Northwest Forecast end of September

Issued September 14, 2011. The forecast models are indicating some changes starting this weekend with chance of moderate precipitation on Sunday (9-18) and there will be changes towards the end of the month.
The map below is for the period 9-21 to 9-27 and is the 500 mb map (for levels 18,000 to 19,000 feet). The map shows the average position of the trough of low pressure which is off the Washington Coast. This type of pattern indicates above average precipitation for the Northwest.