Midway through the month of December and we haven’t had much snow, temperatures are averaging out almost exactly normal, but it’s been a wet month. It’s not a surprise the cold air has taken a break. November was one the colder months the United States has seen in decades and ranked in the top 20 cold November on record. Often, but not always, after an extreme cold month, the atmosphere takes a break.
So what will the next two months feature in terms of cold and precipitation? Looking over the long range charts an active storm track along the southern tier of the United States is going to keep forecasters busy. These storms mean more rain for California, the Gulf Coast and the southeastern part of the country.
Our biggest snow storms generally happen when the southern branch of the jet stream and the northern branch join forces to merge cold, moisture and energy. We can get storms from either jet stream, but usually not as much snow.
If we get a storm from the northern jet stream it’s often starved for a lot of moisture and if we get a storm from the southern branch it often lacks the cold air, especially along the coastline to produce major snow.
It’s not quite as simple as a northern and southern branch. The polar and subtropical jets can become active over the Pacific Ocean and bring storms into the west coast which then moves across the country. You’ve likely seen the results of an active jet stream in California. The northern stream has brought copious moisture into the northern part of the state and there are signs the southern jet stream will bring more storms in the coming week.
The water vapor loop below gives you an idea how weather systems are crossing the Pacific, North American and then onto Europe.
There are 4 storms or weather systems which will impact the eastern half of the USA from now until the end of the year. I’m not going to attempt to nail down the timing of these because the final two are so far out. The first one is the remnants of the California storm from last week and will bring some light rain to the area Tuesday night. The second one will likely pass out to sea south of our area over the weekend, but will need to be watched. The final two will occur sometime from about Christmas Eve through the 29th.
The GFS loop of storms below takes us to Christmas Day. The purple areas represent rain or snow.
While I do expect some chilly air in the next two weeks, it’s not until later in the period that we may see some arctic air. There’s also a reasonable chance the arctic air holds off until the first week of January, leaving us without a significant arctic outbreak this month. For snow lovers, we need to have enough cold in place when a storm impacts the area or all that moisture is likely to go down the drain. I’ll be watching the long-range model trends the next two weeks to see which way things are leaning.
Most forecasters felt this was going to be a winter with normal or above normal snowfall. If the arctic air fails to materialize at the same time we are seeing moisture, it’s certainly plausible for a wet winter with below normal white along the coast, but lots of snow inland and in the mountains. I haven’t seen any refining of forecasts yet, but as we close out December in 2 weeks, we’ll have a better idea of January and beyond. We’ve got a long 12 weeks ahead.