It's the early modern period. A few Alpine villages, maybe a little town or two, get temporarily cut off from the rest of the world due to heavy snowfall. How can they communicate with the outside? How heavy would the winter have to be for human messengers to no longer be able to travel through mountain passes at all? Would they have homing pigeons, would they even fly in winter, or would longterm storage make them forget their original home? Or is it most likely that they're just cut off until spring and that's it?
Some time ago I saw a documentary showing the winter life in a small village on the Alps between Italy and Austria: even today, with modern means, the houses try as much as possible to be self reliant and avoid to the best they can moving outside when the roads and paths are covered in snow.
When you don't have snow blowers and the like, it would be even more so. Roads blocked = communication blocked, unless you need to communicate something worth risking the life of the person carrying it. And when that person ventures out, they would either use snow shoes or skis.
Unless the places are in line of sight and the weather allows them using beacons like fires, but that would be limited to a set of predefined messages.
I note that the Brenner Pass is the lowest major Alpine pass with a maximum elevation of 1,370 meters or 4,495 feet. The Roman Empire built a road across it, and it has been a main Alpine crossing ever since.
Even before modern times, the Brenner Pass was sometimes open from traffic during the winter. It was crossed by royalty during the winter at least once.
Archduke Maximilian, later Emperor Maximilian II and his wife Archduchess and Princess Maria, and their retinue crossed the Brenner Pass during the winter of 1551-1552. Their retinue included an elephant, Suleiman.
He reached Trent, where the Council of Trent had just finished meeting, on 13 December. He crossed over the Brenner pass to enter Austria, where he was transported along the River Inn and Danube to Vienna. He reached Innsbruck on 6 January for the feast of the Epiphany, and Wasserburg on 24 January 1552. The procession entered Vienna on 6 March 1552.
So since the Brenner Pass was open for travel in December 1551 and January 1552, most Alpine valleys lower than the Brenner Pass would have had fairly light snowfall and roads or paths between farms and villages in a valley would have been fairly easy to travel on. Of course any high passes between valleys could have been higher than the Brenner pass and might have been snowbound when the Brenner Pass was open.
And of course the Brenner Pass could have been closed by snow in most other years, for all that I know.
I note that the 17th century from 1601-1700 was part of the "Little Ice Age" period of colder temperatures.
The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region, that occurred after the Medieval Warm Period. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. The time period has been conventionally defined as extending from the 16th to the 19th centuries, but some experts prefer an alternative timespan from about 1300 to about 1850.
So you might need to look up the current weather and climate of any specific Alpine location you are considering as the setting for your story. And learn how the "Little Ice Age" climate differed from modern climate.
And you might also want to study how Alpine climate changed during different parts of the Little Ice Age. Emperor Maximilian and elephant Suleiman crossed the Brenner Pass in an era considered to be part of the Little Ice Age. So was the Alpine climate even snowier in the 17th century than in 1551-1552?
Juf is a village in the municipality of Avers in the canton of Grisons, Switzerland. At 2,126 metres (6,975 ft) above sea level, it is historically the highest village with permanent residents in Europe, as well as one of its coldest localities. As of 2016, Juf had a population of 31 inhabitants divided between six families in a concentrated settlement. They were 20 in 1991 and 30 in 2001. The first inhabitants were immigrant Walser who arrived in 1292.
Juf differs from settlements in lower valleys in being well above the tree line, the nearest forest being about 5 kilometres away from the village. As a result, the area experiences a cold and wet climate, classified as an alpine tundra climate (ET), with average temperatures far lower than those of La Brévine, traditionally considered the coldest inhabited place in Switzerland. Snowfalls are possible even during summer.
Juf is a lot higher than the Brenner Pas, and there might be a number of other Swiss settlements higher than the Brenner Pass.
La Brévine is a municipality in the canton of Neuchâtel in Switzerland. It is the largest village of the homonymous valley (Vallée de la Brévine), located a few kilometers aways from its largest lake, the Lac des Taillères. The area is particularly renowned for its microclimate and is often much colder than other nearby locations. For its climatic extremes, La Brévine is nicknamed «Siberia of Switzerland». On 12 January 1987, the local weather station recorded a temperature of −41.8 °C (−43.2 °F), the coldest ever recorded in an inhabited location of Switzerland.
La Brevine has an elevation of 1,043 meters or 3,422 feet, lower than the Brenner Pass, but its colder microclimate might make it snowbound even when the Brenner pass is open for travel.
