A recap of our second storm in a month

It is not often that we get two major, disruptive winter storms in the span of a couple of weeks, but here we are. Now that the snow and ice are all but gone, it is time to review some of the key elements of our forecast and compare them to how things played out.

We have always believed you deserve an honest, transparent assessment of the forecasts you depend on every day, and that is what we hope to provide. Evaluating our forecasts for high-impact events like this is key to ensuring we continually improve them over time.

Like the previous storm, this storm was not a surprise. We were mentioning the possibility as early as Friday of the week before, and our confidence in a forecast for wintry weather was high by Sunday evening:

During that evening’s newscasts and the video chat, Greg Fishel described his reaction to the outcome as “tickled pink.” There were some higher totals than we forecast for areas between the WRAL viewing area and the coast, including along U.S. Highway 70; however, within our area, the snow fell almost exactly as forecast.

We also took to Twitter and Facebook to alert you that this would be a big deal:

We always expected the storm to spread from south to north across the area, beginning Wednesday morning, and bringing precipitation to all of central North Carolina by the afternoon, if not before. Elizabeth Gardner was talking about this on TV and Facebook as early as Monday morning:

We continued to refine the timing as new model data came in:

While our FutureCast model suggested a slower timing, we were clear to frame that within the context that there was uncertainty about the exact timing, and that uncertainty should be factored in when making decisions:

If there was a shortcoming in our presentation of the forecast, it might have been that we were not more aggressive and consistent in emphasizing the potential for the precipitation to begin even sooner than noon, which was within the realm of possibilities. This might have prompted more folks to opt to stay home for the day or plan to leave work sooner.

That said, on Tuesday evening’s 11 p.m. newscast, Greg Fishel quite clearly showed that the precipitation would arrive in the Triangle around mid-day. Moreover – and more importantly – he emphasized that, unlike other snow events that start with flurries and gradually ramp up, the snow would come down steadily and heavily from the beginning. During our morning news on Wednesday, Elizabeth Gardner reiterated that point – and backed it up showing the snow on our Fayetteville Skycam. However, even knowing that the snow would come down quickly from the start, Greg said he was surprised at how quickly it began to stick to the roads.

As expected, the precipitation began as snow but changed over into a wintry mix during the afternoon and evening on Wednesday. We transitioned from our noon newscast into continuing coverage on the air, online and via social media to track the changeover. We also used our live cameras, Drive5, the DUALDoppler5000 and related technology to show you exactly where the changeover was happening and where it would move next.

The combination of the isothermal structure of the atmosphere, the track of the low and the system’s overall strength gave us more snow and less ice across the board than forecast, and the band of highest ice totals set up about a county farther inland as well.

The pattern general location of heaver vs. lighter snow in our forecast was good, but the amounts at any one location were generally underdone by 1-2 inches, or about 0.1-0.2 inches of liquid water in any one spot. For example, we forecast totals in Wake County to range from 1 inch in the east to perhaps 4 inches in the far northwest; the county averaged 4-5 inches with a few pockets of 6 inches. Near Fayetteville, this under-forecast was more significant: We expected the snow to remain only briefly before changing over to ice. The snow lingered and added up to 4-5 inches.

The flip side, of course, is that more snow resulted in less ice. Again, the pattern and orientation of highest totals was good, but location was off a bit, and amounts were overdone. This was providential in the end because trees and power lines tend to do better with snow than the higher totals of ice that would have happened.

With the caveat about onset and road conditions noted above, our overarching message was that travel conditions would deteriorate rapidly, from south to north, during the day on Wednesday and that travel would remain dangerous, if possible at all, through Friday morning. This was spot on, and while, in retrospect, we could have been more emphatic about these details, the message was clear: Stay home Wednesday, if you can, and focus any necessary activities as early in the day as you could.

Regarding power outages, we expected that areas mainly south of the Triangle would experience “scattered” to “widespread” outages, and that farther north, outages would be more isolated. For the storm, there were on the order of 100,000 customers in North Carolina without power at some point (and each “customer” means a business or home, most of which have more than one person). Most of those power outages lasted 12 hours or less, as conditions were still such that crews could get out in the weather and address them. Because the area has a couple million people, I would consider what we saw to be on low end of “scattered.” The lower number of outages was a result of there being more snow and less ice overall.

Fortunately, the final act for this storm – some wraparound snow during the day on Thursday – was underwhelming. We expected this to be a late-morning to mid-afternoon shot of mostly snow, affecting northern areas more than southern areas. The timing was again spot on; however, the amounts we forecast were overdone. This kind of precipitation generally sets up north and west of the track of the upper-level low, and because the upper-level low tracked farther west of here than we expected, so too did the highest totals.

It is rare for our part of North Carolina to be struck with two significant winter storms in the span of less than three weeks. Fortunately, both storms – and more importantly, their impacts on our day-to-day lives – were well forecast. Greg and I discussed last week’s storm and felt we deserved an A- or B+ for the week, with the highest grade coming Tuesday, Thursday’s underperforming snow weighing down the class average, and Wednesday’s forecast in the middle. We have already noted a couple of things we will work on for the next winter storm, whether it is next week or next year. Your suggestions are welcome, too!

Let’s talk about computer models for a moment.

Model guidance is an important tool for meteorologists, however, it is only one tool of many! To make a forecast, meteorologists use a combination of weather observations, forecasting techniques, knowledge of the atmosphere, awareness of the limitations of the computer models, forecaster experience, and, yes, computer model guidance. Likewise, your doctor will also conduct a physical exam; take a medical history; evaluate results from various tests and other scans; confer with other specialists; and refer to their own medical knowledge, experience, and past cases before making a diagnosis and recommending treatment.

Much like you wouldn’t want your doctor to diagnose you with a serious condition on the basis of a single tool – and if they did, you would demand a second opinion – you don’t want your meteorologist to make a forecast based on a single model map.

As a general rule, we do show model graphics on TV, online and via social media from time to time, but only when they help us explain a forecast (or some aspect or sources of uncertainty you need to be aware of). Even when we do not show those model maps, rest assured we see all the same data that are being posted everywhere. We incorporate ALL of this information into the forecasts we share with you on WRAL and elsewhere.

As always, we will focus our energy and time on taking all of the tools and information at our disposal and producing the most accurate forecast we can, day in and day out.