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# CDC Map Room Weather Products

**NCEP (NMC) ENSEMBLE FORECAST PRODUCTS**

**FAQ: Frequently Asked Questions**

## Question:

Can you explain the difference between the 850 mb temp mean anomaly and the 850 mb mean normalized anomaly?

## Answer:

The 850 mb Temp Anomalies are calculated as follows:

- The ensemble mean 850 mb temp anomaly is calculated by subtracting a
1979-95 climatology from the forecast data at a particular forecast hour.
- This is the mean 850 mb temp anomaly which is then plotted.

The 850 mb Temp Normalized Anomalies are calculated as follows:
- The ensemble mean is calculated as in step one above.
- The ensemble mean anomaly is then divided by a 1979-95 standard
deviation climatology of the 850 mb temperature. This is the mean
normalized anomaly which is then plotted.

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