In Moshe's warning to Pharaoh (in Hashem's name) of the fourth plague, arov, he adds (Ex. 8:18-19): וְהִפְלֵיתִי בַיּוֹם הַהוּא אֶת-אֶרֶץ גֹּשֶׁן אֲשֶׁר עַמִּי עֹמֵד עָלֶיהָ לְבִלְתִּי הֱיוֹת-שָׁם ...
The splitting of the Parshiot usually make, at least, some sense. However, in the next two Parshiot the plagues are split up (7 in the first, 3 in the second). Are there sources on why this may be? ...