Start by exporting the data you need from Sentry. Sentry allows you to export data in various formats such as CSV or JSON. Access the Sentry dashboard, navigate to the project you want to export data from, and utilize the export functionality to download the data files to your local system.

Once you've downloaded the data, ensure that it is clean and structured appropriately for Snowflake. This involves checking for any inconsistencies, duplicates, or missing fields. Based on the format of your exported data (CSV, JSON, etc.), you may need to adjust the formatting to match Snowflake’s requirements.

Log in to your Snowflake account and set up the necessary environment for data upload. This includes creating a database and schema if they do not already exist. You can do this using the Snowflake Web Interface or via SQL commands. For instance:
```sql
CREATE DATABASE IF NOT EXISTS sentry_data;
CREATE SCHEMA IF NOT EXISTS sentry_data.public;
```

Define the structure of the table that will store the imported data. Use the `CREATE TABLE` SQL command to specify the table name, columns, and data types. Make sure the table schema matches the structure of your exported data for a seamless import process.

Use Snowflake’s internal stage to prepare for the data load. First, upload your data files to a Snowflake stage. You can use either the Snowflake Web Interface or the SnowSQL command-line tool for this. For example, using SnowSQL:
```bash
snowsql -q "PUT file:///path/to/data.csv @%your_table_name"
```

Execute the `COPY INTO` command to load the data from the stage into your Snowflake table. This command will reference the internal stage where your data is stored and automatically populate the target table.
```sql
COPY INTO your_table_name
FROM @%your_table_name
FILE_FORMAT = (TYPE = 'CSV' FIELD_OPTIONALLY_ENCLOSED_BY='"');
```

After loading the data, perform a series of checks to ensure the migration was successful. This includes querying the Snowflake table to verify the data integrity, checking for any discrepancies, and ensuring all records have been transferred correctly. Use SQL queries to analyze the data:
```sql
SELECT FROM your_table_name LIMIT 10;
```

By following these steps, you can manually move data from Sentry to Snowflake without relying on third-party connectors or integrations.