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THE PROBABILITIES ARE OBTAINED BY RUNNING
THE CURRENT PALMER DROUGHT DATA FOR EACH CLIMATE DIVISION 4 MONTHS AHEAD
USING THE WEATHER SCENARIOS (TEMPERATURE AND PRECIPITATION) OF ALL THE PAST
YEARS SINCE AND INCLUDING 1931. THE PROBABILITY IN PERCENT FOR A GIVEN
CATEGORY IS THE NUMBER OF TIMES THE PROJECTED PDI FELL IN A GIVEN DROUGHT
CATEGORY DIVIDED BY THE NUMBER OF YEARS SINCE 1931 TIMES 100. THE PDI
VALUES FOR THE 7 CATEGORIES ARE:
EXTREME OR SEVERE DROUGHT
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LESS THAN OR EQUAL -3.0
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MODERATE DROUGHT
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GREATER THAN -3.0 AND LESS THAN
OR EQUAL -2.0
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MILD DROUGHT
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GREATER THAN -2.0 AND LESS THAN
OR EQUAL -1.0
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NEAR NORMAL OR INCIPIENT
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GREATER THAN -1.0 AND LESS THAN
CONDITIONS +1.0
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MOIST SPELL
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GREATER THAN OR EQUAL +1.0 AND
LESS THAN +2.0
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UNUSUAL MOIST SPELL
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GREATER THAN OR EQUAL +2.0 AND
LESS THAN +3.0
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VERY OR EXTREME MOIST
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GREATER THAN OR EQUAL +3.0 SPELL
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NOAA/ National Weather Service
National Centers for Environmental Prediction
Climate Prediction Center
5200 Auth Road
Camp Springs, Maryland 20746
September
21, 2005
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