“The radar shows snow, why isn’t it raining at my house? The radar shows rain, and the thermometer says 4 degrees, why are we getting freezing rain?” The radar gives us an idea of what kind of precipitation is falling, but it doesn’t indicate what type of precipitation is actually hitting the ground. Right now, according to the radar, we should have had nice, light snow falling for quite a while. I believe by later today, we will have nice light snow falling, perhaps enough to lay down a fresh inch or two of snow. However, currently, the precipitation is doing battle with dry air. The precipitation is falling in the form of virga. The AMS glossary defines virga as, “Wisps or streaks of water or ice particles falling out of a cloud but evaporating before reaching the earth’s surface as precipitation.” You will often see these storms in the summer where it looks like the cloud is almost stretching to the ground. Some radars do a better job than others at omitting virga from the radar. the NWS radar. for example, does a fairly good job at eliminating virga from its display.
If you remember the December ice storm in Pittsburgh, the radar was green, indicating rain, not ice and the thermometer was above freezing. How did we end up with ice? If you remember that time period, we were leaving a significant cold period and had a nice layer of snow on the ground at the time. These two factors kept the surface temperature cold. So, when the warmer rain connected with the colder surface, we had freezing rain. Most of your point and click or media provided forecasts will likely show temperatures higher than mine and show less of a chance of snow. This is because the weather models both in the U.S. and Europe seem to be demonstrating a warm bias. And in case you were wondering, this is likely connected to the case for global warming that some politicians have been making. Although, if you noticed, people laughed when President Obama started talking about global warming during the State of the Union address, but I digress. Below is a 96 hour look from the European model, which seems to be handling mid-range forecasts the best right now, although none of the models have been great. You will notice a low over Ohio with blocking in Canada. I also expect a Bermuda high to be moving into place. These two factors should help make sure that in the northern Mid-Atlantic and Northeast get our share of precipitation.
OK, enough of the weather trivia, on to the forecast. Our next chances of snow fall between Tuesday and Wednesday and then again next weekend. It really has been the winter of weekend storms!
Sat: Cloudy possible snow showers later, 1-2″ possible
Sun: Partly cloudy, chance of sun in the afternoon, high around 26, low in the evening around 20
Mon: Cloudy with an outside chance of lake effect snow, high near 30, low 20
Tue: High in the upper 20′s and lows in the upper teens
