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Pennsylvania's Precipitation in 2000 and Its Similarities to
Previous Years
By: Paul Dornsife
The purpose of this study is to record Pennsylvania's precipitation for the year 2000 and correlate its totals with previous years. Similarities with any previous years are determined by averaging the precipitation totals for each reporting site within Pennsylvania's ten climate divisions. For a year to be considered similar, four or more months or seasons of previous years must have precipitation totals similar in seven of Pennsylvania's climate divisions. Precipitation totals for each division are graded on a scale ranging from extremely dry to near normal to extremely wet, depending on the percentage of normal precipitation averaged in each of the climate divisions. Similar years and their following years are used as a climatological prediction for 2001 precipitation totals. For example, 1984 was found to be similar to 2000's precipitation totals so 1985 and its precipitation totals for each season will be used as a predictor for 2001's precipitation anomalies. All precipitation forecasts will be done on a seasonal level will breaking Pennsylvania into three regions for simplicity. Zone 1 will include all of the areas to the West of these town to the Ohio border including Pittsburgh and Erie. Zone 2 will be the central third of the commonwealth including with the eastern edge being the cities mentioned previously and the western edge extending from Bradford through Punxatauney through Johnston and Somerset and will include State College Huntingdon, and Altoona. Zone 3 will be the eastern third of the commonwealth extending from a line through Williamsport to Harrisburg, to York and will include the Scranton area. Philadelphia, Reading, Lancaster and, Hazelton. The following table will demonstrate these boundaries:
Table 1: The Zones of Pennsylvania and the Cities and Towns They Include
|
Zone 1 |
Zone 2 |
Zone 3 |
|
Pittsburgh, Erie, New Castle, Washington, Greensburg, Indiana, Warren, Titusville, Franklin |
Bradford, Coudersport, Wellsboro, Lock Haven, Ridgeway, Punxatawney, Clearfield, State College, Huntingdon, Altoona, Johnstown, Bedford, Somerset |
Scranton, Wilkes-Barre, Williamsport, Hazelton, Pocono Mountains, Allentown, Reading, Harrisburg, Lebanon, York, Lancaster, Philadelphia |
Before any similarities can be made, a summary of 2000's seasonal precipitation totals must be discussed. The year began relatively wet with respect to climatological averages. April and June were considerable wet for all of Pennsylvania. Only the southern regions of Zone 2 from State College southward were somewhat dry during this period. July through December was drier than normal for all but the Pocono Mountains and the Upper Susquehanna Valley. The The area of Zone 32 south of State College were the driest averaging 4.5 inches below normal for July through December. Concern about drought conditions are due in this area. Zone 1 and the Lower Susquehanna Valley are slightly dry through the period and drought fears are less in these locales.
Table 2: Seasonal Precipitation Data in 2000 for Pennsylvania's Three Zones
|
|
Winter |
Spring |
Summer |
Autumn |
|
Zone 1 |
Moderately Wet |
Very Wet |
Moderately Dry |
Moderately Dry |
|
Zone 2 |
Moderately Wet |
Near Normal; Moderately Dry South |
Moderately Dry |
Moderately Dry North; Very Dry, South |
|
Zone 3 |
Moderately Wet |
Very Wet |
Moderately Dry |
Moderately Dry South; Near Normal North |
Turning our attention to previous years, two had 4 similar months, 1897 and 1984. Two more had five similar months, 1945 and 1982. 1982 and 1983 will be kept out of this discussion because the 1982-1983 time period had a very strong El Nino anomaly, whereas 2001 is so far a neutral year in the Central Pacific. One month had 6 similar months, including a very wet June and a very dry Autumn, 1916. The climatological forecast will be mainly based upon the events of 1917, the following year. From now on this study will be presented by describing the events of the similar year in a brief paragraph followed by a table with the same format as Table 2.
1897 and 1984: Two Years With Four Similar Months
1897 began similar to 2000 in that two Spring months had above normal precipitation. The second half of 1897 experienced a drier than normal Autumn.
