Hi there! I understand your FloodWatch app opens for just a split second and then closes right away on your Mac running OS X 10.15.7. Let's get to the bottom of this.

First, could you tell me if this started happening recently or after any changes, like an OS update or app reinstall? Also, have you tried any troubleshooting so far, such as restarting your computer or reinstalling the app?

Meanwhile, here’s a step-by-step approach we can try:

1. Restart Your Mac: Sometimes a simple restart resolves temporary glitches.

2. Update the App: Check the App Store for any available updates to FloodWatch. Running the latest version ensures compatibility.

3. Check for OS Updates: Although you’re on 10.15.7, verify if any system updates are pending. Some apps rely on system files that, if outdated, can cause crashes.

4. Clear App Cache/Data: On Mac, app preferences or cache files can sometimes cause crashes. To reset FloodWatch preferences:
- Open Finder.
- In the menu bar, click “Go” > “Go to Folder…”
- Type ~/Library/Containers/ and press Enter.
- Look for a folder named like the FloodWatch app (e.g., com.floodwatch.app).
- You can move this folder to the Desktop to back it up temporarily.
- Restart the FloodWatch app and see if it opens normally.

5. Check Console Logs: If you’re comfortable, you can open the Console app (found in Applications > Utilities) and filter for FloodWatch-related error messages during the app crash. This info can help identify the cause or confirm if it’s a known issue.

If these don’t help, sometimes reinstalling the app after completely removing associated files can work:
- Delete the FloodWatch app.
- Repeat the cache/preferences cleanup mentioned above.
- Restart your Mac.
- Download and install FloodWatch fresh from the App Store.

Let me know how these steps go or if any of them you’ve already attempted. I’m here to help you get it running smoothly! Are you able to try these now?