Median date of first event

June 30

May 3G

June 3

July 3


June 24

Average date of first event

July 22

July 1G

July 1e

June 28

July 27


Note: NS = nonsignificant result, in RAINMAN a result with probability less than 90 percent.

the "SOI negative" scenario. Values in this column indicate a higher than average chance (53 percent) of the first rain event in the coming season occurring by June 1.


1. A farmer at Cobar, New South Wales, wishes to reduce water losses from his farm's water reservoir through a new technique. He is looking for information on the likely period during which weekly evapora tion may exceed 70 mm in the coming summer. He also wants information on approximate dates by which the first event is likely to occur in the season.

The information required by the farmer at Cobar is easily generated with MetAccess. Information about MetAccess can be obtained at <http://www.>. MetAccess (Serial# 2001, Version Sept99) has historical records for Cobar.

Procedure. Open Cobar from MetAccess Weather Files; choose "Outputs" from the menu bar and "Probability" from the dropdown window. The "Probability" dialogue box opens. Select:

Evaporation greater than 70 mm in a seven-day interval


Period from September 1 to March 31


A graph (Figure 8.1) is generated (can be a table also) which shows during the period November 24 to February 16 more than 50 percent chance of weekly evaporation exceeding 70 mm.

90.0 80.0 70.0 60.0 g 50.0 ® 40.0 30.0 20.0 10.0 0.0

Sep 1 Oct 13 Nov 24 Jan 5 Feb 16


FIGURE 8.1. Probability of total evaporation greater than 70 mm over seven days at Cobar

Cobar Mo (1971-1998)

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