Analysis of Forecaster Performance for Dec. 9 Storm

The final total for this weekend’s snowstorm was 10.5 at the official MSP airport recording station. The core metro area snowfall ranged from 9 to 14 inches with an even foot of snow a common observation, including here at TMF headquarters in St. Paul.

No forecaster anticipated the possibly of a truly major snowfall until late Saturday afternoon. Even then, most forecasts did not fully capture the extent of the burgeoning snowstorm. (Note, for weather geeks looking to get a meteorological explanation for the late-changing forecast, MPR provides a good analysis here.)

Rather than provide forecaster grades as we have in the past, we’ll focus on a few general observations. Given that we don’t capture forecast activity in a truly systematic, day-by-day manner, we feel that the assignment of grades suggests a level of authority and exactness we simply don’t have. Still, we believe we monitor the forecasts enough to offer reasonable opinions. As always, take them for what they’re worth. We invite readers to provide grades and thoughts in the comment section to this post.

Our observations:

The best performers for this storm were the National Weather Service (NWS) and Novak Weather. Most other forecast outlets did not distinguish themselves.

Virtually all forecasters eyed this storm for the better part of a week. However, several minimized the storm as recently as Thursday. On Thursday, KMSP tweeted, “Winter returns the next few days, flurries late Fri afternoon, flurries Sat and wicked cold by Mon.” On Thursday evening, the Star Tribune noted the possibility of 1-3 inches of “oatmeal-like slush,” jokingly suggesting it would be cause to contact MnDOT and the National Guard. Likewise, the Weather Channel noted the possibility of mere “snow showers” over the weekend. At the same time, however, other forecasters were not ready to conclude the storm would be a minimal, back-page item.

KMSP was Jekyll & Hyde on this one. After the overly minimizing tweet on Thursday, they had the best standing prediction on Friday night with a forecast of 6-8 inches. But by Saturday, they’d revised it downward to 4.1 inches (the “snow meter.”)

The NWS consistently predicted higher amounts than the majority of forecasters 36 hours prior to the storm’s arrival. Some readers/viewers may have wondered whether a winter storm warning for MSP would prove to be warranted; clearly, it was.

Novak Weather also lead the way on this forecast, staying the course of a forecast of 6+ inches for MSP from early on. On Saturday afternoon, Novak Weather was also the first to communicate the possibility that accumulations could “get out of hand quickly for MSP” on Sunday as they ultimately did.

The separation of men from boys on this forecast took place Saturday afternoon and evening. Some forecasters picked up on the late-developing possibility of a truly significant snowfall while others did not. As detailed in the previous post, forecasts by KSTP (Jonathan Yuhas) and KMSP (Steve Frazier) missed the boat in not noting the late change in the storm’s evolution (though it should be noted that other members of the KSTP forecasting team tweeted 5-8 inch forecasts at the same time Yuhas was on air forecasting 3-6 inches).