Spring/Summer 2004 Outlook
Applying Analog Techniques Based on Pennsylvania's Ten Wettest Years.
Across Pennsylvania, the 2003 statewide precipitation value of 53.45" was the second wettest since 1895. With this anomalously wet year, we investigated the trends of the years which followed other wet years in the Commonwealth. The top ten wettest years for Pennsylvania from 1895-2003 were found to be: 1942, 1945, 1950, 1972, 1975, 1979, 1990, 1994, 1996 and 2003. However, the Climate Diagnostics Center's Monthly/Seasonal Climate Composites data is only available from Jan 1948 to Dec 2003 leading to the exclusion of 1942 and 1945 for the remainder of the investigation. The next two wettest years, 1956 and 1983, were substituted in their place.
Using these years, composite maps of the 500mb geopotential height were produced by means of the CDC interface for each month of the spring and summer season. The overall trends of these images can then be interpreted as a possible guide to the upcoming upper air patterns across the continental United States.
On the maps themselves, the cold colors represent low heights and warm colors represent high heights. Low heights are associated with a cold column of air which is inducive to troughs. Troughs normally spawn areas of low pressure (rising air), and generally produce relatively cool and disturbed weather. The opposite is true for high heights. High heights are associated with a warm column of air which is inducive to ridges. Ridges are associated with high pressure (sinking air), which usually brings fair and dry conditions.
March composite for ten wettest years. This map indicates an elongated trough encompassing the eastern two-thirds of the country while a ridge is in place in the west.
April composite for the ten wettest years. This map indicates low heights over the northern half of the country and portions of the southwest. There is no evidence of a pronounced ridge across the entire US
May composite for the ten wettest years. This map indicates the northern tier of the US in a trough.
June composite for the ten wettest years. This map indicates ridging in the southwest and extreme northeast part of the country.
July composite for the ten wettest years. This map indicates a ridge in the west and a trough in the east.
August composite for the ten wettest years. This map indicates ridging in the west and north central part of the country.
The composite was made by going to the CDC site at http://www.cdc.noaa.gov/
and choosing the option under Data Access and Plotting: Links to interactive
plotting and analysis pages. Then choosing Monthly/Seasonal Climate Composites
that plots monthly and seasonal composites (averages) variables (mean, anomalies
and long-term means) from the NCEP reanalysis and other datasets.
While on the Monthly/Seasonal Climate Composite page the following changes
were made in order to make a composite:
Variables: Geopotential Height
Analysis Level: 500 mb
Enter Years for composites: Enter the 10 wettest years
1950, 1956, 1972, 1975, 1979, 1983, 1990, 1994, 1996, and 2003
Beginning Month of Season: (Each of the six months were entered one by one to
make a composite for each month)
Example: Beginning Month of Season: March Ending month: March
Plot Type: Anomaly
Map Projection: USA