With the active winter weather pattern, weather amateurs and snow enthusiasts alike will jump on the freely available model sites to find the most outlandish, impractical map, and post it on their social media. This can almost certainly lead to further confusion for the average viewer, who can find it difficult to determine what sources of information are real and which aren’t.
But if weather models are coming up with this data, why shouldn’t we take them at face value?
Snowfall maps produced directly from models are calculated in several different ways. By taking the liquid equivalent (simply put… the amount of ‘rainfall’) and the temperature, the model can plot a snow map. The “ratio” between liquid and snowfall is where the challenge begins. Some of the more common ratios that models use include:
- 10:1 Ratio
- Kuchera Ratio
- Dynamic / Model Ratio
10:1 Ratio represents the equivalent of 1 inch of rain equating to 10 inches of snow. This is a “fixed” rate, but oftentimes is incorrect due to the fact that most snow events will be associated with a lower or higher ratio compared to 10:1.
Kuchera Ratio takes into account the temperatures in the atmosphere in addition to available liquid, coming up with a ratio that usually is closer to reality, although it too can be overdone with totals, especially more than 72 hours out.
The dynamic / model ratio takes into account more short range models and the surface temperatures. While considered the more accurate, this product isn’t always available until 1-2 days before an event.
The final piece to this is mostly experience. Knowing how something will trend: heavier or lighter, west or east, warmer or colder… is what makes the face value of these models so incredibly unreliable when making critical decisions. This is why even with upgrades to AI and new models coming every few years, the “human element” will always be needed.