Table 3: Seasonal Precipitation Data in 1898 for Pennsylvania's Three Zones
|
Winter |
Spring |
Summer |
Autumn |
|
|
Zone 1 |
Moderately Wet |
Moderately Dry |
Very Dry June and July; Extremely Wet August |
Very Dry |
|
Zone 2 |
Near Normal |
Moderately Dry |
Very Dry June and July; Extremely Wet August |
Extremely Dry |
|
Zone 3 |
Near Normal |
Near Normal |
Very Dry June and July; Extremely Wet August |
Extremely Dry |
With the exception of August and January, 1898 was a drier than average year for the entire state.
1984 was near normal for the first half of the year. However, the year ended considerably drier for all but the northern part of Zone 3, including the Pocono Mountains and the Upper Susquehanna Valley. The second half of 1984 was strikingly similar to the event of the second half of the year 2000.
Table 4: Seasonal Precipitation Data in 1985 for Pennsylvania's Three Zones
|
Winter |
Spring |
Summer |
Autumn |
|
|
Zone 1 |
Moderately Dry |
Moderately Dry; Very Wet, South |
Near Normal |
Moderately Dry |
|
Zone 2 |
Moderately Dry |
Moderately Dry; Very Wet, South |
Near Normal |
Near Normal |
|
Zone 3 |
Near Normal |
Near Normal; Very Wet, South |
Near Normal |
Near Normal |
1985 turned out to be a year with precipitation totals near normal for all but Zone 1 where a moderately dry Winter, Spring, and Autumn where drier than average conditions prevailed.
1945: The Year With Five Similar Months
January, February, April, October, and December all had similar precipitation totals with respect to the year 2000. This is a good balance of a wet first half of the year concluding with a dry second half of the year. This is very similar to what the year 2000 began and ended.
Table 5: Seasonal Precipitation Data in 1946 for Pennsylvania's Three Zones
|
Winter |
Spring |
Summer |
Autumn |
|
|
Zone 1 |
Very Dry |
Very Wet |
Near Normal |
Very Dry |
|
Zone 2 |
Very Dry |
Very Wet |
Very Wet |
Near Normal |
|
Zone 3 |
Very Dry; South was Near Normal |
Very Wet; South was near Normal |
Very Wet |
Very Dry |
1946 has begun similar to 2001 in that it began with a very dry Winter. 1946 was a year of extremes, with moderately wet conditions in Zone 1, near normal conditions in Zone 2, and very wet in Zone 3.
1916: The Year With Six Similar Months
1916 is the year with the most months that had similar precipitation totals as 2000. 1916 was considerably wet from February through June and trended downward with quite dry conditions in the Summer and Autumn. 19717 would be the best climatological predictor of 2001 precipitation totals.
Table 6: Seasonal Precipitation Data in 1917 for Pennsylvania's Three Zones
|
Winter |
Spring |
Summer |
Autumn |
|
|
Zone 1 |
Near Normal |
Extremely Dry |
Moderately Wet; North was Near Normal |
Near Normal |
|
Zone 2 |
Very Dry |
Extremely Dry |
Moderately Wet |
Moderately Dry |
|
Zone 3 |
Moderately Dry; North was Very Dry |
Extremely Dry |
Moderately Wet |
Near Normal |
1917 was a very dry year that suffered from a fairly strong drought due to a dry Summer and Autumn in 1916 and a a dry Winter and Spring in 1917. If this year is used as a predictor for precipitation totals in 2001, expect a possible severe drought by the Summer.
Using the previous four years as a predictor for 2001's precipitation totals is done by weighting each year differently. Thos yeas with four similar months are not weighted as heavily as the years with five or more similar months. Since the Winter is over and Spring is half way done, emphasis will be place on finding precipitation totals for the rest of the Spring, Summer, and Autumn. Using the method mentioned above, expect a relatively dry year, with the Summer and Autumn being the driest. There is no need to fear a drought though as this is a forecast based on climatology and not actual atmospheric conditions. There is only a slightly higher than normal possibility of drier than normal conditions in 2001 due to previous years which were similar to 2000 and the precipitation totals for the following years.
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