Dry line strategy...

[Andrea Griffa]

Hi all, I 'd like to discuss about chasing dryline strategies. Before to chase a dryline all the chasers think if it's better to go on the triple point, where, if the termodynamic and kinematic setup is good, you could have high probabilities of tornadoes formation, or go southward where the possibility of tornado is maybe a little minor but probably storms will be more isolated and more chaseable. I think this is a dilemma that is quite frequent in chasers.

I take you some examples:

@
http://www.spc.noaa.gov/exper/archive/even...30515/rad28.gif
http://www.spc.noaa.gov/exper/archive/even.../hpc-sfc-00.gif

This case is taken from the outbreak of may 15th 2003: you can see that on the triple point there's some severe storms but the best storms to chase at that moment are more southward. Tornadic activity did occur in both regions(Northward and Southward) but southern supercells did remain more isolated.

@
http://www.spc.noaa.gov/exper/archive/even...50511/rad29.gif

http://www.spc.noaa.gov/exper/archive/even.../hpc-sfc-03.gif


This case is taken from may 11th 2005. As you see just ahead of the low pressure at the intersection between dry line and warm front there are some severe storms; I remember in that region convection did start quite early in the afternoon. More southward Cap was further strong and did hold out till 8.30 pm as isolated dry line supercells started to form. A lot of chasers thought that nothing could have developed. In the first region the spread convective development didn't take to an isolated supercellular convection(I saw supercellular structures but no tornadoes). SPC reported some brief tornadoes but I think they were sheriffnadoes or something like that.
In the second region, at about 1.45-2.00Z some supercells did form and produced some cool tornadoes(Ulysses night tornado).

@
http://www.spc.noaa.gov/exper/archive/even.../hpc-sfc-03.gif

http://www.spc.noaa.gov/exper/archive/even...50611/rad27.gif

On June 11th 2005 if you would have gone too much southward probably you would have seen anything good: maybe you would have found just some hail stone but nothing else.


So wich of the two kinds of chasing drylines ways do you generally prefer? Write down your experiences and explain why.

 

[Bob Schafer]

(gf) Floss and I chased the TP 030515. As I recall, and this is purely from memory, I chose that target late in the day due to better mid and upper level support at the TP vs DL. Seems there were some good, stiff 700 and 500mb winds (for ventilation), and better directional shear at initiation near Clayton (CAO) vs further south.

I may well have not done that if Td's were not also there, but they were. Often, Td's up around CAO, at around 5000 feet, will be only in the upper 40's or low 50's, and LCL's will be just a little too high. Mid-50's Td's are fine there for chasing, but on 030515, I believe the CAO Td was in the lower 60's, and they were even higher as the storms that initiated migrated into deep moisture to the ENE.

Actually, CAO was probably in some slightly drier sfc air directly bullseyed in the low, but you get the point...

This is a great question, though, and a question that plays out time and again on chase day. TP or DL? TP or DL??

Where's the best combination of instability, deep moisture, upper level support? What about the cap? Is it too strong somewhere? Too weak? What about convective debris from last night? What about insolation and stratus deck? Where are there good roads? Are there trees and/or hills in one target vs another (and where the storm motions will take them)? Will there be a chaser circus in one spot and not another? Where is tomorrow's target? Will one target today leave me strapped to reach tomorrow's?

Everything has to be considered, and these are only about half of the questions. Usually, some answers are easy and others hard, but they're never the same answers day-to-day. It's all part of the fun!

Bob

 

[Dan Robinson]

I'm becoming a fan of dryline bulges. If you can get a storm to go up on the nose of the bulge, it usually will not have problems with upstream convection to the south fouling the inflow. A bulge just south of the surface low (where directional shear/backed winds are not maximized but still decent) can be a very good thing.

 

[Brian Stertz]

Yeah dryline bulge supercells can be pretty exciting stuff to chase...especially when there is a good strong cap to the south to hold any competition down for the inflow. Have seen some nice events when mesolows are also a factor. Lately, I have been really attracted to the warm front and triple point type setups though. It seems that as of late, the dryline has been staying majorly hell-capped.

 

[Andrea Griffa]

Originally posted by Bob Schafer
(gf) Floss and I chased the TP 030515. As I recall, and this is purely from memory, I chose that target late in the day due to better mid and upper level support at the TP vs DL. Seems there were some good, stiff 700 and 500mb winds (for ventilation), and better directional shear at initiation near Clayton (CAO) vs further south.

I may well have not done that if Td's were not also there, but they were. Often, Td's up around CAO, at around 5000 feet, will be only in the upper 40's or low 50's, and LCL's will be just a little too high. Mid-50's Td's are fine there for chasing, but on 030515, I believe the CAO Td was in the lower 60's, and they were even higher as the storms that initiated migrated into deep moisture to the ENE.

Actually, CAO was probably in some slightly drier sfc air directly bullseyed in the low, but you get the point...

This is a great question, though, and a question that plays out time and again on chase day. TP or DL? TP or DL??

Where's the best combination of instability, deep moisture, upper level support? What about the cap? Is it too strong somewhere? Too weak? What about convective debris from last night? What about insolation and stratus deck? Where are there good roads? Are there trees and/or hills in one target vs another (and where the storm motions will take them)? Will there be a chaser circus in one spot and not another? Where is tomorrow's target? Will one target today leave me strapped to reach tomorrow's?

Everything has to be considered, and these are only about half of the questions. Usually, some answers are easy and others hard, but they're never the same answers day-to-day. It's all part of the fun!

Bob

Bob, cool considerations! :wink: I completely agree with your post.

Dan, I'm a fan of dry line bulge too: it's terribly true that it's a really nice option when bulge is just south of the surface low. Low level convergence and shear is enhanced along the bulge and it could help to break the cap.
Jon Davies did a study about a double dryline, both with a bulge; the tornadic supercell developed just ahead of the bulge and in the low zone of that.

Taken from jon Davies's site http://members.cox.net/jdavies1/

 

[Bob Schafer]

Mulvane! For newbies only, LOL, here's what happened that day:

http://community.webshots.com/photo/515456...155371428zIZHqw

 

[mikegeukes]

DRYLINE MAGIC by Tim Marshall
http://www.stormtrack.org/library/forecast/dryline.htm

Mike

 

[samuel stone]

I will always remember the mulvane tornado not only for its beauty and being very close to home, but because it was my frist tronado. It was very satisfiyng how I nailed the forcast since just a couple weeks before I completely blew the may 29th outbreak.

As far as the dryline goes I also like the bulge as a general rule but it All depends on how the mesoscale picture sets up on that paticular day.

 

[Dan Robinson]

Yes when I think of a good DL bulge day, I think of Mulvane.

 

[Shane Adams]

May 12, 2004 wasn't a bad DL buldge day either.

 

[Jeff Snyder]

Originally posted by Shane Adams
May 12, 2004 wasn't a bad DL buldge day either.

That's the date that first came into my mind when I read this thread.