OFB's - Longevity

[John Hudson]

I know the interaction of updrafts with outflow boundaries has been well-documented in the production of tornadic storms in otherwise unfavorable wind fields, but what I'd like to know is just how long can OFB's persist?

It must depend on the scale/intensity of the convection that produced it, but in some of your experiences, what have been some of the longer lived OFB's that you've observed?

Many thanks in advance for your examples!


John

 

[Terry Tyler]

well, john..im afraid i cant remember any good days off the top of my head, but i will tell you this...its not uncommon for OFB's to last a long time...in some cases, they can stick around for a day or better...

if you watch the radars some nights after a big thunderstorm complex goes by, you can see the OFBs doing their thing...in my experience with them, ive seen em travel out away from the storms, and then kinda stall out and set the stage for storms the next day...

as far as the relationship between the storms downdraft and the life of the outflow boundary, i cant say for sure...but i would suggest that a stronger downdraft would make for more a enhanced outflow boundary, and also something to note the landscape can effect them, how far they travel and whatnot...

just a few things i know about em...sorry if i couldent help more!

 

[Ed Schoenborn]

What is an OFB? What does the abbreviation stand for.?

 

[Josh Richardson]

What is an OFB? What does the abbreviation stand for.?

Outflow boundary....

 

[Brandon Ivey]

John, I would say that outflow boundaries could last anywhere from a few hours up to 24 hours in time. You can have really small outflow boundaries/gust fronts that develop from a single thunderstorm. This can create other storms and even brief tornadoes as other storms interact with this feature. The outflow boundaries I closely monitor are the large boundaries that are produced from overnight convection. These are the wonderful tools that can help produce a cyclic tornadic supercell the following day if the storm motions are parallel to the boundary. Some personal examples are June 23rd, 2002 in Brown County, SD and just this year on the May 24th supercell in central OK. I have had good luck catching tornadoes along outflow boundaries over the past couple of years. Even if the storm is crossing the boundary into more stable surface conditions, it will have a limited window of opprotunity to produce a brief tornado or two before it becomes too elevated in the stable boundary layer air. I hope this helps some. If you plan to chase outflow boundaries, just like warm fronts, sit along the boundary or just to the north of it by 10-30 miles. I try to stay somewhat north of it. Your tornado season is about to begin! Good Luck chasing! I have a passport this year but not much vacation time left....darn.

 

[Bill Schintler]

RE: Long-lasting OFBs

Have a look at Friday, May 21, 2004...
http://www.spc.noaa.gov/climo/reports/040521_rpts.html

This was one of several days in a very active period - the Hallam tornado was the following evening. On May 21, a large morning MCS had pushed a strong outflow boundary south to roughly a Washington, IA to Waterloo, IA line by early afternoon. The surface flow was strongly backed north and east of this boundary, while by mid-afternoon, the airmass had recovered in the cool sector. Storms initiated near Waterloo, and then developed and tracked south and east along the OFB, with several tornadic HP supercells as storms tracked along the boundary and had backed surface inflow.

Tomorrow, OFBs will play a key role in the evolution of severe storms in extreme northeast KS. An ongoing MCS is now tracking E through NEB, while an other area of convection in western KS is weakening. Meanwhile, the LLJ is focusing further east into south and southeastern NEB, with convection rapidly developing there in a zone of isentropic upglide along 310-340K surfaces. All of the Nebraska convection will eventually merge into one convective system, while the Kansas storms will eventually dissipate. By tomorrow morning, a large MCS will be underway in southeastern NEB, and this will produce a significant and long-lasting OFB, most likely located somewhere between I-70 in ERN KS and the KS/NEB border by mid-afternoon. This will be the focus for surface-based convection by early evening. Deep-layer shear will be marginal, however large hodograph curvatures and directional shear should exist from the surface up to about 4 km, which will enhance chances for rotating updrafts and tornadogenesis.

- bill