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

LESS THAN OR EQUAL -3.0

MODERATE DROUGHT

GREATER THAN -3.0 AND LESS THAN OR EQUAL -2.0

MILD DROUGHT

GREATER THAN -2.0 AND LESS THAN OR EQUAL -1.0

NEAR NORMAL OR INCIPIENT

GREATER THAN -1.0 AND LESS THAN CONDITIONS +1.0

MOIST SPELL

GREATER THAN OR EQUAL +1.0 AND LESS THAN +2.0

UNUSUAL MOIST SPELL

GREATER THAN OR EQUAL +2.0 AND LESS THAN +3.0

VERY OR EXTREME MOIST

GREATER THAN OR EQUAL +3.0 SPELL

 NOAA/ National Weather Service
National Centers for Environmental Prediction
Climate Prediction Center
5200
Auth Road
Camp Springs, Maryland 20746

September 21, 2005