It's a great Tuesday bloggers!
Today, we will go over the set-up for Thursday's chance of thunderstorms and talk about summer "trying" to settle in during the next couple of weeks.
Let's start with this weeks developing weather pattern. Look below at the forecast map valid Thursday morning. This is the 500 mb map (around 18,000 feet up). This is really a great level of the atmosphere to look at the weather patterns as they flow across the northern hemisphere. The weight at the top of the atmosphere is 0 mb (no weight), and it is around 1,000 mb near the surface. So, 500 mb is about half way through the atmposhphere in weight and a great level to track storm systems as they develop and move across North America:
There are a few features, on the map above, that I would like to point out. First of all, the jet stream and overall flow continue to weaken as summer approaches. The jet stream (strongest winds aloft) is actually created by the temperature contrasts that form. This is why the jet stream is at its strongest in January and February, but now as we move through June, the cold air masses have lost their punch, so the heights continue to rise and the jet stream weakens, retreating northward to where the temperature contrasts exist. As this happens, and the heights rise, it is time to look for the summer anticyclone. An anticyclone is a high pressure area, or the opposite of a cyclone (storm system or any low pressure area). There is an anticyclone at 500 mb over the southeastern United States and has been responsible for the June heatwave in the east. A storm, the upper low near the US/Canada border, is very slowly moving east and has a trough aloft that extends into the southwestern United States. The southwest US is where the summer anticyclone will want to be most often because of the heat that develops over the deserts. Eventually, as the jet stream lifts north and continues to weaken, the southwestern Anticyclone will appear and be tough to move out, but not yet, with this pattern we are in right now. And, with this year's LRC, we are expecting some active northwest flow stormy set-ups with possible repeat complex's of thunderstorms that could continue to increase the flooding threat during the next few weeks, even as summer attempts to settle in.
A storm is being generated at the surface by the weather pattern that exists aloft. Look below at the GFS surface forecast for Thursday evening:
There is a lot going on in the above surface forecast. The first thing to notice is a weakening cold front slowing down and stalling just south of Kansas City. This will likely be the focusing mechanism for thunderstorm development Thursday into Friday, before the front sags out of our area leaving us with a nice weekend.
At this time of the year, the fronts get weaker and weaker. And, the humidity, eventually, will no longer get wiped out and pushed away. This is one of the reasons we had enough low level moisture left over for Monday evenings severe thunderstorms that fell apart just north of Kansas City at 11 PM last night. It was quite a lightning show before it fell apart. My point is, though, that the dewpoints are not getting wiped out, despite this front being south of us. Notice the light winds over Nebraska and Iowa. This is holding the high dewpoints in and setting our local area up for another potential heavy rain event. Look below at the dewpoint forecast for Thursday evening:
The GFS is forecast 77 to 78 degree dewpoints pooling along the stalling front just southwest and northeast of Kansas City, as you can see above. A series of weak waves can be seen in the 500 mb flow on the first map above. As these move across thunderstorms will likely develop and organize into one or two MCS's. So, there is potential, again for a lot of rain. This is becoming a bigger concern as the rain keeps falling near the Missouri and Mississippi Rivers and surrounding resevoirs. Below, you can see the rainfall forecast from the NAM and GFS models from last night:
How will this all set up? How much rain will fall? Who will end up with too much rain and flooding? Will there be severe thunderstorms? And, who will get the lowest amounts of rainfall? We will be working on these questions and many more on NBC Action News tonight. Be sure to watch, and we will also try to answer your questions in the blog as well.
Gary