There are two variants of this letter as listed below.
Stormcloak Missive (1)Edit
Though we drove the Emperor's dogs from Fort Neugrad, they still nip at our heels. The chaos in Helgen is bad enough, but now I have word of a new Imperial force assembling in the south, ready to advance on our position as Pale Pass is clear. Send reinforcements, or all our gains will be for naught.
Stormcloak Missive (2)Edit
Fort Snowhawk is a shambles, hardly worth the name. The walls are in ruins, the jail has collapsed, the bailey is half-flooded and swarming with Skeevers. We're patching it up as best we can, but if the Legion attacks, we'll have no better luck defending it than they did. Buy us some time, or we'll lose all the ground we've gained here.