Winter Starting Early This Year
After a mild start to our week with temperatures reaching the 60s Monday, we're now starting the downward slide to what appears to be an early start to Winter weather. A cold front brought us some needed rain yesterday and while we've dried out this Tuesday morning...it's feeling quite a bit chillier as temperatures have dropped near and below freezing. We'll recover to the 40s this afternoon with brisk winds and some sun. However, another cold front will arrive tonight and yet another into Friday, making even 40 degrees a difficult number to reach in the afternoons as we reach the end of the week and weekend.
These changes center around a huge low pressure system in the Eastern Pacific. While this one will eventually weaken, otherwise will move in and take it's place, resulting in persistent abnormally low pressure in the waters southwest of Alaska. This in turn has buckled the jetstream, sending it well north into western Canada and forming a huge ridge in the Western U.S. This pattern change is partially responsible for the devastating wildfires that have developed in Southern California in recent days. In response to the jetstream moving well north in the West, it's taking a dip well to the south in the East in the coming days, forming what we call a large trough. When the jetstream has extreme northern and southern ends like this we call it an "amplified" flow or pattern.
This persistent trough will allow cold Canadian air to penetrate well south into the Eastern U.S. Each cold shot will be heralded by what we call an Alberta Clipper...a fast moving low pressure system that generally tracks from Western Canada down into the Great Lakes and Ohio Valley. The first of those will reach us late Saturday and it will likely result in our first widespread snowflakes of the season. The South Charleston parade may remain dry and chilly but by the time the Nitro, Hurricane and Huntington Parades are underway we may have some flakes falling from the clouds. As the atmosphere moistens expect more widespread snow showers by Saturday night areawide. The air will be dry and temperatures will initially be above freezing...plus the ground is warm so expect some melting in the lowlands. Nonetheless, the potential is there for the first coating of snow for many locations Saturday night with some roads perhaps getting a bit icy. In the mountains a couple of inches of snow appears likely, although the very highest spots have already seen some of the white stuff this season.
Behind that clipper temperatures will struggle to crack the freezing mark Sunday. A brief warmup to 50 Monday will be followed by another clipper on Tuesday with another round of snow showers likely. This pattern may last until to Christmas so the possibility of a White Christmas appears better than it has for years. Incidentally, the last widespread White Christmas in our area was 2010 when snow fell on the day itself. What's interesting is that we were in a similar pattern that December...what is called a "weak La Nina" where East-Pacific Ocean waters are unusually cool (the opposite of El Nino where the waters are abnormally warm). Looking at similar years about a month ago and comparing them with the setup we are currently in...I noticed the Winter of 2010-2011 bore similarities. That December was unusually cold and snowy and snow fell Christmas Eve and Christmas Day (I worked that Saturday morning and it was beautiful...especially with no traffic on the roads). The month ended as the 4th coldest December on record in Charleston. The severe chill relaxed a bit in January although it was still colder than average...then the pattern trended warmer and wetter in February and March. Overall snowfall ended up being close to average, with most of that coming early in the season. It will be interesting to see if the Winter of 2017-18 follows suit but one thing you can be sure of...Winter will be starting much earlier this year than last!