December 2003 / January 2004 Experimental Forecast for Pennsylvania

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

For verification of the December 2003 / January 2004 forecast, visit the Verification Page.

November 2003 Conditions

The primary technique employed to produce the predictions below is an analog method. First, we determined the 500 mb flow pattern of the previous month by graphing the departure from normal.

Next, we compared the 500mb anomalies in November 2003 with previous November flow patterns using the NCEP reanalysis data set. We found that the November 1948, 1973, and 1985 were the most similar to this past November's geopotential height pattern (images below).

Predictions

The following products to guide in predicting the temperature and precipitation anomalies for December 2003 and January 2004 applied a second analog approach. This method compared years in which regional surface temperature and precipitation deviations from normal were similar to those experienced this past November throughout the United States. Using these years (1921, 1927, 1942, 1945, 1948, 1952, 1973, and 1985) the composite temperature and precipitation trends of the Novembers and Decembers that followed were calculated. 

December 2003

The following two images show the analog forecast for December 2003.  The first image predicts how the average temperature for the month may compare to the average temperature for the Decembers of 1895 – 2000.  The second image predicts how the precipitation amounts for the coming month may compare to the long-term average amount.

The December temperature anomaly map predicts that it will be cooler than normal along the Pacific and Atlantic Coasts, Ohio Valley, and Tennessee. Cold conditions are expected throughout the Northwest, Central Plains, and northern Rocky Mountains.  Warmer than normal conditions are expected in the Southwest, Maine, and Nevada.

The December precipitation anomaly map predicts a drier than normal month throughout Louisiana, Mississippi, New Mexico, Western Oregon, Western Tennesee, and Texas. The rest of the country, especially along the Atlantic Coast and Wisconsin, and Northern California, have wetter than normal December forecast.

January 2004

The following two images show the analog forecast for January 2004.  The first image predicts how the average temperature for the month may compare to the average temperature for the month in 1895 – 2000.  The second image predicts how the precipitation amounts for the month may compare to the long-term average amount.

The temperature anomaly map predicts that this January will have significantly above average temperatures in the eastern portion of the country, while the western portion is slightly cool or near normal.

The precipitation anomaly map predicts drier than normal conditions from Lake Ontario down the Ohio River, along Gulf Coast, southern Atlantic Coast, and in Northern California. Near normal precipitaiton is expected throughout the rest of the country.

Pennsylvania Forecast

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 December and January in western, central and eastern Pennsylvania.  This forecast predicts the daily average temperature departure from the 30-year average temperature.