No. It is nonrecurring income. The court would likely find that a particular source of income included in the calculation of the basic support obligation is not a recurring source of income and then exclude it. You have to show 2 years of income to prove it was a one-time thing.
A wicked ex might argue, but I don't think so. The Financial Declaration form (WPF DRPSCU 01.1550) (http://www.courts.wa.gov/forms/?fa=forms.contribute&formID=13) has a separate section for "Available Assets", which would probably be where you should enumerate the aforementioned IRA.
Seriously, you should probably retain a family law attorney.
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