When Do Rains in Israel Start Becoming a Bad Sign?

Based on this article which lists the sources and summarizes them in the סיכום (summary), I created the following chart (all errors are mine and I welcome corrections):

Source		End of Fasts for Rain	Effective Start of Siman Kelala	Siman Kelala Even If It Rained in the Winter?
Bavli		End of Lunar Nissan	Rosh Hodesh Iyar	Yes
Yerushalmi	Tur (acc. to Lehem Mishneh)	End of Tekufat Nissan	Late June-Early July	No
	Tur (acc. to Bah)	30+ Days from Start of Tekufat Nissan (acc. to Shemuel)	May 6-7
	Variation of Above	30+ Days from Start of Tekufat Nissan (acc. to Rav Adda)	April 26-27
	Rambam and Shulhan Aruch	Approximately 30 Days from Equinox	April 19-20

I'm not sure if the horrific tragedy that occurred in Israel today (April 26th) qualifies.  May the families of those who lost their lives be comforted among the mourners of Zion and Jerusalem.