Friday, February 7, 8AM
During the cold stretch in January, the jet stream looked like a roller coaster with a big northern arc (ridge) over the western US, and a big dip (trough) across the eastern US. This is important because the jet stream acts as a boundary between warm air and cold air. An oversimplified explanation is that if the jet stream is to your north, it’s generally warm, and if it’s positioned to your south, it’s cold. Since we were in a trough through most of January, and the jet stream was south of us, arctic air was plentiful. Since that pattern broke a couple of weeks ago, the jet stream has stretched out and is now more zonal (west to east) without a big ridge or trough. The chatter among weather enthusiasts was that this period would probably be a break from winter until around mid month when the pattern looks to change again with a more “buckled” jet stream (and the pattern does look really good for the second half of the month). What no one really expected was that this period of zonal flow would give us multiple waves of winter weather, but that’s exactly what is happening. Waves of low pressure are sliding along the boundary, and depending on what side of the boundary we are on for any specific wave, we could have rain, snow, or a mix. This looks to continue for the next week or so with precipitation possible every two or three days.
First up is the system for tomorrow. Like yesterday’s event, this will also be slopfest. Some form of precip develops across the area around 1 – 2PM and continues into the overnight hours. Temperatures look to be a little bit colder for most areas, so tomorrow afternoon could be sketchy if you’re planning to be out. The one thing going for us is that it will be during day light so that should mitigate a lot of icing on roads, but know that by about 5PM, if temperatures are still below freezing, things could deteriorate very quickly with the setting sun. Tomorrow is a good day to find something to do at home.
After tomorrow comes the system on Tuesday/Wednesday that already has everyone talking. Right now it looks like we will be on the cold side of the boundary, and cold enough for accumulating snow. Models are about the same with timing which is Tuesday afternoon into early Wednesday morning, but are not in agreement on the exact placement of the boundary or the amount of precipitation. For now, just know that winter weather is likely beginning after noon on Tuesday, and it could be in the form of moderate snow. Any accumulation numbers you’re reading or hearing now are just a guess, and I’d certainly be skeptical of the big numbers that the GFS is tossing out. Some GFS runs have produced pretty snow maps that are a lot of fun to look at, but it has not been consistent from run to run so don’t believe them. The Euro has been more consistent with a moderate event that frankly looks more convincing. I’ll update periodically over the weekend.
The Weather Mill 