I recall that jalopy came up on the board many moons ago (my goodness, eleven years ago, in fact.). I linked then to a couple of wild speculations but the origin remains as unknown now as it did then.
Blizzard is another unknown (acknowledgments to samclem for offering this in an old thread over at SDMB). Here’s OED:
A modern word, probably more or less onomatopoeic; suggestive words are blow , blast , blister , bluster : the French blesser to wound, has also been conjectured, but there is nothing to indicate a French origin. As applied to a ‘snow-squall,’ the word became general in the American newspapers during the severe winter of 1880–81; but according to the Milwaukee Republican 4 Mar. 1881, it had been so applied in the Northern Vindicator (Estherville, Iowa) between 1860 and 1870. It was apparently in colloquial use in the West much earlier; but whether Col. Crockett’s use of it in 1834 (sense 1) was figurative, taken from the stifling blast, or was the earlier sense, and subseq. transferred to the blast, is not determined.