Is it possible to jam wireless home alarm systems?

A "denial-of-service" wireless attack is very easy. It will disrupt radio communication between sensor and panel. Hopefully, the panel is smart enough to detect that one (or more) of its sensors has failed to report-in. A non-reporting sensor should be assumed under attack. Ask your supplier what protocol is followed if your panel reports that a sensor has failed to report-in.
A much more difficult attack is a "spoof" attack, where the communication between sensor and panel is overpowered by an attacker with a valid message. An "all-OK" signal is very difficult for an attacker to generate because of encryption. Because these signals are regularly sent, it is vulnerable to a determined attacker who is willing to capture signals over a long period.

First of all, to clear some things up: All digital signals are built up by analog signals. As already mentioned in the comments, all wireless communications can be jammed, encrypted or no. And last but not least, jamming is not the same as hacking into. Jamming is just "stopping" the signal.

Now, if the alarm central is good, I would expect it to expect a signal from each and every sensor on a regular basis. If a burglar simply jams one or more of the sensors, the central should realize that it has "lost" a sensor, and sound the bell.

On the other hand, this could lead to false alarms if the reception is bad. This would be a major problem, because over time the user will become annoyed, lose faith in the system, and switch it off. That's not only an expensive paperweight, it's also one that could be stolen.

The first rule of wireless is: Use a wired connection. Don't use wireless unless there is absolutely no other option.

Thus, my advice would be to either get the wired version, or save up for the wired version. But I don't know your house, your other wireless appliances (or your neighbors's), the thickness and materials of your walls, the exact alarm system in question, the warranty, insurance, or clauses in the contract, etc. In the end it's gonna be your decision, so good on you for trying to make it an informed one.

Yes, it is possible to jam wireless alarm systems, probably even with low-cost, low-tech DIY devices (google "broadband jamming DIY"). There are a couple of articles online which report successful attempts, for example this one by Cnet and this one by Forbes. There is also a blog post by a producer of such systems. Both Frontpoint and SimpliSafe, two producers of wireless alarm systems, claim to have proprietary algorithms in place which distinguish between random signal loss due to unrelated interference and an actual attack. (This was a concern I had in a comment to one answer here.) Of course it is impossible to verify these except by performing a comprehensive test.

What I take away from the articles and some other discussions on the net is:

• Yes, it is easy to jam the signal.
• Such attacks are extremely rare, to the point that Frontpoint claims in the blogpost that no successful jamming attack on their systems has ever been reported. Most burglaries are untargeted crimes of opportunity.
• The system may or may not respond properly to jamming attacks.
• Both systems raise an alarm via cell phone which is easy to jam as well, and this time the alarm system can do nothing about it. Of course, cutting the landline is usually easy as well.

tl;dr: Don't worry unless you are a high-profile target.