Fred Gossage
EF1
(Why our current system wasn't as synoptically favorable as thought)
After tracking what appeared, at the synoptic scale, a potentially high-end type severe weather threat for over a week... and then watching it, for the most part, go up in flames for the same reasons as a recent similar bust.... I decided to do some digging into synoptic patterns associated with our past BIG tornado days....and also events that looked very significant, but ended up busting. While the main reason this threat did not reach its full potential is the continued convection along the coast blocking the unstable air from coming north, when looking for true reasons to learn from, it's not as simple as that. We must look into why that could've happened? Has it happened before? What makes this event different from all the big-league events that we HAVE faced in the past? First, I'm going to generally dissect the synoptic pattern evolution of this system that we're dealing with:
In the first image, you see our initial wave from back on Monday and Tuesday lifting northeast into the Great Lakes, with the surface front shifting southeast into the Mississippi Valley. Also note another trough off the northeast coast... and how amplified the western North Atlantic is in the mid/upper levels. Meanwhile, we have the bigger disturbance approaching the northwest coast of the United States.
We advance time forward into the midweek timeframe. We see that the initial wave has ejected out to the east and northeast, but left a mean trough over the center of the nation, and the bigger impulse is diving across the Rockies toward that remnant trough. Height falls are starting to spread southeastward, and in response, a surface low is starting to form over western Texas. Note that the mid/upper-level jet is mostly parallel to the front that is along the coast...and because of this, the front is stalled near the coast.
By the time the system ejects into the Plains, because of the upper-level flow generally remaining parallel to the surface front until the actual system ejects out the day of the event, the surface front has remained stalled near the coast. This has kept low-level convergence near the coast, juxtaposed with what turned out to be several impulses embedded in the subtropical jet, which initiated complex after complex along that surface front, which reinforced it and REALLY delayed it from coming northward.
Below, I will outline how the synoptic evolution of most of our BIG events in history have played out.
Already, to start out with, you can already see significant differences before the main impulse even digs into the western United States. Note that there is a ridge off the Atlantic coast, and the western North Atlantic is much less blocked. This allows the lead storm system over the eastern United States to eject more east-northeastward with a flat ridge building in behind it over the middle of the nation. Note that the front has already stopped along the coast, as the upper-level flow goes parallel. Note that because of the more west to east ejection of the lead impulse and a weak ridge over the center of the nation, the second disturbance is actually diving southeastward into the California coast.
We advance further in time, and the lead disturbance is well out of the way now, with a low-amplitude ridge over the southeast. The second disturbance has carved out a trough in the Four Corners, further southwest than the system we've dealt with...and ahead of that, southwest flow aloft (at more of an angle with the surface front) and height falls already overspreading the High Plains well ahead of the system....has already caused the surface front to move away from the coast a good day or two ahead of the event. This allows the low-level convergence source to move away from the coastline while the coast is still capped under shortwave ridging, before any possible subtropical jet impulses arrive.
We now advance to the day of the hypothetical event, and you can see that the warm front has been allowed to progress significantly northward. Now, there is a large, broad warm sector well inland ahead of a major storm system ejecting into the middle of the nation....and a synoptically evident tornado outbreak setup is on the maps.
Big events can still happen with the synoptic evolution described in Scenario One. Once such MAJOR event that comes to mind is November 21-23, 1992...with many tornadoes (several of F4 intensity) from Texas eastward to the Carolinas and northward into the Ohio Valley. There is one significant difference with that event though. The lead wave ejected more northward across the Plains, with a stronger ridge in the Southeast, and this allowed the lead system to dive in a little further west...with the upper-level flow ahead of it more perpendicular to the front, allowing it to come northward earlier.
Just about all the other BIG tornado days in history that we think of (Palm Sunday 1965, Super Outbreak of 1974, Delta Outbreak of February 21 1971, May 18 1995, April 8 1998, April 26 1991 in the Plains, May 3 1999 in the Plains, November 10 2002, May 4 2003, April 7 2006, March 1 2007, and Super Tuesday 2008) all happened like the synoptic evolution described in Scenario Two.
It seems that it's very important, for a high-end severe weather event, that the western Atlantic is not blocked, so that any lead impulse can eject more eastward... with ridging building in behind it ahead of the bigger impulse. The southwest flow aloft overtop the more west-to-east surface front along the coast, and height falls over the Plains well ahead of the upper trough to allow return flow to intensify well ahead of the storm system is very crucial in getting the front off the coastline before upper-level support arrives and spawns convective complexes along the coast. I feel that this information will help us know which systems to really key in on in the medium range.... for a higher threat of a high-end type event having a better chance to verify, versus the systems that still have potential......but have a much higher bust potential.
