Here's why Maryland's snow forecasts doubled at the last minute over the weekend

On Friday, meteorologists were calling for a light snow and a few inches of accumulation in the Baltimore area over the weekend.

But by Saturday morning, it became clear a storm capable of dropping significantly more snow was materializing. The forecast jumped from about 2-4 inches to 4-8 inches, and the worst-case scenario rose from about 5 inches to 10 inches.

Across the region, snowfall ended up ranging from 5 inches to 10 inches.

Why the last-minute change in forecast?

» Weather models aren’t perfect. They always come with a margin of error, because different weather models sometimes come up with different guesses for total precipitation. They take current conditions into account and use them to project the future based on the past. Each model has different strengths and weaknesses, and as the snow closed in, forecasters began using short-term, high-resolution prediction models that showed…

» The snow ended up lasting significantly longer than earlier weather models had suggested. On Friday, meteorologists said it would start Saturday afternoon or evening and possibly taper off by 10 a.m. Sunday. Instead, it was mostly uninterrupted from Saturday night through Sunday night. That was because…

» The storm had more elements to it than meteorologists initially expected. It came from the Midwest, dropping snow from Kansas to Ohio and moving into the Mid-Atlantic. On Saturday, it began to transfer its energy to a low-pressure system off the coast of the Carolinas. And then Sunday, it was trailed by another low-pressure system higher up in the atmosphere. Meteorologists weren’t sure both of those elements would affect Maryland, but the second phase in particular produced more snow than meteorologists had predicted.

More: Weather-related closings and delays »

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