Weather! Still quiet, but I’m dreaming of a white…something?

I’ve got information about Christmas Day climatology from the National Weather Service, along with a quiet remainder of the workweek. As for this weekend…well, if this were Facebook, my status would be “it’s complicated.”

December 22, 2010; 9:26 AM • by Weather Dan

The National Weather Service office in Wakefield has released its annual review of Christmas Day climatology. Here are some of the highlights:

The average high and low for Richmond on Christmas Day are 48 and 29, respectively. The record high is 74, set in 1955, and the record low is 3, set in 1983. An actual “white Christmas,” with either measurable snowfall on Christmas Day, or at least 1” of snow on the ground at 7am that morning, is fairly rare for Richmond – each of the two criteria have about a 7% chance of being met. The daily snowfall record is 5.4”, which fell back in 1914. The record for greatest snow depth as measured at 7am on December 25 is 7” in 1908.

For more information, you can find the complete breakdown for both Richmond and Norfolk at the NWS Wakefield site (PDF).

Temperatures overnight stayed quite warm, only dipping into the mid 30s instead of the low 20s as forecast. Enjoy the mild (relatively speaking) as you go out to start your day today.

A weak area of low pressure is located over eastern North Carolina this morning, dropping some scattered rain and snow showers near the DC area. We won’t see much of it, and the system will move offshore later today. The low clouds that are draped across the city this morning will move out along with it, allowing skies to clear this afternoon and temperatures to climb. Highs for Wednesday will likely reach into the mid 40s. High pressure will move into the area overnight and into tomorrow; lows tonight will fall into the mid 20s.

We’ll see more of the same for Thursday, with high pressure keeping skies clear and allowing temperatures some room to fluctuate. Highs again will be in the mid 40s with lows in the upper 20s. Friday may see some increasing cloudiness, but should otherwise be similar, with highs in the mid 40s and lows in the mid 20s.

It’s after this point where things get quite hazy rather quickly. As I mentioned on Monday, the major models are in agreement that a coastal storm is likely to develop over Christmas Day and Christmas night. What they haven’t agreed on, however, is just about everything else. The model solutions diverge on everything from location, to to track, to duration. The worst-case scenario comes to us courtesy of the European model, which indicates that the snow – and it would be nearly entirely snow – would start in the afternoon hours Saturday, and continue through most of the day Sunday. Given the size and the intensity of the low being projected, it’s likely that significant snow would fall along most of the I-95 corridor from the VA/NC border north to New York City and beyond, one one of the busiest travel holidays of the year, and probably breaking some snowfall records in the process.

Ok, now, stop. Take a deep breath. Remember what I said? Worst-case scenario.

There are some strikes against this setup. From a model perspective, the Euro and UKMET (the model run by the UK’s Met Office) are the outliers. Historically, the Euro has been a strong performer with winter weather. This season, not so much – the Euro’s had a challenge with the systems we’ve seen so far this winter. From a meteorological perspective, the Euro setup requires several precise atmospheric factors coming together at once.

Am I confident that this is the solution we’re going to see? Absolutely not. However – if this does verify – this storm could potentially cause massive travel impacts along the Eastern Seaboard. If you’ve got any travel plans around Christmas, you need to keep an eye on this system and have a backup plan ready. Don’t make any changes just yet; as I mentioned before, there are still a lot of variables to this situation. A significant snowfall is far from guaranteed.

On the other end of the spectrum, the GFS, the main long-range American model, has essentially been “out to sea” with this system. While it still intensifies the low pressure off the coast, the track is more latitudinal than longitudinal, and heads out in the Atlantic, rather than moving up the East Coast. The chances of snow from this solution are practically zilch. In addition, the GFS is slower in the timing of the system; the low would pass east of Virginia 6 to 12 hours later than as predicted by the Euro.

We’re still 3-4 days out from the start of any potential snow at this point, and there’s still a lot that can change with this developing system. A shift in the track of the storm by 50 miles one way or the other would have a significant impact on how much or how little snow falls across eastern Virginia. This is a system that’s just beginning to develop and move across the United States from California, and a lot can happen in the time it takes for it to cross the continent. I’m having a lot of trouble divining exactly which way to go with this system, and while there are a lot of possibilities on the table, including the two extremes I’ve talked about and any number of possibilities in between the two, it’s hard to say for certain exactly what we’ll see when it finally arrives.

I’m pretty bullish on the chances of Richmond seeing some snowflakes; there’s going to be plenty of cold air in place when this system develops, so if we see moisture from the Gulf move in ahead of the low – a setup that’s called an overrunning event, because the moist air aloft overruns the cold air and precipitates out – we’ll see snow. That being said, I’m not prepared to make a call regarding when, where, or how much just yet.

I’m going to be traveling tomorrow and likely won’t be able to update anything here until Friday, but I will be paying attention and I’ll post an update then. If you’re traveling at all this holiday season, I hope you’re able to travel safely and celebrate your holiday of choice with those you love.

For the record, here’s my backup plan.

December 22, 2010 9:26 AM 1