weatheres

cypriusgray  asked:

How do thunder snows happen?

Thundersnow is pretty cool since we don’t see it often. 

So for anyone unfamiliar, thundersnow is basically lightning that occurs during a snowstorm. In concept it sounds pretty boring, but really there’s only about 6.3 snow events with lightning on average each year nationwide.  

Being so rare, it’s just the sort of thing that makes Jim Cantore more excited than a three year old on Christmas


Lets first breakdown the dynamics of a typical storm that has lightning - so no snow necessary as of yet. Lightning happens after the storm has gained a charge as a result of particles rubbing and colliding against each other in the strong vertical convection greater than 5m/s. The clouds that make up these storms are massive in height, as high as 50,000 feet or more. All of this results in an updraft of moist air from the surface. 

This is a massive contrast to a snowstorm. Snowstorms usually have fairly gentle vertical convection when compared to a summer thunderstorm. Additionally, they’re a lot more shallow in the atmosphere, about 20,000 feet in height usually. The surface being around or below freezing temperatures just doesn’t allow for a massive amount of moisture content and instability. So how do we get the sort of atmospheric movement to match up to a summer thunderstorm? We need strong forcing mechanisms! 

Often if we observe thundersnow we see rather strong conditions working in combination with each other. This can include things like lifting from frontal activity, lake-effect snows, orographic lifting, or even synoptic forcing underneath the trowal in strong occluding mid-latitude cyclones. There’s a number of other mechanisms that play into strong winter storms that can create lightning but these are a few of the culprits we can often point to. 

See trowal


We’ve basically established that thundersnow is most often observed in the most elite of winter storms - blizzards with snowfall rates of 2-4 inches per hour. Interestingly enough, that snowfall decreases your visibility to ¼ a mile and dampens the sound of thunder to a 2-3 mile radius (normal thunderstorms can be heard from much larger distances), so even if you’re in a storm that has thundersnow, you may never notice! 

As an aside, there appears to be evidence that tall buildings and communication towers may reduce the thresholds needed for positive cloud-to-ground lightning in winter storms (see 5.3)

Feel free to ask if you have more questions! 

As long as you have a single iota of social grace, a quick conversation about the food at your holiday gathering should be completely safe. “Wow, this ham is amazing,” was always a great way to fill dead air, and also to test who was sober enough to realize there wasn’t a ham. “Did everyone notice how much weight Uncle Mark has gained?” was also a great subtopic in this category, to both make people feel better about themselves and see if your nephews have the basic social aptitude to know they have no Uncle Mark.

Your dad and aunt arguing about GMOs, even though neither of them can remember what “GMO” stands for.

What was once a boring, safe topic is now a minefield because the developed world is currently in a food civil war. On one side are people who think that eating anything that wasn’t lovingly grown by yoga instructors is tantamount to poisoning yourself with bubonic rat semen. On the other side are people who think that Roundup weed killer should be a standard condiment, like ketchup or insulin.

5 Topics That Used To Be Small Talk (And Start Fights Now)