I imagine people who traveled often or had widespread connections—merchants, nobility, and the like—would have known there was a major plague going on. But would the average commoner in a village in Western Europe have known that the disease extended past their local area? Would the have comprehended how widespread it was? How much warning would they likely have had that the plague was spreading before it actually reached them?
News could travel from Rome to London--yes, including across the Alps--in 30 days. So as pestilence spread in Italy, people to the north, east, and west knew it was coming.
Sometimes this was straight-up news. The bishop of Rochester had the delight of spending winter 1348 worried, uh, sick about the coming pestilence, even though it didn't show up in his region for months. But then there's the flip side of news having to travel in the mouths and hands of human messengers--news wasn't the only thing that traveled. As John of Reading wrote:
And there was in those days death without sorrow, marriage without affection, self-imposed penance, want without poverty, and flight without escape. How many who fled from the face of the pestilence were already infected and did not escape the slaughter?
Of course, our surviving written sources come from the elite, not peasants. In this case, the most relevant ones are ecclesiastical. That's because one of the primary frames of reference for understanding pestilence during that first wave was religious. A whole lot of Christians in 1348-1351 believed it was either an apocalyptic show of God's wrath or the apocalyptic show of God's wrath. And a whole lot of that number really, really wanted to turn "the" into "a" by appeasing their Lord.
Ideally, of course, this would be done in advance through prayer, penitence, devotion to saints like Sebastian, parading the Eucharist bread through city streets--in short, things that priests and friars would eagerly do during sermons.
Now, rural peasants did not have the same access to sermons as urban residents, for sure. (In the fifteenth century, we have sources of villagers demanding a full-time priest to staff their local parish church...and then, ten years later, the same villagers demanding a good full-time priest). But peasants weren't self-sustaining pioneers. They generally traveled regularly to multiple larger villages and towns for different markets, if not for Mass. And gossip was the lifeblood of medieval society. What somebody knew, everybody knew.
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For anyone interested in some on-trend distraction:
Best wishes to you all.
I can answer some of this, in part and only for the area of Cologne. My main field of expertise is Cologne‘s Jewish Community before the Pogrom of 1349 (that was at least partially influenced by the approaching plague), so I can answer at least some of the questions. I am certain that there are other perspectives on this and that answers likely differ for other locations, so I‘d love to see answers for other regions or using other sources. I only used some literature that I have available at home (social distancing in effect!) so it is certainly not the full picture, just some impressions from the sources. Usually, I don’t write in English, please excuse my mistakes.
For context, the Black Death arrived in Cologne in December 1349 or later (Schmandt, Judei, p. 88). We know that Cologne‘s council (Rat) knew about the approaching plague in January of 1349 (nearly a year earlier!), when the council answered a letter coming from Strasbourg. The council of Strasbourg had written to Cologne, warning them of the sentiment among the commoners that the Jews were responsible for spreading the plague (Hoeniger, Tod, p. 22f). In their answer, Cologne‘s council state that they don’t believe this to be true. At this point we know that at least the rich, influential citizens of Cologne that were part of the council knew about what they called „the great dying“ („Das grosse Sterben“, Schmandt, Judei, p. 90). Among them were, by the way, many merchants, so I think it is safe to say that some merchants knew about the approaching plague circa one year before it arrived. We can assume that the knowledge was spreading further than this small elite circle, but this is, unfortunately, only speculation.
Around late July/ early August of 1349, there are reports of ‚Flagellants’ in and around the city (Schmandt, Judei, p. 88). Their exact role in the Pogrom that killed most of Cologne’s Jewish citizens in the night from the 23rd to 24th of August 1349 is as unclear as their intentions (comp. Hoeniger, Der Schwarze Tod, p. 14f), but according to Alfred Haverkamp, who extensively studied the sources around the anti-Jewish Pogroms and expulsions that took place during the time in which the plague spread around Europe, these apocalyptic movements were at least partially influenced by fear caused by the approaching plague (Haverkamp, Judenverfolgungen, p. 40-41).
I have to admit that ‚common folk‘ are misrepresented in the contemporary sources, so we have to mostly rely on what the people who wrote these sources reported. Still, only from these few sources we know some things about the knowledge among the population of this area: At least some rich merchants in Cologne knew about the incoming plague around a year before it arrived in the city. Circa four months before the plague reached the area of Cologne, apocalyptic movements formed in the area, maybe influenced by knowledge about the plague. I think it is safe to say that at this point, many people in the area of Cologne likely knew that a plague was spreading. I want to add that Cologne - as, I suppose, many cities at this time - was a regional center and strongly linked to smaller towns and villages in the area (citation needed, unfortunately), so I assume that knowledge was spreading to more remote parts of this region.
I would love if someone that knows more about these ‚Flaggelant’-movements that formed all over Germany (even Europe?) would add to this, I am sure that there is a lot more to say about their knowledge of the plague. Also, I assume many of them might have been commoners.
This answer is explicitly about the knowledge in a large, rich merchant city. I don’t know anything about very remote locations and not much about the ‚common people’ but would love to read more detailed answers!
Sources (in German, sorry):
Haverkamp, Alfred, „Die Judenverfolgungen zur Zeit des Schwarzen Todes im Gesellschaftsgefüge deutscher Städte“, in: Haverkamp, A. (Ed.), Zur Geschichte der Juden im Deutschland des Mittelalters und der Frühen Neuzeit, Stuttgart 1981, p. 223-297.
Hoeniger, Robert, Der Schwarze Tod in Deutschland, Berlin 1882.
Schmandt, Matthias, ‚Judei, Cives et Incole‘: Studien zur jüdischen Geschichte Kölns im Mittelalter, Hannover 2002.