Lol, just look at the names of the months.
Morning Star
Sun's Dawn
First Seed
Rain's Hand
Second Seed
Midyear
Sun's Height
Last Seed
Hearthfire
Frostfall
Sun's Dusk
Evening Star
I'm no lore junkie, so this may be wholly wrong, but; From what I gathered from the various books and whatnot, the seasonal shifts on Nirn are very mild, which would indicate the planet has little to no wobble on it's axis and a very regular orbital path around the sun. Additionally, the Moons don't change location in their paths, which would also support this.
So seasons would be different by a matter of small degrees, rather than Earth, which has dramatic seasonal shifts varying by latitude. In Nebraska for example, summer is 100+ with 90+ humidity,while winter is below freezing with blizzards. Where I grew up in California however, the seasons were marked only by a slight temperature difference and more rain. Christmas stuff in stores? Must be winter, etc.