What happens if while you are saying the Bracha for lightning you hear thunder and are unable to finish the Bracha in time to begin the Bracha for thunder Toch Kedei Dibur?
If indeed such a thing would happen I think you would lose the opportunity
to say the Bracha on thunder. You could say it on hearing the next thunder
clap.
I think that in the situation you describe one could do as follows. If you
hear the thunder before beginning the Chasimah of the Berachah you could have Kavanah when saying the Chasimah for the thunder as well. If you were
already saying "Oseh" then you have less than 3 words until the end and
will be able to begin the next Beracha Toch Kedei Dibur.
It's good to be prepared for every eventuality.
Ilan Segal
In regards to the answer that you gave, Rabbi Kramer from Yeshiva Chofetz Chaim in Sanhedria Murchevet, Yerushalayim, taught us that the correct way to be yotzei both Berachos is to see the lightning and hear its thunder and then make a Brachah over the thunder (the latter) first (Shekocho Ugvurosoh...) and then on the lightning which you saw before (Oseh Maasey Bireishis.)
(Rabbi Kramer also holds that the Bracha should preferably be said on lightning only when you see the actual lightning bolt.)
Rabbi Kramer held that saying the Brochos in this order avoids any problem you WILL encounter by saying the Bracha over the lightning as soon as you see it - because inevitably you will hear its thunder while making the Bracha over the lightning. The Bracha is made on the thunder first, since you don't pass over an opportunity, since you just heard the thunder - say the Bracha on the thunder now, and then afterwards, say the bracha on its lightning. This solution seems to make the most sense and Bochurim in the Yeshiva have been doing it for awhile.
Yasher Kochachah again on the way you spread Torah throughout the world.
Yaakov Radin
This ruling appears to contradict the ruling of the Mishnah Berurah (227:5) who cites from the MAGEN AVRAHAM that after both seeing lightening and hearing thunder, one only makes one Berachah.
I've noticed that there is a widespread custom to specifically wait until after both seeing lightening and hearing thunder, and then recite two Berachos. I found that the source for this appears to be the ELYAH RABA (cited also in DA'AS TORAH of the Maharsham), who disagrees with the Magen Avraham, and asserts that one should say both Berachos after seeing thunder and lightening. (Even though either Berachah will suffice for both, since he has in mind that one is on the thunder and the other on the lightening, the second is not l'Vatalah). He supports this by pointing out that there are those who hold that one always makes both Berachos on either thunder or lightening (Ra'avad in Shiltei Giborim, Rabeinu Yerucham etc.), and therefore at least in the situation when one hear/sees both of them, he can certainly recite both Berachos.
-Mordecai