Pennsylvania Water Science Center
Precipitation is monitored in terms of departures (surpluses or deficits) from 30-year normal monthly precipitation quantities. Precipitation data for each of the 67 counties is available from the National Weather Service.
Drought conditions result from precipitation deficits. However, a single-month precipitation deficit does not indicate a drought. Rather, droughts result from accumulations of precipitation deficits over periods of three or more months. The table below provides the percentages of cumulative deficits, for periods ranging from 3 to 12 months, which are indicative of the various drought stages in accordance with Pennsylvania's drought monitoring criteria.
Precipitation Drought Monitoring Criteria
 |
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|
Duration of Deficit Accumulation (months)
|
Drought Watch (deficit as % of normal precipitation)
|
Drought Warning (deficit as % of normal precipitation)
|
Drought Emergency (deficit as % of normal precipitation)
|
|---|---|---|---|
|
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|
3
|
25.0
|
35.0
|
45.0
|
|
4
|
20.0
|
30.0
|
40.0
|
|
5
|
20.0
|
30.0
|
40.0
|
|
6
|
20.0
|
30.0
|
40.0
|
|
7
|
18.5
|
28.5
|
38.5
|
|
8
|
17.5
|
27.5
|
37.5
|
|
9
|
16.5
|
26.5
|
36.5
|
|
10
|
15.0
|
25.0
|
35.0
|
|
11
|
15.0
|
25.0
|
35.0
|
|
12
|
15.0
|
25.0
|
35.0
|
|
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U.S. Department of the Interior |
U.S. Geological Survey
URL: http://pa.water.usgs.gov/monitor/precip/explanation.html
Page Contact Information: Pennsylvania WSC Webmaster
Page Last Modified: Monday, 06-Aug-2007 15:28:43 EDT
