Usually about a week or so ahead of a potential storm, you might see a snowflake on your phone or someone might post a model on Facebook, prompting a lot of chatter on social media.
By then we get a lot of questions regarding specific amounts but we hold off. Some may think this is building hype or withholding information. However, there's a scientific reason why we wait until two days before a winter storm to forecast specific snow amounts.
When it comes to forecasting snowfall more than a week away, we can think of it like Pachinko board game.
In this game, you can control where you put the ball. With models, they know where the ball is placed by knowing the current conditions. Once you release that ball there can be a wide range of different outcomes. So that's why you can put too much stock in snow forecasts more the 5-7 days away from the event.
Now if you put that ball farther down on the board you lower the amount of potential outcomes. Similarly, when you forecast snowfall amounts when you get closer you lower that range of potential amounts. That's why we usually release our snowfall thinking about 48 hours away from the event.
A reminder about the reality of long range forecasts (thanks to @NWSKansasCity), why detailed forecasts are not reliable long ranges in advance. It is best to focus on the POTENTIAL for a winter storm later this weekend, but not get too focused on specific amounts just yet. pic.twitter.com/kyVRc2yANp— NWS Wakefield (@NWSWakefieldVA) December 4, 2018
So this a breakdown of the steps we take to make a winter weather forecast.
About 6-8 days out we recognize an overall pattern and see that snow is possible.
During the 4-5 day time frame once we start seeing more consistency in different models our confidence grows in whether or not we'll see winter weather.
Two to three days out we get more confidence in the timing allowing you to make plans.
Once we're two days out is when we show amounts and fine-tune the details giving you time to react.
So in the future, keep in mind if someone is telling you specific amounts more than two days out it's likely clickbait.
It's smart to stay keep our winter storm forecasting timeline in mind so you can properly plan with your family.