Fog Again and a Look Ahead

Here we go again.... more large expansive areas of fog. All of the recent snow melt has led to a lot of moisture being added to the lowest layers of the atmosphere. Well when that moisture gets trapped at the surface, you often get fog. Well visibilities are once again taking a beating tonight as many areas are below a mile and some cases, near zero. Here are the visibilities as of about 8:30pm this evening.Because of the large nature of the dense fog, dense fog advisories have been issued by the National Weather Service until 8:00am Friday. Here is where the current advisories are located.

I'm actually anticipating them (NWS) to expand their advisory area to include much of eastern South Dakota as the night wears on. If you are traveling sometime between now and Friday morning, use extreme caution because visibilities can drop very quickly especially in low lying areas.

We have seen a very calm few days across the Upper Midwest and I'm sure you are wondering why. The steering currents of the atmosphere called the jet streams are no where close to the Upper Midwest. Storm systems will ride along the jet stream like traffic on an interstate. But when there are no jet streams around for a storm to hitch a ride on, then there are typically no storms in that area. Its a tough concept to grasp but I will give you a visual. Look at the picture below.

This shows both jet streams that effect the U.S. The southern branch is called the sub tropical jet stream and the northern branch is called the polar jet stream. The current pattern we are in is called a split flow. This means that the sub tropical jet stream is to our (U.S.) south and the polar jet stream is to our north. With both jet streams hundreds of miles from South Dakota then there is very little likelihood that we will get a storm.

But for those of you who want more rain or snow I have some signs of hope. The longer ranged models are showing signs of a pattern shift as we go into next week. Both jet streams will likely be back over the U.S. which will cause an influx of storms. Here is what one of the models is showing for next weekend. Keep in mind that this picture represents liquid precipitation accumulation over a 12 hour period.

The next few days could be the calm before the storm so take advantage while you can.

~KDLT Meteorologist Cody Matz