Winter 2003 - 2004 Preview

Climate Highlight

August 20th, 2003

    The summer of 2003 has seemed very unusually wet.  But has it really been that unusual?  And, if there is precedent of this type of weather, what can we expect for the future?

The purpose of this Climate Highlight is to investigate these two questions.  First, I will examine how abnormal June and July of 2003 have really been and I will search historical records for years that were similar to it in the past.  Then, I want to find out what happened in the months that followed these years with the similar summer.   Hopefully, by finding the similarities in the weather that followed , a pattern will emerge and I can make a forecast for future weather.  In particular, I hope to get a preview of the coming winter with this forecast method.

Analysis of The Summer of 2003

This summer has been remarkably wet. All of the 10 Climate Divisions in Pennsylvania have reported June, July, and early August precipitation amounts that are significantly above normal.  One Climate Division 6 in Northeast Pennsylvania has reported the wettest June and July on record in 2003.

Image 1:  The 10 Pennsylvania Climate Divisions

The following table gives precipitation data for June and July in the 10 Climate Divisions.  For each division, the amount of June, July, June and July combined, and the long-term June and July combined average precipitation is shown.  Also, the historical rank of the precipitation in June and July of 2003 is shown relative to all of the past years that records exist for the divisions (1899 or 1897) .

Table 1:  June and July Precipitation in the 10 Pennsylvania Climate Divisions

These statistics support the qualitative feeling that we all have that it has been extremely wet throughout Pennsylvania this summer season.  The ranking also helps analyze the rainfall pattern over the entire state because it shows which areas have had the most extreme amounts of precipitation relative to the historical record.  The pattern revealed in this data is that it has been especially wet in Northeast Pennsylvania.

Winter 2003 - 2004 Preview

For the 3 climate divisions that had more than 13 inches of rain this past June and July, I looked for other times in history when the weather was extremely wet.  Although this August is not over, in order to get results most similar to 2003, I excluded years  that did not have an abnormally wet August too.  This is because the rainfall totals were exceptional during the first few weeks of August too.  Once I found these similar years, I looked up data about the months that followed.

The next three tables show what happened in the winter that followed the years with extremely wet summers before.  These tables contain both precipitation and temperature data for December, January, February, the monthly averages of the anomalous years, and also the long-term monthly averages.

Table 2:  The Winter That Followed A Wet Summer In Climate Division 1

A composite of these years suggests that December of 2003 may be wetter than normal, January may be drier and colder, and February may be drier in Climate Division 1 if this winter is like the other winters that followed a wet summer.

Table 3:  The Winter That Followed A Wet Summer In Climate Division 2

As for Climate Division 2, when the summer is very wet, December tends to be dry and cold, January cold and wet, and February cold and dry.

Table 4:  The Winter That Followed A Wet Summer In Climate Division 6

The composite of years with a summer similar to this year in Climate Division 6 indicate that December 2003 and February 2004 may be warmer and drier than normal while January may be colder and wetter than normal.

A forecast for the rest of the United State can also be developed from this information.  This is done by plotting the weather for December, January, and February of the years found above to be extremely wet in June and July.  I will use the common years in the climate division data tables above, the years 1903, 1928, 1945, 1975, and 1994, for this analysis.  The two images below represent what, collectively, happened in the winter following other years with extremely wet summers.  The first image is a temperature departure from normal forecast.  The second is a precipitation anomaly forecast.

Image 2:  Forecasted Temperature Departures from Normal in the United States;
 December, January, and February 2003 - 2004

This composite forecast of national temperatures predicts an abnormally cool winter in the eastern portion of the country and an abnormally warm winter in the west.  In particular, the Upper Midwest may be the coldest while the Central Plains are the warmest.  All of the Climate Divisions in Pennsylvania are forecasted to be  colder than normal, although Division 1 may be the most near normal.

Image 3:  Forecasted Precipitation Anomalies in the United States;
December, January, and February 2003 - 2004.

On a national scale, the composite of past similar years to this year indicate that this coming winter may be unusually dry.  In particular, the West, Southwest, and Appalachian Mountain regions could be the most exceptionally dry.  Precipitation for the Northeast, Midwest, most of the South, and Northwest are forecasted to be near normal.  Only Climate Divisions 10 and 6 seem to be predicted to have near normal precipitation amounts in Pennsylvania, the rest are forecasted to be abnormally dry.