Google Ads has launched the a new feature for Smart Bidding that gives you more control over seasonality adjustments. To provide more control in these rare situations, you can now apply seasonality adjustments for Search and Display campaigns, Google said.

Google gave this example, "Let’s say you’re planning a flash sale for the weekend. Historically, you’ve seen a 50% increase in conversion rates when you’ve run a similar sale. With seasonality adjustments, you can apply a predicted conversion rate adjustment and Smart Bidding will consider that adjustment for the date range selected, while trying to hit your target CPA."

Here is how to do it:

Sign into your Google Ads account.

In the top-right corner, click the Tools icon .

From the drop-down menu, select Bid Strategies under "Shared Library".

Under "Bid Strategies", click Advanced Controls.

Select the Seasonality Adjustments option at the top.

To create a new seasonality adjustment, click the blue plus symbol plus .

Give your adjustment a name and description., fill in the event's start and end dates, and choose your scope and devices.

Adjust your conversion rate to reflect your estimated conversion rate change.

Click Save.

Forum discussion at Google Ad Help