It's been pretty hot and dry around Denver lately! Looks like we've got a chance for some supercell thunderstorms and severe weather tomorrow, (Tuesday July 10). I'm going to keep an eye on things and may head out in my Dodge Ram chase vehicle to check things out after work tomorrow.
Yesterday's (Sunday July 8) storm activity was somewhat severe, but not really "chaseable". In storm-chasing circles, we look for "supercells" which have a very specific structure and properties that set them apart from ordinary thunderstorms. Their radar signature, look and "feel" are quite different from "air mass" thunderstorms. When we chase, supercells are the Holy Grail we seek. Yesterday's activity was "pulse" in nature. Every thunderstorm has an updraft and a downdraft. With pulse-severe storms, the updrafts and downdrafts are not in syn ch, meaning that one is intense while the other is weak. The storm oscillates and can generate brief severe weather, but it quickly dies as the mechanics interfere with one another. Pulse severe storms are not chaseable because by the time we get to the storm, it has usually weakened or dissipated.
Supercells are another matter entirely! Their updrafts and downdrafts are oriented in such a way that they work together to feed and ventilate the storm. Supercells can last for hours and generate incredibly severe weather. This includes large hail, winds in excess of 60 mph, deadly lightning and tornadoes. Stormchasers look for chase environments conducive to supercell development. For any thunderstorm, you need moisture, heat, lift and instability. For supercells, the additional ingredient of "shear" is needed. Wind shear comes in various forms. At the basic level, there's "speed" shear and "directional" shear. Speed shear is an increase of wind speed with height. Directional sheer is a "veering" of wind with height. Ideally, that would mean winds from the southeast at the surface, south or southwest at the mid-levels and west higher up. This give a spin to the thunderstorms and causes their updrafts to be separated from the downdrafts so they don't interfere. This way, the storm can sustain itself, sometimes for many hours.
That's the long explanation of why I didn't go chasing yesterday! The photo you see with this post is of a "classic" supercell, taken by my friend Helen Kelly. She was with us on Tour 7 this year and took this shot in northern Nebraska. This storm has just blown through the cap and exploded into a supercell in less than 30 minutes! Click HERE for a link to her photo albums from our chase!
Yesterday's (Sunday July 8) storm activity was somewhat severe, but not really "chaseable". In storm-chasing circles, we look for "supercells" which have a very specific structure and properties that set them apart from ordinary thunderstorms. Their radar signature, look and "feel" are quite different from "air mass" thunderstorms. When we chase, supercells are the Holy Grail we seek. Yesterday's activity was "pulse" in nature. Every thunderstorm has an updraft and a downdraft. With pulse-severe storms, the updrafts and downdrafts are not in syn ch, meaning that one is intense while the other is weak. The storm oscillates and can generate brief severe weather, but it quickly dies as the mechanics interfere with one another. Pulse severe storms are not chaseable because by the time we get to the storm, it has usually weakened or dissipated.
Supercells are another matter entirely! Their updrafts and downdrafts are oriented in such a way that they work together to feed and ventilate the storm. Supercells can last for hours and generate incredibly severe weather. This includes large hail, winds in excess of 60 mph, deadly lightning and tornadoes. Stormchasers look for chase environments conducive to supercell development. For any thunderstorm, you need moisture, heat, lift and instability. For supercells, the additional ingredient of "shear" is needed. Wind shear comes in various forms. At the basic level, there's "speed" shear and "directional" shear. Speed shear is an increase of wind speed with height. Directional sheer is a "veering" of wind with height. Ideally, that would mean winds from the southeast at the surface, south or southwest at the mid-levels and west higher up. This give a spin to the thunderstorms and causes their updrafts to be separated from the downdrafts so they don't interfere. This way, the storm can sustain itself, sometimes for many hours.
That's the long explanation of why I didn't go chasing yesterday! The photo you see with this post is of a "classic" supercell, taken by my friend Helen Kelly. She was with us on Tour 7 this year and took this shot in northern Nebraska. This storm has just blown through the cap and exploded into a supercell in less than 30 minutes! Click HERE for a link to her photo albums from our chase!
