Mechanically, the Dresdenverse sunrise is a threshold that sweeps across the world (instead of a creature or spell trying to cross the threshold):
Thresholds can even be conceptual: the transition from night to day has a weakening effect on magic precisely because it is a sort of threshold. (YS230)
Looking at the modes of a threshold (YS230-231), the sunrise acts as a suppressor (reducing effects by a number of shifts equal to the threshold's strength) and as a source of harm (attacking vulnerable creatures with the threshold's strength).
So what is the sunrise's threshold strength? The Dresdenverse sunrise is a powerful symbol of fire's cleansing and purifying qualities, as well as an ancient sign of hope and renewal: the man clutching his pointy stick beside a campfire has survived another night outside the bellies of the prowling beasts.
The sunrise's attack effect is portrayed as universally and automagically destroying ghosts, certain vampire types, and ectoplasmic constructs --up to and often including those with "plot" levels of power. On the other hand, although the suppression effect trashes most unprotected spells it's possible to design spells strong enough to weather a sunrise simply by using shifts to increase duration as normal.
How can we reconcile this apparent dichotomy of strength? The sunrise should qualify as a Catch for most if not all of the creatures it is able to attack; would that be enough to eradicate a summoned demon but let a spell survive a sunrise with just one extra shift? If so, that still leaves the question of its numerical strength. Or does the GM simply rule that the sunrise functions at the power of plot discretion?
If I'm barking up the wrong tree entirely about how the sunrise works mechanically, I'd happily accept an answer telling why and how I should be modeling it differently.