Severe Weather Chances on the Way
FAYETTEVILLE, Ark. (KNWA/KFTA) — Recently, we’ve had spring-like temperatures, which is nice and all, but that comes at the price of spring-like storms.
We’re currently monitoring the chance for severe weather Tuesday-Wednesday. We’re quite a few days out, so there’s still time for the system to evolve and models to change back and forth on the small-scale detail, but that big picture looks to be trouble.
What makes this look troubling? I’ll answer that here in the latest Weather Blog!
Jet Stream
The jet stream is a river of air about 35,000 feet above the ground. It helps shape the general weather pattern. Just like a river, it has waves which are troughs and ridges, think of it as mountains and valleys.
Here is the jet stream forecasted for Tuesday late afternoon/early evening. There is a trough over the western part of the United States. The dashed line is called the trough axis. This divides the trough in half which is important for later. Over the Appalachians, there is a ridge and dividing that is a zigzagged line called the ridge axis. We’re focused on the trough for severe weather potential.
This is the type of motion associated with the trough. Since it’s going counterclockwise we call this cyclonic flow. Downstream or on the right side of the trough axis, we see rising motion. Now for a ridge, we have to look at the anti-cyclonic flow pattern or clockwise motion.
Upstream of the ridge is also where we see rising motion. Putting this all together, we can get a general area to expect storm system development.
Looking at that polygon for a storm system to develop we need to divide this area, which we call a jet streak, into 4 quadrants kind of like dividing a trough and ridge.
Pretend this is tilted at about 30° up on the right side, then you have the right idea for the jet streak forecasted for Tuesday. Section 1 is called the left entrance. Section 2 is called the right entrance. Section 3 is the left exit. Section 4 is called the right exit. In the right entrance (2) and the left exit (3) that’s where you have rising motion. In the left entrance (1) and the right exit (4) we will see a sinking motion.
Technically our area is in the right exit, which would mean no upward motion meaning no storms, right? Not exactly. If the area downstream of a trough or upstream of a ridge is strong enough, then it doesn’t matter as much, but the green regions will see stronger lift and the red regions will see not as strong of lift.
In summary, the jet stream pattern is favorable for strong upward motion, which could lead to a strong storm system. For other details, we need to look at what the surface could look like.
Moisture
For storms to grow, you need moisture. We will have plenty of moisture, but why and where is it coming from?
To answer this we go to the mid-levels of the atmosphere. This is about 5-15 thousand feet above the ground. We’ll be getting most of that warm moisture from the Pacific Ocean near the Baja Peninsula. We often refer to this moisture transport and energy flow as a Baja Blast.
We’ll also be getting moisture from the Gulf of Mexico thanks to a surface low-pressure area to our west and a high-pressure area to our east.
These two areas are going to funnel in a lot of warm moist air at the surface.
What can we conclude?
The jet stream and moisture are the two biggest components to look at in a forecast this far out because this seems to give us a sign that there will be a lot of lift. Currently, we think we could see this system develop some pretty strong storms over our area. We’re not the only ones who think so. The Storm Prediction Center issued a Day 6 Severe Weather Outlook with our entire coverage area.
We’ll continue to keep you updated in our newscasts and on social media as we get closer.
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