March - April 2004 Forecast for Pennsylvania

At the beginning of each month, the Pennsylvania State Climate Office presents an experimental temperature forecast for the Commonwealth. It will be regularly checked with actual data to test its accuracy.

The primary technique employed to produce the predictions below is a mixture of upper air and surface analog methods. The first analog to be analyzed is the anomaly of the February 2004 500 mb flow pattern over North America. The following image shows that the major 500 mb heights anomalies focused on below normal heights in the southwestern regions of the United States and above normal across South-central Canada.

The next step was to find other Februarys with similar 500 mb anomalies using the NCEP reanalysis data set. The following years were the best matches for the geopotential height pattern (images below): 1960 and 1966. These years will be applied in determining the composite deviations in temperature and precipitation.

The second analog applied used to guide in predicting the temperature and precipitation anomalies focused on surface anomalies across the United States. This technique compared years in which regional surface temperature and precipitation deviations from normal were similar to those experienced this past February throughout the climate divisions of the United States. Using these analog years (1895, 1899, 1905, 1929, 1960, 1966, 1978 and 1979) the composite temperature and precipitation trends of the months that followed were calculated.

March 2004

The following two images shows the March composite standardized temperature & precipitation anomalies of the before mentioned years. The first image shows how the average temperature for the month may compare to the average temperature for the Marches of 1895 – 2000. The second image predicts how the precipitation amounts for the coming month may compare to the long-term averages.

The March temperature anomaly map depiction infers it will be cool throughout the Ohio Valley, the Southeast and the Atlantic Seaboard. Warmer than normal conditions would be expected throughout the west, especially Arizona and New Mexico.

The March precipitation anomaly map shows a slightly wetter than normal month across the West. However, the Ohio Valley, especially Southwestern Pennsylvania, and areas surrounding the Mississippi River would experience dry conditions. There is also a possibility of Northern Montana experiencing a drier than normal month.

The following two images shows the April composite standardized temperature & precipitation anomalies of the before mentioned years. The first image shows how the average temperature for the month may compare to the average temperature for the Aprils of 1895 – 2000. The second image predicts how the precipitation amounts for the coming month may compare to the long-term averages.

The April temperature anomaly map suggests that it will be extremely warm throughout the Midwest, Ohio Valley, and Southeastern United States. Cooler than normal conditions are expected to take place across Upper New England and Northwestern United States.

The April precipitation anomaly map shows a drier than normal month throughout much of the nation. Slightly above normal rainfall is possible across regions the Southeastern Coast and Texas.

Using 15-day medium range forecast temperature guidance and the likely monthly departures based on the analog years, the following is a daily temperature forecast for March and April 2004 for western, central and eastern Pennsylvania. This forecast predicts the daily average temperature departure from the 30-year average temperature (dotted maroon line) and the five day running mean (solid line).