Using the Ellipse Tool (U), it’s possible to introduce in the picture the falling snow of white color.



The layer’s parameters: Fill 20%



Make a lot of copies of the last made layer and select the Free Transform option to change the elements’ sizes and their placement on the picture.



Using the same instrument, try to make several white patches inside the falling snow.

 



Apply now the Custom Shape Tool (U) to represent several white snowflakes of different sizes.

 



All the snowflakes have the parameter, indicated below: Fill 50%



Write now the inscription, containing the holiday congratulation.

 



The layer’s parameters: Blending Options>Drop Shadow

 



The picture is finished!

View full size here.