A bust is a situation in which an anticipated weather event does not occur. This is especially true if there was a high probability of the weather event occurring. Winter weather and severe weather busts are two categories that are anticipated weather events. By anticipated it means that a large percentage of the general public is aware of the threat. Typically when a watch is issued then more people will be aware of the situation. When a warning is issues then even a higher percentage of the general public will be aware of the situation. If the weather changes people’s behaviors then this is another way the weather event is anticipated. Stocking up on groceries before a winter storm is one way of anticipating a winter weather event. This writing looks at some reasons why a winter weather event may bust: 1. Soil moisture is too warm: This situation can occur when the temperature is very close to freezing and the winter weather event requires a ground surface that is at or below freezing. For example, a freezing rain event can be in forecasted but it does not occur since the ground surface is just above freezing. This can result in a cold rain event instead. 2. Not enough lifting to overcome dry air/ Not enough lifting to generate significant precipitation: Another situation that can occur is all the elements being in place for a winter weather event but the lifting is not strong enough. If unanticipated dry air works in aloft or at the surface then lifting will have to be greater to overcome this. What could occur is that some precipitation is generated but evaporates before reaching the ground (called virga). Also, the forecast models could have been overdoing the amount of lifting and this can lead to a bust. 3. Track of low is different from forecast: The track of the low pressure will determine where winter weather occurs in many winter weather situations. If the track is a little too far to the north in the U.S. for example, then it can end up that temperatures are too warm and the winter precipitation ends up being more to the north than the original forecast called for. The best winter weather tends to occur under the low and near the low on the cold side of the air. 4. Forecast is too far out in advance: Forecasts are more likely to be incorrect if the forecast is made too far in advance. There should be caution with forecasts that are made 3 days out or more. The uncertainty is much higher in these longer range forecasts. Forecasts for 1 to 2 days before the event are more likely to occur if based on sound data and judgment. Confidence that a winter weather event will occur is going to the best the day and hours leading up to the event. 5. Weaker than expected accumulation: This is especially true for snow forecasts. In some situations the winter weather will still occur but not to the extent that was forecasted. An example of this is forecasting 8 inches of snow and only 2 occurring. Another example is a forecast of 6 inches of snow, but much of the precipitation falling as rain before finally changing over to snow that accumulates to only an inch. These busts can occur when a slight warming in the temperature profile can result in lower accumulations of snow. |