2 Dollar Technique
Seventy-Five Cent Method
You can hold a pen against the glareshield and sight along the tip to the top of the weather. If the weather moves up the pen you will be in it; if the weather moves down the pen you will be above it.
Method Advantages: You've always got a pen, or something like a pen, handy.
Method Disadvantages: You have to hold the pen and your head steady for a long time, at least a minute. If you move your head the fixed point changes and your results could be wrong.
Two Dollar Method
You can built a sighting edge with two one-dollar bills so that the reference point never changes.
Method Advantages: You can set up with dollar bills to indicate where the top of the weather is and come back to it minutes later for a look at how it is progressing. You don't need to hold anything steady and if you get distracted, you can come back to it.
Method Disadvantages: As a pilot, you may not have two one-dollar bills in your possession. The method does work with Euros, however.
Take two one-dollar bills and fold each in half, lengthwise, and then again so as to form the letter W as viewed edge on.
Place one of the W's on the glareshield parallel to the wings and the other W aligned with your eyes so as to look right down the top of the bill.
Adjust the angle of the siting W so it aligns with the top of the weather. You adjust its elevation angle by moving the other W fore and aft.
A few minutes later, see if the top of the weather is above the W, if so you will be in the weather. If the top of the weather has gone lower, you will clear the weather.
Twenty-Eight Million Dollar Method
For this method to work you will need a HUD. Once you get the HUD, look at the flight path vector. Where it points is where you are going.