What we did well

Identified the potential for a significant winter weather event five days in advance

On March 9, our article headline stated the forecast was “very difficult.” On March 10, we said “nailing down specifics … is simply not possible.” On March 11, we wrote “forecast confidence remains low at this time, and potential accumulations in the D.C. metro area range from just a little to a lot.” On March 12, we cautioned: “The snow amount forecast in Washington is still quite uncertain, as the region is predicted to lie on the edge of the storm’s sweet spot, and slight changes in how it develops and moves could be the difference between a bust and a blockbuster.” Communicated the uncertainty about the storm. We repeatedly stressed how hard the forecast was and how sensitive snow amounts would be to the exact storm track.

Nailed the short-range forecast for the immediate area. Our prediction of one to four inches of snow-sleet in the immediate metro area, made March 13 , was on the money. Not only that, we correctly captured the storm’s evolution including its start time, end time, when snow was most likely to transition to a wintry mix, and when conditions would be worst.

Forecast snow

Actual snow

Where we erred

Our first projection, released very early Sunday morning, called for two to six inches of snow south of downtown Washington and five to 10 inches to the north. Our second projection, released late Sunday evening, decreased the five-to-10-inch projection in our northern suburbs to four to eight inches and shifted the two-to-six-inch band a bit north. It took a third try, late Monday morning, to lower amounts to one to four inches in the immediate area and three to seven inches to the north and west, which were correct or close to correct. Our initial snow amounts projections were too high. While they were heavily qualified (we indicated low-medium confidence and high bust potential), they simply weren’t right.



Our final snowfall forecast over-predicted amounts in areas well north and west of Washington. Although northeast Maryland near the Pennsylvania border isn’t really our area of focus, our amounts were way off there, by a factor of two or even three.

We did not place enough emphasis on freezing rain and cold temperatures, especially south and east of the District. Temperatures fell more than we expected in this area, to near 30 degrees, and freezing rain lead to tree damage and power outages, which we did not predict or communicate.

Why we erred where we erred

Our initial snowfall forecasts for the metro region, which were too high on Sunday, were based a growing computer consensus that the storm would take a track ideal for snow in Washington. But by Sunday afternoon and night, the models began to shift — tracking the storm closer to the coast and bringing the rain-snow line into the metro region.

When we issue snowfall maps, we do so based on the best available information at the time. There was no effort to overhype the storm, but to simply communicate there was a legitimate possibility of significant snowfall. Yes, we know the models could shift and stated that. We indicated the predicted amounts were low-medium confidence.

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Then, as information changed, we adapted.

One could argue maybe we shouldn’t issue snowfall maps when confidence is low and they could be misleading. But, as the National Weather Service and some media organizations begin issuing snowfall maps up to 48 hours before a storm, we like to as well. If you think we should hold off and wait to issue a snowfall forecast until we are more confident, provide that input in the poll below.

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Our snowfall predictions in our northern and west areas resulted from the storm tracking even closer to the coast than we anticipated, even when adjusting for model shifts. The coast-hugging track pushed the mixed precipitation further inland, cutting back snow totals.

Finally, the surprisingly cold temperatures and disruptive freezing rain in our southern and eastern areas, which we did not account for, were due to a very strong area of high pressure to our north over central and eastern Canada (see above image). This high pressure wedged cold air east of the mountains and the intensity of the cold was poorly simulated by computer models. We leaned toward the colder models in our forecast for this event, but that wasn’t a big enough adjustment.

Summary

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This was a really complicated winter storm. Computer model forecasts of rain-snow line position and where the heaviest precipitation would fall were a constant moving target. Given the complexities involved, I think we did a reasonably good job with the forecast and communication of the storm, even if we made mistakes. No human being and no computer model got this storm exactly right.

If you compare our forecast for the immediate metro region compared to those from other forecast organizations made the day before this event, we did very well.

I’d grade our overall performance a B.

How about you?