Martinsville Weather - Winter Storm Forecast Review for Sat 01/19/08
Instead of doing a typical forecast review, I wanted to do something a little different this time, and give you an explanation of all the factors involved in predicting this particular system and why this forecast was so difficult.
Pattern Overview: We were dealing with two primary factors that heavily influenced how everything would turn out. One was the low pressure system itself, and the other was the approaching arctic cold front. To put it as simply as possible, the front was the driving force in pushing the system farther east and quickly out to sea.
Forecast Options: This scenario presented forecasters with a variety of possible outcomes. For example, if the system moved faster and the front moved slower than computer models were predicting, the system would track farther to the west, and bring us more snow. This is because the front wouldn't have advanced as far eastward by the time the snow arrived here, so it wouldn't be pushing the system as far to the east. However, if the system moved slower and the front moved faster than models were showing, the front would push it much farther to the east, and we wouldn't have even been close to getting anything from it.
Decision Time: In the days leading up to the event, the models were very inconsistent. In fact, one particular model run dumped 15 to 20 inches of snow right on top of us. I'm glad I decided to ignore that run! In general, though, models were going more with the latter option above, which pushed the system a little too far east to give us anything. However, experience has shown me that models often have a certain bias in those situations. It usually seems like the system moves a little quicker and the front arrives a little later than models predict. So, I worked that idea into my forecast as well. Feeling the system would shift a little farther west, I felt like we could get at least an inch or two of snow.
The Outcome: Fortunately, my thought process turned out to be right. The front slowed down and the system sped up, so it tracked farther west than the computer models had predicted. Unfortunately, our air became very dry, and it just didn't quite shift far enough west to give us anything more than a little bit of light snow. So, in theory, my forecast was pretty good, but with the dry air in place, I was a little too ambitious with my accumulation forecast of 1 or 2 inches.
Conclusion: Hopefully you now have a little better understanding of why such a forecast is so difficult. Very minor shifts either way in the speed of the system or the speed of the approaching cold front could mean a significant difference in whether or not we get anything in this type of scenario, and it's nearly impossible to predict with a high level of confidence.