PSL 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:
  1. The ensemble mean 850 mb temp anomaly is calculated by subtracting a 1979-95 climatology from the forecast data at a particular forecast hour.
  2. This is the mean 850 mb temp anomaly which is then plotted.
The 850 mb Temp Normalized Anomalies are calculated as follows:
  1. The ensemble mean is calculated as in step one above.
  2. 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.