Begin by ensuring that AWS CloudTrail is enabled in your AWS account. Navigate to the CloudTrail console and create a trail if one doesn't exist. Configure the trail to log events to an S3 bucket. This bucket will serve as the storage location for CloudTrail logs.

Use AWS Identity and Access Management (IAM) to create a user or role with the necessary permissions to access the S3 bucket. Attach policies like `AmazonS3ReadOnlyAccess` to this user or role. Generate access keys if creating a user, and note these credentials as they'll be needed later.

Download and install SnowSQL, Snowflake's command-line interface, on your local machine or a server. Configure it with the necessary connection details for your Snowflake account, including your account name, user, warehouse, database, and schema. Use the `snowsql -a -u ` command to set up the connection.

In Snowflake, create an external stage that points to the S3 bucket containing CloudTrail logs. Use the following SQL command in SnowSQL:
```sql
CREATE STAGE my_s3_stage
STORAGE_INTEGRATION = (your_storage_integration)
URL = 's3://your-cloudtrail-bucket-name/'
FILE_FORMAT = (TYPE = 'JSON');
```
Ensure your Snowflake account has the necessary access to the S3 bucket through a storage integration.

Create a target table in Snowflake where you want to load the CloudTrail data. Use the `COPY INTO` command to load data from the S3 stage into this table:
```sql
CREATE OR REPLACE TABLE cloudtrail_logs (
event_id STRING,
event_time TIMESTAMP,
event_name STRING,
user_identity STRING,
aws_region STRING,
source_ip_address STRING,
user_agent STRING,
-- Add other fields as needed
);

COPY INTO cloudtrail_logs
FROM @my_s3_stage
FILE_FORMAT = (TYPE = 'JSON')
PATTERN = '.*your-log-file-pattern.*';
```

To keep your CloudTrail logs in Snowflake updated, automate the data loading process. Use AWS Lambda or a cron job on an EC2 instance to periodically trigger the `COPY INTO` operation. Use the Snowflake REST API or a script that utilizes SnowSQL for this task.

Regularly check the Snowflake table to ensure data is being loaded correctly. Use Snowflake's query capabilities to validate the integrity and completeness of the data. Set up alerts or dashboards in Snowflake for monitoring purposes, ensuring any discrepancies or issues are quickly identified and addressed.

By following these steps, you can efficiently transfer your AWS CloudTrail data to the Snowflake Data Cloud without relying on third-party tools.