I heard indirectly about a man who did not recognise the phrase “raw weather.” His wife wondered if it were regional dialect, as they come from different places. Naturally, such questions still make their way to me, because I will care about the answer.
I find no evidence that this is strongly regional. Places that do not have raw days – Santa Fe comes to mind – may have more people who have seldom or never heard the term, but I find examples of usage throughout the US and Canada. I didn’t check the UK and Australia/NZ. However, the SOED records raw, as of weather, chilly and damp; bleak. 16th C. I'd go a little stronger than that, myself. Perhaps that's a NH perspective. That 16th C also suggests it's not going to be especially regional in the US.
It’s rather a sliding scale what constitutes raw weather then, isn’t it? Not only does it vary by region, it varies throughout the year. A raw day in October in NH might be considered an encouraging sign of spring in late February. Part of the sense of rawness, in fact, depends on the weather being unseasonal, a bit unexpected.
Cold is involved of course, plus some wind and moisture. Wind and rain just at the freezing point, too early in the season or lingering too late, would be classic rawness. I suppose one could have cold and wind alone and still get away with the description, but that seeping in of unpleasantness, that invasion up the sleeves or down the neck despite adequate protective clothing must be present. Blown snow would qualify, even if it had fallen earlier. Greyness may not be absolutely necessary, yet…pretty close. But a still day, even with slush or puddle seeping through the shoes, doesn’t quite get the name “raw.”