Unsettled Weather Ahead
April 11, 2012 7:20 PM
We have had a nice run over the last few weeks; tons of sunshine, temperatures astonishingly warm, and very few things to complain about when it comes to mother nature. But it looks like the fun in the sun will be ending for at least a few days. A new very large trough will be diving into the western half of the country as we work toward the weekend, leaving much of the Midwest with plenty of cloud cover and areas of rain. However, it doesn’t look like it will be an all day gloom for days on end, but it is really tough to tell exactly where and when the rain will fall and just how much cloud cover we will have because of the massive nature of this particular system. Let me show you.
As you may know, troughs and ridges are commonplace in the weather world. Troughs typically mean cooler and wetter weather and ridges usually lead to warmer and dryer weather. Well, just like with everything else, you can have different sizes of troughs and ridges. This particular trough appears to be one of the largest we have seen in a while. Not to mention its going to be taking its sweet old time moving past us so things will probably stay unsettled for a while. But here comes the tricky part… when you have a larger trough, there are usually little storms that roll through the bigger overall picture. So as this huge system or trough is moving through, there will be smaller systems or troughs that move through with it, spinning about and creating their own thunderstorms. I realize this is a tough concept, but take a carousel for example. The whole carousel is spinning, but you have horses and elephants and donkeys that are inside of this carousel. The only difference is that these horses and elephants and donkeys will be spinning even faster then the overall carousel, kind of like the left lane of a freeway often moving faster then all of the other lanes. Below are a couple of images on vorticity, known as the spin in the atmosphere. This is most prominent in the mid levels and shows us where each little animal is inside of this big trough. The large trough is circled in white while the small troughs (animals) are circled in red.
Now with these little waves that move through the overall big trough, that’s usually where the showers and storms develop. Because of this, it’s becoming clearer that there could be 2 or 3 distinct periods where rain will be falling in our area. The first one will likely be sometime on Thursday as you can see in the image below.
The second and possibly third waves of rain will be Saturday into Sunday and then possibly Sunday night into Monday depending on the speed of this giant trough… the slower it is, the longer the precipitation sticks around. These second waves could be quite a bit stronger then the first. Check out a couple different models from the same time period. The first shows accumulated precipitation over a 6-hour period and the second over a 12-hour period.
Now even though the second model has quite a bit more rainfall, it is over a longer period of time. However, this would still give the area a solid 1 to 2 inches of rain, with locally as much as 3 by the time this whole trough has gone by. So there is the possibility of getting some really good rainfall over the weekend and early next week.
Here is the official rainfall forecast from the Hydrological Prediction Center spanning a 5-day period from 6pm Wednesday to 6pm Monday.
Now this shows that the southeast could get more then an inch of rain, but I would say this is a conservative estimate because a couple of the forecasting models that I have shown you show much of our area receiving as much as 3 inches of rain. So get ready farmers because the much needed rainfall that you have been asking for looks like is on its way. For the rest of us, an umbrella would be a good thing to keep close. Stay dry!