Display screen or portion thereof with a transitional graphical user interface

The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is a front view of a display screen with a transitional graphical user interface showing a first image in a sequence in color; and,

FIG. 2 is a front view showing a second image in the sequence in color.

The longer-incremented broken lines show a display screen portion to illustrate environment and form no part of the claimed design. The dash-dot-dash broken lines of certain features define boundaries for those features and form no part of the claimed design. The finer-incremented broken lines in the remainder of the graphical user interface form no part of the claimed design.

The grayscale in the drawings indicates a contrast of appearance.

The subject matter in this patent includes a process or period in which an image changes into another image. The process or period in which an image transitions to another image forms no part of the claimed design.