1. Right from the get-go, assume that it is in fact God's judgment.
Don't take into account the fact that tornadoes are much more likely in certain parts of the country, particularly the Plains and the Midwest, due to the typical weather patterns in those regions. In fact, leave meteorology and any other science completely out of the discussion. When bad things happen, clearly it is because God is angry at you (or maybe at someone else, but more on that later).
2. Cite Biblical examples to prove your point.
Don't overthink this one. If, as in this case, the disaster involved tornadoes, just look up references to violent wind...or even just wind. That'll be enough. The fact that some or all of these passages are in regards to specific contextual moments that prophets and others were addressing is irrelevant, because even if the cited text includes descriptions of God's judgment on Ephraim, Egypt, or Nineveh, clearly that passage still applies even in the absence of violent or disobedient monarchies that God even warned beforehand. No, these texts are still perfect for average Midwesterners living in an area where this kind of weather comes with the territory.
3. If you can't find an obvious reason why God caused a disaster, imply that there must be some devious underbelly to the affected places that nobody knows about.
Remember, this really is somehow the fault of the people who experienced it, so they must have done something horrible. To address this in your explanation, throw in an allusion to a "dark secret" that some 50-house town in rural Indiana must have been harboring to deserve God's wrath. You don't need to get too specific if there doesn't seem to be a handy obvious sin that you disapprove of present. If the use of innuendo doesn't satisfy you, see point 4.
4. Also state that this was somehow God's judgment on all of us.
Who doesn't need an occasional reminder that God hates us all? Sure, God wiped out some towns, devastated homes, ruined families' lives, and at one point threw an infant from her home after already killing her entire family which caused her to die a slow death lasting a few days, but that might have just been God saying that you or your loved ones could be next. This point has the benefit of being more vague since you don't have to account for whatever specific sins millions of people may be committing. As disappointed as you might be for not being able to name those sins, you'll have to be satisfied with this. Minimize the devastation that just a few hundred or thousand people are now experiencing, stressing that such numbers are small potatoes compared to what God could do to the rest of us.
5. Describe God's judgment with a bit of stifled glee.
Tornadoes and the destruction that they cause aren't exciting enough to be plainly described, especially where God's activity is concerned. So feel free to dress it up a bit by using metaphors like "dragging God's fierce fingers over the earth" and the tornado being a "massive 50-mile lawnmower." You know, sex God's wrath up a bit for the people not immediately dealing with the aftermath, cleaning up debris and mourning loved ones. Those watching on the news need something more vivid to latch onto.
6. Learn absolutely nothing from the book of Job.
When Job loses everything, a few of his friends come over. For the first seven days, they just sit with Job in silence. But after that they got a little antsy and decided that they needed to offer their own explanations for why this happened. That's good, because sitting with the tragedy, offering a mere ministry of presence, and allowing victims space to grieve is just a big waste of time. What you need to do instead is offer an explanation as soon as possible, claim to speak for God, and assume that it's always because somebody somewhere made God angry. Remember to offer such an explanation with as little tact, discretion, pastoral care, or sympathy as possible. Theological correctness always trumps compassion, no matter what.
7. Try to offset your long-winded theological pornography with a one-sentence link to a disaster relief organization.
The bleeding-heart types need to be placated, after all. Besides that, there's clean-up and healing to be done now that God has terrorized people once again in order to prove a point. Also, don't think too hard about the fact that people now have to pick up their lives after God destroyed them. It makes it seem too much like we're more on our own than that God has our best interests in mind. Suggest instead that it's for our own good somehow to have to rebuild entire towns and offer comfort to those affected.
For an example of these tips in action, read John Piper's analysis of the recent tornadoes that swept through the Midwest.