Snow or No Snow This Weekend?

The model giveth and the model taketh away. Whether you want a big storm or 70-degrees and sunshine, when we're peering into the future more than a few days ahead, computer model data is all we have to go on. And while weather modeling has becoming increasingly accurate over the past few decades, we sometimes tend to forget that the solutions they give us aren't real. The pretty graphics they generate are based on many approximations, and regardless of how great a storm might look several days away, any one model is only as good as its initial conditions. If it fails to resolve a feature in the atmosphere when it initializes, it will give an incorrect solution for the future. That's why we often approach the extended forecasts with due caution, knowing good and well that things can and will change, even if every model out there shows the same thing. We've seen some pretty big changes in the model forecasts in the past 24 hours for the potential snow this Sunday, and it now looks less likely we'll see much of a storm. But before you write this one off completely, understand that we could just as easily see a move back in the other direction over the next day or two. The system is just now coming on shore near Seattle and Portland, and the models should have a better handle on what it will do in subsequent runs.

Here are a couple of things I like and don't like about the potential for snow this weekend: I like the fact that this is a pattern that has been depicted by the GFS model for over week now. It looked like something could happen around the 17th-19th of the month, and the system is due on the 20th. I also like that while the models are in agreement with a more southerly track that doesn't effect Virginia much, at least all of the models are showing a storm in the region. You can't have a storm shift it's course north if it's not there to begin with. I don't like that the main vort max becomes nearly cut off across the southwest U.S. on Friday. Cut off lows can be a nightmare for forecasting. I also don't like the lack of a Greenland block. Even the most aggressive model takes the storm on a SW to NE track, which has a much better chance of completely missing us to the south. If we had more of a blocking pattern (indicated by a negative phase of the North Atlantic Oscillation (NAO)), this would allow a more southern extent to the cold air, and would also cause the storm to track more S to N, or right along the coast. And the last red flag, and a very important one, was the lack of near-freezing surface air during the time of the event. Our in-house model generated a whopping 0.7" of snow yesterday when the Euro model looked its most impressive. Similar to what happened here on Saturday, it can pour snow, but if temps are in the mid to upper 30s, it won't amount to much. But again, it's a model, and it too will change.

So all this leads to me making no changes to my forecast for Sunday. I'm leaving us at 40% for snow, and won't move it until we get a little closer. As I type this, the midday GFS run has completed through the weekend, and is more favorable for snow. But I don't like the midday and overnight model runs. Confused yet? Be ready for snow on Sunday, and a plan for some decent weather as well. Mother Nature will take care of the details. -ZD

Weather Blog: Snowfall Forecast

I was sitting at the dinner table with my wife last night complaining about how this time of the year is the worst for a sports fan like myself. As passionate as I am about weather, my love of sports is not too far off. The NFL is over, as is college football, the NCAA tournament doesn't begin for another month, spring training for baseball hasn't started, the PGA tour schedule is pretty weak, and I've never been a big fan of the NBA or NHL which are in full swing. I'm certainly blessed with a great family and friends, and a few hobbies, but I still tend to get bored without a good lineup of sports on the weekend to either play or watch, or...some interesting weather to forecast. It's just a minor event, and the term itself might even be a stretch, but at least Mother Nature has thrown me a bone this weekend and given me and other snow lovers something to be excited about. The system arriving this weekend will come in two waves. We'll have a round of rain overnight tonight, with a round of light snow late Saturday night. The state of West Virginia and the mountains of west-central Virginia will see a decent snow, with Snowshoe Ski Resort likely enjoying around 10" of powder for the weekend skiers and riders. Amounts in central and eastern Virginia will be far less, ranging from and inch or two across northern and eastern VA, to a dusting to an inch across Richmond and vicinity. The snow will occur after dark in the metro, likely occurring between 9 PM and 2 AM, adding the perfect romantic touch to lovers out on a late night stroll enjoying an early Valentine evening together. Wow, did I really just type that? Anyway, whatever falls will be blowing around mightily on the backs of northwest winds of 15-25 mph. A little light snow collected next to the dog house or on a parked car could be all the evidence left of the system by Sunday morning. I'll have a fire going, the TV off, and a fiercely competitive game of scrabble going wife my wife Saturday evening as I wait for the first flakes to fall. The graphic above is my snowfall forecast through Sunday morning. I'll have updates on my facebook page, so drop by and send me a note and hit the "like" button while your there. Feel free to share this with others, and have a great weekend. -Zach

Weekend Weather Preview

A strong storm system will move through the Mid-Atlantic Saturday, and we'll start to see the signs of it today as cloud-cover increases over us from the west. Here's the early Friday morning infrared satellite picture of the U.S.:

I'll point out two features to you. The first of note is the cold front also associated with the clouds you see moving through the Upper Midwest. That front will move through Virginia Saturday. The second feature is the low pressure system tracking from Texas and pulling in moisture from the Gulf of Mexico into the Mississippi Valley region and the Southeast. As these two features converge in the Mid-Atlantic Saturday, we'll have rounds of cold rain in central Virginia, with snow in the mountains of western Virginia in the colder air. However, as that cold front sweeps through along with the digging upper trough (see the 500mb vorticity picture Saturday evening below) and brings in deeper, colder air, we'll have more snow mixing in with the rain Saturday afternoon and after dark.

It currently does not look like there will be any chance for an accumulating snow in the metro, as surface temps should remain well above freezing during the time of the precipitation (in the 40s). A winter weather advisory will likely be issued for areas to our northwest on Saturday (especially along I-81). After the surface cold front passes Saturday afternoon and evening, you can expect windy and much colder weather, with wind chills plummeting into the 20s and teens. If you have Saturday evening plans, be prepared for a blustery, cold night out! There may be a quick burst of snow in central Virginia on the back side of this storm system as that good upper-level energy passes overhead, including in the Richmond Metro, between 7 p.m. and 11 p.m. Saturday. This may lead to a dusting of snow on vehicles and roofs, but no significant accumulation is expected. Here's one forecast map (NAM) of snowfall potential from that final gasp of snow Saturday night:


Sunday will be mostly sunny, very cold with high temperatures struggling to get out of the upper 30s, and also a bit windy behind Saturday's system. The air mass will moderate some on Monday before the next storm system arrives Tuesday morning. The temperature profile for this second storm system will be similar to Saturday's, with the best chance of wintry weather lying just a little north of Richmond.

Stay with CBS 6, we'll keep you ahead of the storm.
--Meteorologist Carrie Rose
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