MikJournal Monday 11/26/2018...Terminology Explained

Good morning to you. Waking up this morning to a blustery start as temperatures have crashed overnight. My temperature at midnight was 51 degrees thus my high temperature for this day. However, presently at 10:15 a.m., I have a reading of 36 degrees, up one degree over the past few hours, and even experienced a few light snow showers.

Let me update you on Lexington's annual precipitation total. As I write this, a total of 65.57" has been tallied so far this year. The all-time record is 66.35" set in 2011. Therefore, a difference of just 0.78" is all that separates Lexington's all-time wettest year, or at least a tie.

A blast of cold air will reside in our region for a few days this week. In an earlier post, I mentioned about the Arctic Oscillation and its effects on our weather. Forecasts for a V-shaped signal caught my attention. Typically, I have noticed after the AO has taken a dive into negative territory, then quickly bounces back, rising toward the neutral line, an influx of milder air or return flow begins moderating our temperatures a bit. Often this introduces moisture into our region. Along with cold air trying to get out of the way, at times, the moisture overwhelms the cold air and we end up with a winter storm scenario.

But, this is normally seen during the winter months, at least this feature of the teleconnections. Of course, the other teleconnections like the NAO, PNA, and even the EPO have to be aligned as well. Since November has been behaving much like December and January at times, it seemed that this V-shaped signal would correlate better. However, all weather forecasts now are pointing toward a milder week after this cold snap. Any precipitation chances appear when the milder air is already in place thus just plain rain for our region.

Nevertheless, keep an eye on this exciting feature during the winter months as this is generally a precursor for wintry weather somewhere in our region. But, you know how Kentucky is, the battle lines between varying conditions of precipitation are always a source of contention and frustration for snow lovers and experienced forecasters alike.

One more thing. This is more about terminology than anything else. When you hear a meteorologist explain that the "strong winds are a result of low pressure with tightly packed isobars, or areas of equal pressure", that doesn't really spell it out for us very well, does it? It doesn't mean anything to me.

What is really happening? At the core of the low pressure, you have the lowest pressure reading. Surrounding that, perhaps only a few miles away, a different pressure reading is taken and shared by other locations surrounding low pressure. A few more miles away is a different pressure reading again shared by other locations surrounding the "low". Those are your isobars or areas of equal pressure. Behind the actual "low" is rising pressure. Ahead of the low is "falling pressure".

What causes the wind gradient? Well, simple physics tells us that pressure flows from high to low. It is either a steep rise or steep drop in pressure over a relatively short distance that produces the wind. The greater the difference between high and low pressure over a relatively small distance, the greater the force needed to equalize the pressure disparity. Eventually, winds will subside, because high pressure (also known as subsidence) will create more calm conditions in time.

Have a good week everyone. The busy season is upon us.

MS