December 16: Round 2

Round 1 was a decent snowfall for all of us in Central Ohio. I believe the only areas left disappointed would be north of a line from Marysville to Delaware, and even they got at least an inch of snow.

Moving on to Round 2, and we have a much more difficult forecast to try and nail. It's our typical mixed bag, splitting the area in half with snow north, rain south, and an icy mess in between. So who gets what? That's what I'll try and lay out for you.

The Setup
A second southern low in as many days will be racing in to the Ohio Valley.

This one has a lot more moisture, and more warm air to push up and over the cold air we have in place. For Southern Ohio, that means enough warm air reaches the surface to bring a cold rain all afternoon and night. But for Central Ohio, it's the split.

The Event
Between 3pm and 4pm this afternoon we'll see precipitation begin to overtake Central Ohio. Just about everyone should start as rain with our temperatures in the upper 30s, but as the sun sets, diurnal heating will leave us with tumbling temps.

What happens after sunset will be messy and hard to pin down for exact locations. So here's an idea of what we could see:

I don't think these regions I've drawn are set in stone, either. As with most of these scenarios, a small tug north or south could drastically change who sees what.

Frankly I don't think models have a good handle on this. Some want to give all rain to our area and others are much more aggressive with snow as far south as Circleville to Lancaster line. I want to stay somewhere in the middle, with the focus for transition right around I-71 (as usual).

I've also drawn the Rain/Sleet/Snow area much larger than what most local news outlets will because of that extreme uncertainty. We could see an interesting temperature profile on the 7pm sounding out of ILN with a big clash of cold and warm air aloft.

Prediction
This one is super hard to determine, but I've seen this type of storm a million times in Central Ohio, and nine times out of ten the warm air advances further north than anyone expects. Here's what I think snowfall looks like:

These totals could move north or south by as many as 50 miles depending on what the temperature profile looks like overnight. I'll be posting on Twitter as precip starts and give you updates on what changes we could expect to this forecast.

December 15: Round 1

Now that we're getting in to high resolution model range it's becoming clear that Round 1 of this storm may actually be a little more impactful that originally thought. In yesterday's post I suggested this would be a light coating of snow, and then we'd begin looking ahead to Round 2. Well now the latest model runs are suggesting a more robust system that could bring a couple inches to parts of Central Ohio.

The Setup
We're around 30° this morning for much of the area, and I don't think we'll see much movement in temps throughout the day. Clouds and a cold pool of air leftover after yesterday's system has us locked in just below freezing throughout.

This should do two things: allow us to at least start as all snow tonight, and bring road surface temperatures down to near freezing so snow can stick as well. That's not a great combination.

The System Moves In

Snow should start around 9pm for our southern counties and slowly fill the area. Where the question lies is how far north this warm air aloft travels. Right now I think areas north of I-70 stay all snow tonight, while areas south could see a changeover to sleet or freezing rain for a couple hours around 3am before it all moves off before sunrise.

This will mean a slick morning commute for most. A Winter Weather Advisory is in effect until 7am Monday for light accumulations and possible ice.

I don't have time to make a snow map for this system, but expect a widespread 1-2" around Central Ohio, with possibly as much as 3" in isolated spots south of I-70 if there isn't a changeover early tomorrow morning.

I'll be posting a lot more on Twitter as this storm approaches.

Forecasting the December 15-16 Storm

We're about 24 hours out from the start of what will be a long duration storm for us here in Central Ohio. There have been rumblings on the internet about this storm for the past 10 days, but I've purposely kept quiet on this until now because it was just too far out to speculate on until now.

This will be our first decent "southern low" of the year, even though it's originating in the southern Plains. The track will bring it up from Texas in to the Ohio Valley by Sunday evening:

But this isn't a quick hitter. After the storm moves through by Monday early morning, a secondary low, shown in New Mexico on the map above, will intensify and head up along the quasi stationary boundary by Monday afternoon, giving us our second shot of snow.

The details are still going to be tough to nail down, so here's what we know for sure:

Sunday Night
Tomorrow will be chilly, with temps in the low 30's and slowly falling as sunset occurs. With this, a light shield of precip will move in from the south. This should be all snow for most of the overnight hours.

It seems unlikely that we'll see any major accumulations out of round 1. Perhaps a nice dusting on the grass and a couple slick spots for the morning commute on Monday.

Monday during the Day
Temps will slowly rise to the upper 30s after sunrise Monday. Any light snow will switch over to rain before our second wave of precip moves in. This is the trickiest part of the forecast, because this will also bring a surge of warm air northward. There will be so many questions about how warm, how far and how long that surge sticks around.

Monday Evening
The system begins to pull away and we switch back over to snow. As of now I don't think this is a major snow maker Monday night, but the trends bear watching for sure. We could wake up with 1-2" in parts of Central Ohio Tuesday morning if conditions are right.

I plan on writing more tomorrow as the storm gets closer and we can get a better handle on precip types for our area. Stay tuned!