Predicting snow days by algorithm: How reliable is it?

The algorithm on, a free school-closings prediction service, predicts a possible but unlikely chance of closing or delay for the morning of Jan. 6. FCPS students must wait until then to see if the calculator is correct in its prediction.

Kate Deng and Anjali Khanna

Around this time last January, students of Fairfax County Public Schools (FCPS) had already experienced several severe-weather related closings. So many, in fact, that it seemed these students were checking Accuweather’s Snow Day Predictor on the daily.

Thanks to the FCPS School Board, with member Ryan McElveen reporting their every move on Twitter and Facebook to keep the county updated, FCPS received eight snow days last year, including St. Patrick’s Day, National Pancake Day, and Valentine’s Day.

However, just how reliable are algorithm-based snow day calculators like Accuweather and, which utilize information like area code, school type and leniency of school board members in granting snow days as factors for a forecast of upcoming closings?

“Although I do not rely on the predictions of snow day calculators alone, they serve as an informed second opinion regarding the matter at hand. However, precedent has demonstrated that they are, all in all, fairly accurate and reliable,” junior Fudong Fan said.

During the streak of snow in January of last year, most of the snow day calculators issued prediction values of 90 to 100 percent for the majority of the snowstorm days, meaning schools were “likely” to “highly likely” to experience closings or delays. This year, however, snow day calculators have not been put into as good of a use in FCPS, due to the lack of snowfall in this season’s forecasts. The only snowfall of the 2014-2015 school year so far occurred during Thanksgiving break, but most students did not feel the need to check the forecast for a day off that they were already receiving.

“I didn’t use any snow day calculators over break because there was no snow in the forecast and I didn’t feel the need to check if we were on break anyway,” freshman Jade Wang said.

With reported predictions of around one inch across Fairfax County in the forecast for the morning of Jan. 6, many Jefferson students are hopeful that the FCPS school board will be willing to close or delay schools.’s algorithm predicts a 40 percent chance of a closing or delay, which, according to the key provided on the site, suggests “little or no chance of anything, but possible.” Taking a slightly more optimistic tone, the Accuweather algorithm predicts a “four out of 10” chance for closings, meaning “possibly.” However, the latter algorithm does not take into account the number of snow days already spent nor type of school.

As a result, FCPS students can have no guarantee of school closures, and many will be waiting patiently for news come the morning of Jan. 6. However, the decision of the school board may prove to be a helpful indicator as to just how accurate snow day calculators are.

“I usually keep Accuweather page and snow day calculator open while I do my homework and check the FCPS website in the morning for updates, which is definitely what I will be doing first thing tomorrow morning,” sophomore Rehan Madhugiri said.