April Precipitation Outlook

Across the United States, March 2004 will be noted for exceptional warmth across the West and South, wetness over the Great Plains and southern Great Lakes and dry conditions across the Southeastern and Northwestern regions. Other years with similar surface anomalies in March across the country were 1904, 1911, 1916, 1940, 1967 and 1997. With the Marchs of years showing characteristics comparable to the current year, our office looked into what the precipitation anomalies of the April which followed these months. The data used for this study was the monthly divisional precipitation data for Pennsylvania, which is available back through 1899. Each climate division's precipitation departure was calculated and plotted and then analyzed.

After evaluating the data, it was found that for a majority of the months for each climate division, April precipitation trended below normal for these analog years. The notable exception to this is 1940, as all but one climate division experienced at least 1 inch above normal precipitation, with the southeastern and southwestern regions of the state experiencing over 2 inches above normal of rainfall. The other outlier of these six years is 1997, as all climate divisions were exceptionally dry in April.

The overall message of this study proved to be that Aprils following Marchs similar to 2004 were predominantly on the dry side, as even with the 1940 outlier, the average April precipitation departure for the 6 common years ranged from -.2 to -.7 inches across the Commonwealth. However with 5 of the 6 April's experiencing near and below normal precipitation, one could infer that the upcoming April should be on the dry side using this analog forecasting approach.

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Pennsylvania Climate Divisions