Let’s look first at why meteorologists are starting to crow about the pattern. When we compare the high-altitude weather pattern (at around 18,000 feet) centered on Jan. 11 (on the left below) with the pattern averaged over some of our snowiest winters (on the right) on record, we see a lot of similarities.
Note that both maps show a large area shaded in red across Greenland and Canada and a stretch of blue across our southern states extending out into the Atlantic. The red areas indicate high pressure to the north, which feeds in cold air. The blue shading across the south on both maps suggest zones of low pressure or storminess, which provide moisture.
The high-pressure zones of northern Canada and Greenland reflect the negative phase of the North Atlantic Oscillation, which can be quite favorable for snowstorms in the Mid-Atlantic.
But sometimes these zones of high pressure in the high latitudes push the storm track too far south of Washington. That’s what most of the models are forecasting for the storm slated for Friday and Saturday. While it could bring some snow to western North Carolina and perhaps southwest Virginia, our area will probably miss most of the precipitation unless the storm track shifts north.
The other factor working against snowfall is marginal temperatures. The air to our north is not very cold as most temperatures in Canada are well above normal. That air still could be cold enough to support wet snow with high pressure to the north feeding cold air south. However, unless precipitation falls heavily, temperatures may not fall enough for snow to accumulate, or cold rain might even fall.
If Friday’s storm misses, models are advertising the possibility of another storm coming up from the south next Monday. For this event, the predicted storm track may be far enough north for precipitation to reach the region, but the question will be whether enough cold air will feed into the region for accumulating snowfall.
Overall, the pattern is improving and we have a couple systems to monitor but it would be better for snow if the jet stream climbed farther north into Alaska so that it could take a deeper dive over eastern North America. This would draw true Arctic air southward. For now, snow prospects are trending upward but are far from perfect given the limited cold air supply.
Finally, it’s worth pointing out that models sometimes predict very favorable snowstorm patterns that don’t materialize. And very favorable snowstorm patterns don’t always produce big snowstorms. Lots of ingredients have to come together.