There’s a big severe weather outbreak still underway this weekend. At least one Iowa town was flattened yesterday with 31 tornadoes reported overall. Today it’s ‘only’ six. The evening is young.
Three Four tornado watches and one severe thunderstorm watch are up as I type.
The prevailing wisdom is tornadoes form during a clash between warm moist and cool dry air. That’s a situation likely to exist in the Midwest every spring.
However, if you listen to the experts from the Storm Prediction Center you’ll see there’s more. Tech stuff first. I’ll translate after you read it.
SCATTERED VIGOROUS STORMS ARE ONGOING…FROM NEAR THE DEEP SURFACE CYCLONE CENTER MIGRATING ACROSS NORTHWEST WISCONSIN…SOUTHWARD TO THE VICINITY OF A 90 KT SOUTHWESTERLY 500 MB JET AXIS ACROSS SOUTHWEST WISCONSIN. AN EMBEDDED SPEED MAXIMUM IS IN THE PROCESS OF NOSING ACROSS THE UPPER MISSISSIPPI VALLEY TOWARD THE UPPER GREAT LAKES REGION…WITH A REGION OF ENHANCED UPPER DIVERGENCE CONTRIBUTING TO CONVECTIVE DEVELOPMENT.
- Deep surface cyclone is a low pressure system at ground level.
- 90 kt southwesterly 500mb jet axis means there’s a wind blowing between 110-115 mph at approximately 18,000 feet. The exact height isn’t important.
- Enhanced upper divergence means as the wind is moving by it’s spreading out.
- Convective development means thunderstorms born of air moving upward in the atmosphere
In a thunderstorm parcels of relatively warm air rise into a colder atmosphere. Like a hot air balloon as long as the parcels remain warmer than their surroundings they’ll continue to rise. As described by SPC the Midwest has an added feature this weekend–the jet!
A strong jet streak will help rising air ascend even faster and make the situation much more volatile. Divergence means additional air will need to be sucked up from below to fill an increasingly large atmospheric void. It’s a scary and vicious cycle.
The good news is this severe weather is exceptionally well forecast. It’s tough to believe anyone in the bullseye doesn’t know what’s going on.
The bad news is sometimes there’s just nowhere to hide.