Brief Mix Monday Night, Snow Possible Thursday

I want to first talk about Monday night. A small but potent storm system will race past the area and bring us rain generally from 7 PM Monday until 7 AM Tuesday. As colder air wraps into the backside of the storm, we could see a very brief mix of wet snow. As you can see from the maps below, temperatures will stay well above freezing, so all flakes (if any) will quickly melt on impact.





Now to the more complicated part of the forecast. Yesterday I talked about how the computer forecasts were in fairly good agreement on the track and timing of Thursday's storm system. The only wild card was the strength of the system. Well, it is looking like the computers are slowly trending to a solution: a weak storm. I've posted below snow outlooks from three different computer forecasts. None of them have a significant snowfall in our area.




We still have to watch this carefully. That patch of dark blue in North Carolina and southern Virginia represents about 1 to 3" of snow. If this storm shifts a little north, then we could have some light accumulations in central Virginia. This could cause problems for the morning commute on Friday. I encourage you to keep a close eye to the forecast through the week for the very latest information.

Now the discussion for all the weather geeks...

So you are probably asking yourself: why are storms falling apart in recent weeks? I think two factors are in play: La Nina and NAO. La Nina years are typically dry and mild. This wasn't the case earlier this winter because we had a persistent -NAO. NAO (North Atlantic Oscillation) is now positive, which I think is allowing La Nina to finally take over our weather pattern.

The map below is the overall upper-level weather pattern across the entire Northern Hemisphere (link: http://www.meteo.psu.edu/~gadomski/HEMI500/5dayloop.html). Notice the blue blob over Greenland and the Hudson Bay. This is an upper-level trough, or cold anomaly. In a -NAO pattern, it would be the opposite, a powerful ridge or blocking pattern. This allows storm systems to track up the East Coast, like what we saw earlier in the winter. We are not in this pattern any more.

Now, can we see snow in a +NAO, La Nina pattern? Yes, it's happened before. However, unfortunately for all you snow lovers out there, the odds are stacked up against you.

Update On Thursday's Snow Potential

As always, I want to start this discussion with a disclaimer. This is just a preview of the upcoming storm and not an official forecast. Things will change from now until Thursday.

The computer forecasts have been surprisingly consistent with the timing of this upcoming storm. In fact, they are now fairly consistent with the track. However, there are still some differences in the intensity. This will have a major impact on our forecast! Check out the maps below from two computer forecasts (ECMWF, GFS)



I will say this - that the second computer (GFS), has been very unreliable this winter. At this point, I leaning towards the first computer because it has been very consistent with this storm. I'm a little skeptical about its forecast accumulations, but I think our chances for snow continues to increase each and every day. For this reason, I've increased our snow chances to 60% on Thursday. Obviously it's too early to start forecasting snow amounts. We will continue to track this storm very carefully and bring you frequent updates in the coming days!

I've posted a couple maps below for the weather geeks like me. These are the 1000-500 mb thickness and mean sea level pressure for 1 PM Thursday. You can see how much more powerful the ECMWF is compared to the GFS (indicated by the tightly packed isobars).

Freezing Rain Tonight For Western Virginia

A batch of light rain and sleet (ice pellets) is currently moving across the area. Temperatures are in the mid and upper 30s, so all sleet is quickly melting on impact. As warmer air continues to move into the mid-levels of the atmosphere, we will see this mix change to all rain for Central Virginia this evening and tonight.

Although this a good news for us, it is bad news for areas farther west into the Blue Ridge, where surface temps will hover near or below 32 degrees. A Freezing Rain Advisory has been issued until 6 AM Saturday morning for Charlottesville, Lynchburg and areas to the west. Use extra caution if you plan on traveling westbound this evening and tonight because there could be some icy spots. Temperatures should rise into the mid 30s by late Saturday morning, and the threat for ice will be gone.