Martinsville Weather - Winter Storm Forecast Review for Mon 12/5/05
Long Range Forecast: My long range forecast for this storm actually ended up being pretty good. I predicted rain 10 days in advance, and kept it in my forecast. I didn't add snow into the forecast until 3 days beforehand, but since we ended up not getting much snow anyway, my long range forecast really wasn't too bad.
Short Range Timing Forecast: This was a critical factor related to how little snow we ended up getting. Precipitation was supposed to begin around 4 AM Monday (as rain), then change over to snow by mid-morning, and end between 4 and 6 PM. However, the entire system was about 4 to 6 hours ahead of schedule, as the rain begin around or just before midnight Sunday night, and the precip ended around 1 or 2 PM Monday. Because the storm was several hours ahead of what was predicted, we got much less snow. The changeover to snow still occurred when it was supposed to, but by that time, most of the precip had already moved through the area.
Precipitation Type Forecast: In northwestern Henry County, this part of my forecast was fairly accurate. The precip changed from rain to a snow/sleet mix around 8 or 9 AM Monday. However, it never really changed over in southeastern Henry County. Some places in that end of the county saw a little snow, but almost all of the precip fell in the form of rain. The cold air just didn't have enough time to make it that far south before the precip came to an end (which was earlier than expected, as I discussed above).
Temperature Forecast: My temperature forecast was fairly accurate, but slightly low. However, that was also related to the system moving through several hours earlier than expected. When moderate to heavy snow starts falling, there is an effect called "dynamic cooling". Basically, the coldness of the snowflakes helps to cool the atmosphere, and temperatures will tend to drop a few degrees when it starts snowing. However, we never really got any moderate to heavy snow, at least at the airport, and the temperature only fell into the mid 30s by about 9 AM and held there for the rest of the day. Had we gotten some heavier snow, the temperature most likely would have dropped into the lower 30s.
Accumulation Forecast: Since most of the precip fell as rain instead of snow, my accumulation forecast was way off. My early guess of 1 to 4 inches actually ended up being the most accurate, even though it was still too high. But I upped my forecast to 3 to 6 inches in Saturday evening's update, which turned out to be the wrong decision. However, in my defense, one computer model was predicting upwards of 1.5 to 2 feet of snow at that point, so a forecast of 3 to 6 inches (at least at that time) was certainly reasonable. I should have lowered it to 2-4" or 1-3" Monday morning just because the models weren't predicting as much precip over this area anymore, but I still felt like most places would get at least 2 or 3 inches. As it turned out, I don't think any location got over an inch, and most places got a dusting or no accumulation at all.
Conclusion: I should have stuck with my forecast from 3 days earlier (the previous Friday), because I was predicting "rain, possibly mixing with snow late" for Monday and not much in the way of accumulation. Unfortunately I decided to change it, and my forecast got much worse. I give myself a grade of C- for this storm. Overall, I had the right general idea of how the storm would evolve. However, two main factors--the storm moving faster than expected and the cold air not reaching the southern end of the county--caused my forecast to end up being rather inaccurate.
Review my forecasts:
7 AM Monday 12/05
8 PM Sunday 12/04
8 AM Sunday 12/04
8 PM Saturday 12/03
8 AM Saturday 12/03
7 AM Friday 12/02
7 AM Thursday 12/01
7 AM Wednesday 11/30
7 AM Tuesday 11/29
7 AM Monday 11/28
8 AM Sunday 11/27
8 AM Saturday 11/26
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