Monday, February 13, 2006
Assessing the Past, Predicting the Future...
Jason Samenow @ 12:00 AM
After a snowy weekend, it's back to work and back to school (for some, not others). Be careful when you head out this morning, as icy spots are likely given low temperatures in the low 20s downtown and in the teens in the suburbs. We'll see a good deal of sunshine this afternoon with temperatures reaching the upper 30s. These conditions will allow for plenty of melting.
After every significant winter storm, CapitalWeather.com evaluates its performance. What follows is an objective as possible self-evaluation:
Were we succesful in identifying the storm threat well in advance? We first identified the potential for a coastal snowstorm last Sunday in our "Snow Lover's Crystal Ball". We mentioned it every day subsequently, initially (Mon-Wed) as a low probability event (20-25%), but by Thursday indicated it was a high probability event (66%). We might have trended up probabilities more gradually, but were successful in recognizing/communicating the potential for a storm almost a week ahead of time. Grade: A-
Were we consistent in our forecasts? Our forecast accumulation forecast of 4-7" was made Thursday night (or Friday morning) before any other media outlet. As guidance came in suggesting the storm would be more significant, we bumped up forecasted totals to 5-8" on Friday evening, and to 6-9" Saturday morning. While conditions warranted our gradual upward adjustments to the accumulation forecast ahead of the storm, unlike almost every other media outlet, we did not alter our forecast during the storm. In general, we told an internally consistent story and stuck with it. Grade: A-
How accurate was our forecast for the storm's evolution/impact? We correctly stated that most of the accumulating snow and the storm's greatest impact would occur overnight Saturday. However, we did not forecast the rain that fell Saturday morning into the mid afternoon hours instead forecasting light (non-accumulating) snow. In practice, there isn't much difference between light rain and light snow that doesn't stick, but we made a mistake by assuming surface temperatures would be cold enough to support snow during this phase of the storm (which resulted from the lack of a cold high to the north). Grade: B+
How accurate was our forecast for the storm's intensity/accumulation amounts? Our forecast of 6-9" in the metro area was a bit low, as totals ranged from 6-16". Our greatest underestimates occurred in the north and west suburbs. Nonetheless, we did indicate that we wouldn't be surprised if there were some double digit totals if convective snows developed (as they did) and correctly stated the heaviest totals would probably occur to the northeast of DC (Howard County received the heaviest snows). Grade: B+ (Related article: Some Get a Dusting, Others Still Digging Out)
Overall Grade: A-/B+
How did other media outlets do?
Given the length of this post, the week ahead preview this week will be abbreviated. We will experience a significant warming trend through midweek, with dry conditions and temperatures reaching the 40s Tuesday and 50s Wednesday and Thursday. A strong cold front will bring the threat of rain showers Friday, before much colder air (highs in the 30s) returns for the weekend. There are some early indications a storm with the potential to bring wintry precipitation to the area may develop late in the weekend or early next week. For more, keep reading....
Snow Lover's Crystal Ball 
Next Chance of Accumulating Snow: Sun-Mon, Feb. 19-20
Probability: 20%
Potential Impact:
Commentary: Another area of low pressure could develop in the deep south by the weekend. The questions are: Will it really develop? How strong will it be? And will a huge area of Canadian high pressure suppress it to the south and east or will it head toward us like the last storm? Only time will tell.
