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Table 7. Summary of single season Dec.-Mar. Precipitation/HCI Relationships for the Arkansas <br />basin (‘X’ indicates a relatively strong relationship and ’O’ indicates a relatively weak relationship). <br />PDOMEISOINino 3.4 NAOAMO <br />Upper Ark. <br />OO <br />Middle Ark. X <br />Lower Ark. XX <br />O <br />B - April-June Precipitation (single season) <br />Upper Arkansas: <br />During this period the PDO relationships earlier noted do experience a notable <br />reversal as spring approaches. The negative correlations between the PDO values and <br />precipitation tend to reverse with the three-month averages by the end of April, indicating <br />that what regime is important in one part of the year may be different in another period of <br />the year. Also a curious but, sharper reversal of the relationships between the ENSO <br />phase and precipitation takes place with El Niño’s tendency to have higher precipitation <br />values and vice versa regarding La Nina. <br />Middle Arkansas: <br />During this period the PDO relationships noted do experience a notable reversal <br />as spring approaches. The negative correlations between PDO and precipitation values <br />tend to reverse with the three-month averages by the end of April, indicating that what is <br />regime is important in one period of the year may be different in another period of the <br />year. Also a curious but, sharper reversal of the relationships between the ENSO phase <br />and precipitation takes place with El Niño’s tendency to have higher precipitation values <br />and vice versa regarding La Nina. <br />Lower Arkansas: <br />The modest trends of higher precipitation values in La Nina and drier El Nino <br />regimes continued in this region through this period and are fairly steady as spring <br />approaches. However, a curious relationship occurs with the NAO as the relatively <br />strong positive relationship between precipitation and NAO values quickly reverses from <br />early winter to late winter. (i.e. late-fall/early winter positive values of NAO would <br />generally portend greater precipitation values and vice versa however, as April <br />approaches it would be more favorable to have negative NAO values for greater <br />precipitation, ect.). <br />29 <br />