Alright folks, who hasn’t heard of the “big storm” coming this weekend? If you haven’t, you’re about to hear wayyy too much.
First off, simmer. The images you’ve seen of 12-18″ of snow for the Carolinas are coming out WAY too soon. It’s almost degrading to see mets (meteorologists or social “media”ologists) post about a storm of that magnitude so far out with such little confidence. If you follow any of those peeps, why don’t you go back after the event and see what they forecast last weekend compared to what actually happens. 🙂
So what is happening? Well, we have a classic southern tracker storm rolling in. Can you guess where it’s coming from? The Pacific! Take a look:
So what’s in question? Haha what isn’t in question is more like it. Snow, ice, sleet, freezing rain, regular rain – it’s all possible somewhere in the Carolinas. What makes forecasting in the Carolinas so hard is that we are pretty far south and during this time of the year there typically has to bea perfectly timed cold front approaching and precipitation match up. That doesn’t usually happen the way we want it (to get all snow at least).
Let’s dive into some specifics and also unknowns.
Something fun (meteorologically) will happen this weekend. A CAD (cold air damming) event is likely. What’s that you ask? Take a look:
This mess of an image is a Skew-T that I tried to label as neatly as possible. When the NWS (National Weather Service) launches a weather balloon, it has instruments that measure multiple parameters of different levels of the atmosphere (i.e. temp, dewpoint, wind direction, wind speed, etc.). This is the image it produces. It’s actually kind of easy to read. Where we stand on earth is the bottom of the picture – the atmosphere as we know above us – it the remainder of the image.
So look at the SFC (surface). Mind you this is for Charlotte in the middle of the storm. At the SFC, temperatures are below freezing but as you go up, lets say, 2500-3000 feet in elevation, temperatures rise above freezing! Say what?! Isn’t is supposed to get colder as you go higher up in elevation? Ladies and gentleman, welcome to the struggles of forecasting. That “warm” layer where temperatures are above freezing is about 4-6K feet deep. That’s big. Plenty of time for any frozen precipitation that falls through it to melt.
Another struggle….I’m showing you still images but the atmosphere is fluid as hell. So although the skew-t image above is for Sunday morning…by Sunday afternoon it could be completely different. Again, welcome to the struggles of forecasting winter weather in the southeast.
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Now it’s time for the unknowns.
1) TEMPS TEMPS TEMPS. We don’t know how much cold air will be in place. If this storm system is stronger, with stronger winds, we could assume that there would be more cold air getting infiltrated – we could also assume that there would be more moisture with is. And where is the moisture coming from? The Atlantic and the Gulf of Mexico. Very warms bodies of water. I sense another forecasting headache.
2) Timing. This storm is supposed to last from essentially Saturday night to Tuesday morning which means plenty of diurnal and nocturnal temp cycles to go through. Why is that important? Easy. Temperatures are usually warmer during the day and colder at night. Cloud cover limits day time highs and usually keeps overnight lows warmer. Ugh, another temperature issue.
Right now, we’re all (all of us meteorologists) using global models because those are the only ones that go that far out in time. Once we get a little closer, we can start using mesoscale models which have better solutions to issues like this…sometimes.
Wanna see some accumulation maps? I know I do!
Here’s the GFS and it’s thinkg (right now – as of Tuesday afternoon) of what to expect total for this event.
THE TAKE AWAY. We know something is going to happen. Models know that too. It’s really going to come down to temps right before and during the event to see what happens.
We also know that the Carolinas won’t be the only ones impacted by this storm. Remember it’s traversing across the country?
|RAIN likely to exceed 2-4″ in areas circled in red.|
|NATIONAL view of snow to come by next Tuesday. One model run – not a forecast!|
~Rain or Shine
I’m Andy Stein