Snow Post Mortem: Grading Our Performance, Assessing Others'
After every significant winter storm, CapitalWeather.com evaluates its performance. What follows is an objective as possible self-evaluation:Were we succesful in identifying the storm threat well in advance? We first identified the potential for a coastal snowstorm last Sunday in our "Snow Lover's Crystal Ball". We mentioned it every day subsequently, initially (Mon-Wed) as a low probability event (20-25%), but by Thursday indicated it was a high probability event (66%). We might have trended up probabilities more gradually, but were successful in recognizing/communicating the potential for a storm almost a week ahead of time. Grade: A-
Were we consistent in our forecasts? Our forecast accumulation forecast of 4-7" was made Thursday night (or Friday morning) before any other media outlet. As guidance came in suggesting the storm would be more significant, we bumped up forecasted totals to 5-8" on Friday evening, and to 6-9" Saturday morning. While conditions warranted our gradual upward adjustments to the accumulation forecast ahead of the storm, unlike almost every other media outlet, we did not alter our forecast during the storm. In general, we told an internally consistent story and stuck with it. Grade: A-
How accurate was our forecast for the storm's evolution/impact? We correctly stated that most of the accumulating snow and the storm's greatest impact would occur overnight Saturday. However, we did not forecast the rain that fell Saturday morning into the mid afternoon hours instead forecasting light (non-accumulating) snow. In practice, there isn't much difference between light rain and light snow that doesn't stick, but we made a mistake by assuming surface temperatures would be cold enough to support snow during this phase of the storm (which resulted from the lack of a cold high to the north). Grade: B+
How accurate was our forecast for the storm's intensity/accumulation amounts? Our forecast of 6-9" in the metro area was a bit low, as totals ranged from 6-16". Our greatest underestimates occurred in the north and west suburbs. Nonetheless, we did indicate that we wouldn't be surprised if there were some double digit totals if convective snows developed (as they did) and correctly stated the heaviest totals would probably occur to the northeast of DC (Howard County received the heaviest snows). Grade: B+ (Related article: Some Get a Dusting, Others Still Digging Out)
Overall Grade: A-/B+
How did other media outlets do?
- Channel 9 led the way in consistency with forecasts all in the ballpark of 5-8". Grade: A-/B+
- Channel 7 was also pretty consistent with forecasts of 6-10" until they unfortunately decreased them to 4-8" Saturday night at 11pm. Grade: B+
- The National Weather Service had the best final call of 6-12", but wavered quite a bit with an initial forecast of 4-8" followed by a sharp increase to 8-14" before settling on 6-12". Grade B+
- Fox 5 was consistently too low -- with forecasts of 3-5" (Friday) and 4-6" (Saturday). I do give Sue Palka props for correctly and effectively communicating the fact the storm was just getting going at 10pm Saturday night. Grade: B
- The John Kerry award for flip flopping goes to Channel 4. Channel 4 first called for 5-9" (Friday and Saturday morning), then decreased totals substantially to 3-6" (Saturday at 6pm) before (prudently) upgrading them to 5-8" just hours later (Sunday at 12am). Grade: B-
- Related article: Fickle Storm a Test of TV Divination
Other Storm Notes
- Be sure to check out the map of snowfall totals across the area generated by reports from dozens of CapitalWeather.com visitors. Thanks to all of you who submitted totals. The map is cool!
- CapitalWeather.com photographer Kevin Ambrose has a nice gallery of storm photos.
- During the storm we received 1,166 comments from CapitalWeather.com visitors (this does not include the hundreds of comments received before and after the storm). The comments were interesting, insightful and polite (I did not have to edit or delete any), and we hope we were able to answer questions that came in. We were pleased to have several local TV meteorologists stop by and offer perspectives and answer questions. Thanks to all of you took part in the action.
- I'm sure everyone knows that this storm had a huge impact in the Northeast, with all-time record snowfall accumulations in Central Park, NY and Hartford, Connecticut. See this NY Times article: Wind and Snow Strike 14 States; Record Accumulation in N.Y.
The Week Ahead
Given the length of this post, the week ahead preview this week will be abbreviated. We will experience a significant warming trend through midweek, with dry conditions and temperatures reaching the 40s Tuesday and 50s Wednesday and Thursday. A strong cold front will bring the threat of rain showers Friday, before much colder air (highs in the 30s) returns for the weekend. There are some early indications a storm with the potential to bring wintry precipitation to the area may develop late in the weekend or early next week. For more, keep reading....
Next Chance of Accumulating Snow: Sun-Mon, Feb. 19-20
Probability: 20%
Potential Impact:
Commentary: Another area of low pressure could develop in the deep south by the weekend. The questions are: Will it really develop? How strong will it be? And will a huge area of Canadian high pressure suppress it to the south and east or will it head toward us like the last storm? Only time will tell.
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