Trepalle is a village (the highest in Italy) in the Italian Alps, a frazione of Livigno, Lombardy. It is considered to be the village located at the highest altitude in Europe (2,069 m or 6,788 ft at the parish church, with the village stretching up to the Passo d'Eira, at 2,209 m or 7,247 ft). Some argue instead that the village of Juf in Switzerland (at 2,126 m or 6,975 ft) is Europe's highest with permanent population, although the same maybe claimed by the Georgian village Ushguli located between 2100 m and 2200 m in Caucasus mountains.
When in the Alps, use an alpenhorn.
The alpenhorn is a 3.5 meter long horn. I'm told that being made out of wood makes it a brass instrument. Wikipedia has an article that displays the lowest note, but I'm not sure how many Hz that is - still, it is obviously a low-pitched sound that will carry a long way. It could communicate from villages to the mountains above - not just to call shepherds, but also to call cows.
Assuming villages are typically on low points near water, I doubt you can use it effectively to communicate between villages separated by tall mountains, but otherwise the sound can be heard over three miles away. If there's anyone on a mountaintop to relay (perhaps a military observation post?) the network should be fairly effective.
Depending on your scenario, you may also want to look further into "infrasound". The odd thing about infrasound is that most people react to it at some level, but only a few of us actually hear it. I don't know what possibilities exist with these or related instruments if you have the right people listening.
Just cut off
In real life, remote mountain villages were completely cut off from the civilization until weather improves (which may happen only in spring). In case of emergency, an experienced mountaineer can risk crossing the path, but this kind of risk needs proper justification.
P.S. After some time I realized that my answer is just a variation of @L.Dutch 's answer. If you agree with my answer, please don't forget to upvote his!
It's actually pretty difficult to be completely cut off. Skis and snowshoes have been around for thousands of years, and were in extensive use in North America and Scandenavia in the "early modern period" (seventeenth and eighteenth centuries). They don't appear to have been used much in the actual historical European Alps, but since this is World Building you could certainly give your village some skis. (Snowshoes are realistically not useful on steep mountains).
Snow on the ground takes an Alpine journey from "difficult" to "very difficult" but not impossible. You wouldn't ski over to the next village for fun, but you would if you needed to. The depth of snow makes no difference to the difficulty - in fact the worst conditions are when there is enough snow to be slippery but enough enough to prevent the skis hitting rocks.
What does cut you off is falling snow. A blizzard makes any mountain journey extremely dangerous, even if you have skis, or frankly even if you have a jeep or a snow cat. You wouldn't do it outside of life or death.
Yodeling for short range communication, and just self sufficient for the rest with no need of long range communication.
Yodeling can be heard a long way away as sound echoes off rocks. I would assume that people knew the best places to do it to communicate with the next mountain or farmstead. Theoretically a message could be passed along like the African talking drums from one place to another several points over. Or even to specialists who would journey down if there was an emergency or someone willing to pay enough.
If you need a reliable source of communication a shuttered semaphore light system or any kind of optical telegraphy might work, as that minimises the risk of avalanche and could in theory be bounced off a glacier surface maintained for the purposes of extending range for example).
There are examples throughout history with mirrors being recorded in use as early as @213 BC by Archimedes during the siege of Syracuse in Sicily, heliographs were used in the battle of Marathon (later renamed to the battle of Snickers! - joke for those of us in the uk of a certain age) in 490 BC.
Advanced usage was also possible in even ancient times with Polybius having a system for numbers to letters so a set number of flashes could be used to represent a letter to spell out words or abbreviations away back between 208–125 BC.
So your options are entirely limited only by what you want to allow, but as for feasible: you would be surprised at how little we have advanced as a species in broad terms, we have some nice new tech, but not so much in the way of fundamental improvements in communication: we simply do the same things faster, with more ease and more often thanks to tech:)
There was a record of communicating from Rome to Capri in seconds/minutes (cant find the exact reference, but found another mention in medium, linked below.
Addendum - after reading your comment, the information above is useful in the negative: as a way to figure out disruptors; if you want total isolation simply add effectors to that end: the harsh winter makes predatory animals be extra aggressive towards anything that moves, just to survive the inclement weather; solitary predators band together to survive (see previous reason); there are other sentiences that are actively preventing communication (other people, or even different others - gods, fae, aliens, elementals etc); weather may behave in a more directly inhibitory manner sometimes (the electromagnetic properties of a storm may lead to a winter-long atmospheric sentience of sorts that is acting to preserve the weather conducive to its own survival, and/or it hates people/enjoys playing "pranks" etc); nature may just win, it is after-all implacable and impersonal, and those two properties alone have managed to beat individuals and civilisations since the dawn of time.
Use Sherlock Holmes' old saying as the justification "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth" (Arthur Conan Doyle): no matter how outlandish and outre the idea may seem, it is possible no matter how improbable (even if you thought it up 5 seconds ago!) :)