CWG Gets Credit For a Correct Forecast, But...
Weather Checker is an outsider's analysis of CWG's forecast accuracy. See previous Weather Checker posts.
By Jamie Yesnowitz
Well, Washington finally got a real winter storm, and in the end, CWG's Saturday prediction of several inches of snow across the area late Sunday through early Monday did verify. But the devil truly was in the details, particularly in the coverage several days out, and the late-breaking change in prediction on Sunday night.
Keep reading for the Weather Checker's full review...
Prior to the Storm
The long-range forecast starting about a week out was poor. CWG's Monday forecast (by Jason Samenow) did not hint at significant winter weather, predicting with medium confidence seasonably cool high pressure over the coming weekend, with highs in the 40s on Sunday. The Tuesday forecast (by Matt Rogers) did note the potential for a "wildcard" over the weekend, but in looking at the prevailing pattern of the winter, dismissed it as "a minor worry, and something just to monitor in the days ahead."
By midweek, CWG's Wednesday forecast (by Dan Stillman) predicted with low-medium confidence a wintry mix over the weekend, with temperatures that "may be warm enough to favor rain and limit the impact of any snow or sleet." If this prediction was solely related to the brief period of mixed precipitation that came through Saturday night, then it came true, but it was unclear whether the forecast specifically applied to Saturday night or the whole weekend. Then, the Thursday forecast (by Camden Walker) missed, expecting with low-medium confidence that any precipitation Saturday night and Sunday would wind down Sunday night with partial clearing, and with medium confidence that Monday would be mostly sunny. A similar forecast was issued by Ian Livingston that afternoon. The Wednesday and Thursday forecasts incorrectly viewed the Saturday night and Sunday night storms as one discrete event.
On Friday, the forecasts came into much better focus. The Friday morning forecast (by Josh Larson) was the first to directly address the two-storm potential, noting that while there was a chance for wintry weather on Sunday night and Monday, there was a decent chance of a miss to the south and east. A midday Snow Lover's Crystal Ball (by Dan Stillman; updated that evening), noted with low confidence a 50-50 chance of snow, and also mentioned the possibility of a miss to the south and east.
By late Saturday morning, it became apparent that a storm was likely to affect the Washington area. That day's Snow Lover's Crystal Ball and Saturday night update (both by Jason Samenow) were spot on with respect to expected accumulations, including the potential for bigger accumulations south and east of the city.
Timing as Storm Approached
CWG's Sunday morning Team Forecast timeline, which called for accumulation to start between 4 and 8 p.m., was accurate for areas several miles south and east of the city. But it was way off for D.C. and points north and west, where there was little or no accumulation until after midnight, thanks to light and spotty precipitation along with temperatures substantially higher than forecast.
This first part of the storm proved yet again that a 20-mile miss can make all the difference in the world. While one can hope that long-range forecasts (e.g., several days to a week out) can improve as models and meteorologists advance, I'm not sure that errors as small as 20 miles will ever go away.
The Sunday night backtrack in the forecast was a bigger mistake. I've never been a fan of nowcasting. And as the first half of the storm came and went with little fanfare and not much accumulation northwest of the city, the team changed its forecast, lowering snow amounts substantially for locations north and west of the Beltway.
One question from my end is whether, prior to the change in forecast, CWG considered that the energetic upper-level area of low pressure -- which overnight into Monday morning delivered the accumulations originally predicted -- could possibly draw energy out of the surface low pressure responsible for the first half of the storm.
Also, did the negative comments that streamed in when the first part of the storm fizzled in any way contribute to CWG's decision to change its forecast? I would hope not. In any event, the flaw in adjusting the forecast, in my view, was more egregious than the flaw in timing.
Ultimately, CWG was correct in its initial take of what proved to be an oddball storm, both in terms of its higher accumulations south and east of the city, and the fact that it occurred in early March. In high school math class, I got some credit for getting the answer right, but only got full credit if I could show the teacher how I got to the answer. Likewise, while CWG's initial forecast was correct, the way it verified was not ideal.
About the Weather Checker...
Jamie Yesnowitz has been interested in the weather since he rooted for school-closing snowstorms while growing up in Brooklyn and East Rockaway, N.Y. After graduating from Dartmouth College with a bachelor's degree in economics and government, his focus on the accuracy of weather predictions took hold when he moved to Coral Gables, Fla., to attend the University of Miami School of Law. Class was scheduled to begin on August 24, 1992. Hurricane Andrew had other ideas, however, shutting down the school for weeks. But what stuck in Jamie's mind was the final unpredicted swerve of the eye that saved those living in Miami and points north, and completely devastated areas about 20 miles south of Miami.
Undeterred by the hurricane, Jamie ultimately served as editor-in-chief of his law school newspaper, and earned both a juris doctorate and master's degree in taxation. Following law school, Jamie practiced corporate and securities law in New York before shifting to the state and local tax consulting world. Jamie moved from New York to the Washington area in 2003, and he is presently a state and local tax senior manager at a major accounting firm. Jamie lives in Potomac with his wife, Sandra, and their two daughters, Sarah and Carly.
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