In the past 48 hours, over 100 rockets have targeted cities and towns in Southern Israel. The rockets come in the wake of Israel's killing of the head of the Popular Resistance Committee Zuhir al-Qaisi, with intelligence indicating he was planning a major attack on Israel's southern border. Palestinian groups responded to the killing with rocket attacks. In response to these attacks, Israel targeted 15 militants in the Gaza Strip with airstrikes this morning. Tonight's rockets are a response to those airstrikes.
The script, as Haaretz's Amos Harel opines, is well known in this case. The tit-for-tat strikes are likely to calm down in a few days. However, there are two factors in particular which may have an extra calming effect on Israel-Gaza violence.
First, Egypt has been offering to mediate a cease-fire between the sides. The security situation on the Israeli-Egyptian border is a matter of mutual concern for both governments, and only more so as the Egyptian presidential election process begins (with registration of candidates today). Israel is concerned about the long-term stability of that border, and has an interest in mitigating violence there. The original decision to target a senior insurgent in Gaza was likely based on this interest. Israel probably calculated the current response from Gaza, but saw preventing an attack on the border as an event with a far higher cost.
Second, Israel is fresh out of the AIPAC spotlight and has an interest on keeping international and US pressure on Iran. A back and forth between Israel and Palestinian groups in Gaza distracts the global media from the story the Israeli government would prefer to be in the headlines. Israel has an interest in wrapping up this back and forth as soon as possible so it can refocus the agenda on Iran's nuclear program, which it views as the biggest threat to its security.