After tracking what appeared, at the synoptic scale, a potentially high-end type severe weather threat for over a week... and then watching it, for the most part, go up in flames for the same reasons as a recent similar bust.... I decided to do some digging into synoptic patterns associated with our past BIG tornado days....and also events that looked very significant, but ended up busting. While the main reason this threat did not reach its full potential is the continued convection along the coast blocking the unstable air from coming north, when looking for true reasons to learn from, it's not as simple as that. We must look into why that could've happened? Has it happened before? What makes this event different from all the big-league events that we HAVE faced in the past? First, I'm going to generally dissect the synoptic pattern evolution of this system that we're dealing with:
In the first image, you see our initial wave from back on Monday and Tuesday lifting northeast into the Great Lakes, with the surface front shifting southeast into the Mississippi Valley. Also note another trough off the northeast coast... and how amplified the western North Atlantic is in the mid/upper levels. Meanwhile, we have the bigger disturbance approaching the northwest coast of the United States.
We advance time forward into the midweek timeframe. We see that the initial wave has ejected out to the east and northeast, but left a mean trough over the center of the nation, and the bigger impulse is diving across the Rockies toward that remnant trough. Height falls are starting to spread southeastward, and in response, a surface low is starting to form over western Texas. Note that the mid/upper-level jet is mostly parallel to the front that is along the coast...and because of this, the front is stalled near the coast.
By the time the system ejects into the Plains, because of the upper-level flow generally remaining parallel to the surface front until the actual system ejects out the day of the event, the surface front has remained stalled near the coast. This has kept low-level convergence near the coast, juxtaposed with what turned out to be several impulses embedded in the subtropical jet, which initiated complex after complex along that surface front, which reinforced it and REALLY delayed it from coming northward.
Below, I will outline how the synoptic evolution of most of our BIG events in history have played out.
Already, to start out with, you can already see significant differences before the main impulse even digs into the western United States. Note that there is a ridge off the Atlantic coast, and the western North Atlantic is much less blocked. This allows the lead storm system over the eastern United States to eject more east-northeastward with a flat ridge building in behind it over the middle of the nation. Note that the front has already stopped along the coast, as the upper-level flow goes parallel. Note that because of the more west to east ejection of the lead impulse and a weak ridge over the center of the nation, the second disturbance is actually diving southeastward into the California coast.
We advance further in time, and the lead disturbance is well out of the way now, with a low-amplitude ridge over the southeast. The second disturbance has carved out a trough in the Four Corners, further southwest than the system we've dealt with...and ahead of that, southwest flow aloft (at more of an angle with the surface front) and height falls already overspreading the High Plains well ahead of the system....has already caused the surface front to move away from the coast a good day or two ahead of the event. This allows the low-level convergence source to move away from the coastline while the coast is still capped under shortwave ridging, before any possible subtropical jet impulses arrive.
We now advance to the day of the hypothetical event, and you can see that the warm front has been allowed to progress significantly northward. Now, there is a large, broad warm sector well inland ahead of a major storm system ejecting into the middle of the nation....and a synoptically evident tornado outbreak setup is on the maps.
Big events can still happen with the synoptic evolution described in Scenario One. Once such MAJOR event that comes to mind is November 21-23, 1992...with many tornadoes (several of F4 intensity) from Texas eastward to the Carolinas and northward into the Ohio Valley. There is one significant difference with that event though. The lead wave ejected more northward across the Plains, with a stronger ridge in the Southeast, and this allowed the lead system to dive in a little further west...with the upper-level flow ahead of it more perpendicular to the front, allowing it to come northward earlier.
Just about all the other BIG tornado days in history that we think of (Palm Sunday 1965, Super Outbreak of 1974, Delta Outbreak of February 21 1971, May 18 1995, April 8 1998, April 26 1991 in the Plains, May 3 1999 in the Plains, November 10 2002, May 4 2003, April 7 2006, March 1 2007, and Super Tuesday 2008) all happened like the synoptic evolution described in Scenario Two.
It seems that it's very important, for a high-end severe weather event, that the western Atlantic is not blocked, so that any lead impulse can eject more eastward... with ridging building in behind it ahead of the bigger impulse. The southwest flow aloft overtop the more west-to-east surface front along the coast, and height falls over the Plains well ahead of the upper trough to allow return flow to intensify well ahead of the storm system is very crucial in getting the front off the coastline before upper-level support arrives and spawns convective complexes along the coast. I feel that this information will help us know which systems to really key in on in the medium range.... for a higher threat of a high-end type event having a better chance to verify, versus the systems that still have potential......but have a much higher bust potential.
