shows a 35% chance of near normal temperatures during the 6-10 day period. 

Probability of Near Normal Temperatures = 35%

Probability of Above Normal Temperatures = 35% - 33.3% = 1.7% ---> 1.7%/2 = 0.85% ---> 33.3% - 0.85% = 32.45% (~32.5%)

Probability of Below Normal Temperatures = 35% - 33.3% = 1.7% ---> 1.7%/2 = 0.85% ---> 33.3% - 0.85% = 32.45% (~32.5%)

 

Click Here to go to the 6-10 Day Outlook Maps

Click Here to go to the 8-14 Day Outlook Maps

Click Here to go back to the Table of Contents

 

Weeks 3-4 Rules

Weeks 3-4 is the only category that has no "near normal" category. Weeks 3-4 has above normal, below normal and equal chances categories. 

Since there is no "near normal" category, the rules are more simple here. 

Daily Mean Temperature = Sum of the Temperature Observation Values/Number of Temperature Observations in a 24hr period

Weeks 3-4 Average = Sum of the Daily Mean Temperature Values (Over the Weeks 3-4 Period)/Number of Days in Period 

 

Example 1: CPC's outlook shows a 60% chance of above normal temperatures in Weeks 3-4. 

Probability of Above Normal Temperatures = 60%

Probability of Below Normal Temperatures = 40%

 

Example 2: CPC's outlook shows an 80% chance of below normal precipitation in Weeks 3-4. 

Probability of Above Normal Precipitation = 20%

Probability of Below Normal Precipitation = 80%

 

Example 3: CPC's Outlook shows equal chances of above or below normal temperatures in Weeks 3-4. 

Probability of Above Normal Temperatures = 50%

Probability of Below Normal Temperatures = 50%. 

Click Here to go to the Weeks 3-4 Outlook Maps

Click Here to go back to the Table of Contents

One Month and Three Month Rules

Temperature: CPC's One Month and Three Month temperature maps show the probability of the observed temperature (the average of the daily mean temperature of all the days in the period) will be in one of three different categories: above normal, near normal and below normal. The daily mean temperature is the 24hr average of all temperature observations for a given station on a given day. The One Month Average and Three Month Average are the average of all the daily mean temperatures within either the One Month or Three Month period. 

Daily Mean Temperature = Sum of the Temperature Observation Values/Number of Temperature Observations in a 24hr period

One Month Average = Sum of the Daily Mean Temperature Values (Over a 1-Month Period)/Number of Days in Period 

Three Month Average = Sum of the Daily Mean Temperature Values (Over a 3-Month Period)/Number of Days in Period 

Precipitation: CPC's One Month and Three Month precipitation maps show the probability that the observed precipitation (the total precipitation of all days in the period) will be in one of three different categories: above normal, near normal and below normal.

 

Rules and Examples of Interpreting CPC's One Month and Three Month Probabilistic Outlooks

1) If the probability of "above" or "below" temperature and/or precipitation is between 33.3% and 63.4%:

- Probability of the opposite category declines by the difference between the higher probability category and 33.3%. 

- Probability of the middle category remains at 33.3%. 

Example 1: CPC's outlook shows a 40% probability of above normal temperatures during the One Month period. 

Probability of Above Normal Temperatures = 40%

Probability of Near Normal Temperatures = 33.3%

Probability of Below Normal Temperatures = 100% - [40% + 33.3%] = 100% - 73.3% = 26.7%

 

2) If the probability of "above" or "below" temperature/precipitation is greater than 63.4%: 

- Probability of the opposite category reaches the minimum allowed value of 3.3% (it does not matter if the favored category is 70%, 80% or 90% as long as it is above 63.4% the opposite category will be 3.3% every time). 

- Probability of the middle category (near normal) decreases by the sum of "above" and "below."

***The probability of the non-favored category is NEVER zero***

Example 2: CPC's outlook shows an 80% chance of below normal precipitation during the Three Month period.

Probability of Above Normal Precipitation = 3.3%

Probability of Near Normal Precipitation = 100% - [80% + 3.3%] = 100% - 83.3% = 16.7%

Probability of Below Normal Precipitation = 80%

 

3) If there are equal chances of above, below or near normal temperatures/precipitation: 

- The probability remains at 33.3% for all three categories (above normal, near normal and below normal). 

- Equal chances means that there is an equal chance of the odds tilting in any direction with no single direction being favored. 

Example 4: CPC's outlook shows "equal chances" of above normal, near normal or below normal temperatures during the Three Month period.

Probability of Above Normal Temperatures = 33.3%

Probability of Near Normal Temperatures = 33.3%

Probability of Below Normal Temperatures = 33.3%

 

4) If the probability of near normal is greater than 33.3%: 

- Probability of each of the other categories decreases by half of the amount that the middle category exceeds 33.3%. 

Example 4: CPC's outlook shows a 35% chance of near normal temperatures during the One Month period. 

Probability of Near Normal Temperatures = 35%

Probability of Above Normal Temperatures = 35% - 33.3% = 1.7% ---> 1.7%/2 = 0.85% ---> 33.3% - 0.85% = 32.45% (~32.5%)

Probability of Below Normal Temperatures = 35% - 33.3% = 1.7% ---> 1.7%/2 = 0.85% ---> 33.3% - 0.85% = 32.45% (~32.5%)

***The near-normal category exists for the One Month and Three Month Outlooks. However it is RARELY used at these timescales.***

 

Click Here to go to the One Month Outlook Maps

Click Here to go to the Three Month Outlook Maps

Click Here to go back to the Table of Contents

 

Tercile Examples via Visualization

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are a few things the maps do not tell us: 

1) Does not tell us if the favored category is possible on any given days or weeks in the period. 

2) Does not tell us if the maximum or minimum temperatures lean more strongly into the favored category. 

3) Does not give us the exact probability of any one point on the map. 

4) Does not tell us that particular temperatures will happen or that we can expect those temperatures.

5) Does not tell us anything about the precipitation-type (i.e. snow vs. rain). 

6) Does not tell us that any area will be wetter or drier than any other. 

7) Does not tell us that particular precipitation totals will happen or that we can expect that precipitation. 

***These are probabilistic outlooks which means these products only tell us which way the odds tilt.***

 

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