Seasonal Forecast
May, June, July 2012
Seasonal Forecast Maps: http://trunc.us/b0239R
Temperature
Precipitation
90-day Outlook summary
A seasonal forecast is the best available prediction of what our climate will be like in the next few months. It is different from a weather forecast in that individual events are not being predicted; rather the average conditions over the next few months are predicted.
As we move into the summer months, there is typically less we can learn from the seasonal forecasts, as forecasting climate in the Southeast has much more skill in the winter/spring months. The current 3-month seasonal forecast (May-Jun-Jul), from the NOAA Climate Prediction Center, shows that warmer conditions should be expected across much of the Southeast. Rainfall is predicted to have equal chances of being above average, normal, and below average during the next 3 months. Presently, there is a transition from La Niña to ENSO-neutral conditions.
How to Read the Seasonal Forecast Maps
A seasonal forecast is often presented by comparing the expected conditions in the coming months to the long-term average conditions during those months (recent 30-year average). Seasonal forecasts are regularly provided as maps with shaded areas indicating the most likely of 3 categories: above average, near average, and below average for seasonal precipitation and temperature.
The 90-day seasonal forecasts of precipitation and temperature are made based on ENSO phase (El Niño, La Niña, Neutral), recent climate trends, and several other factors. The accuracy of these forecasts is generally greater than just using the climate normals (averages from 1981-2010) to forecast climate.
The shaded areas on the maps below show the probability (how likely as a %) that precipitation or temperature is above normal (A), near normal (N), or below normal (B). For each location and month, the coldest (or driest) 10 years from the 30 years of 1981-2010 define the “B” below normal category, the warmest (or wettest) 10 years define the “A” above normal category, and the remaining 10 years define the “N” normal category. Without any forecast, the chance of conditions being in each of the 3 categories is 33.3%. With a forecast, based on ENSO phase and other factors, shading is used to show areas where probability is greater than 33.3%. At any location on the map the probabilities for each of the 3 categories (above normal, near normal, or below normal) adds up to 100%.
An example from the forecast graphics below, consider the 3-month temperature forecast: Looking at southeastern Georgia, shaded the 2nd lightest brown color, means that there is a 50% probability of above average temps. for the 3 months from March to May. The chance of average conditions is almost always fixed at 33.3%, meaning the chance of above average temps for the period is: 100% - 50% - 33.3% = 16.7%.