Heat Bursts Across Nebraska

[Cstok]

Anyone experience this the other night?

http://www.crh.noaa.gov/crnews/display_sto...d=2841&source=0

 

[B Ozanne]

I just read about that on the Drudgereport. That must be interesting to be lying in bed at 4am with 70 degree temps only to wake up an hour later with temps in the 90's.

 

[Lori Meyer]

I experienced heat burts in OKC back in 1996... or so. I was in high school at the time and was facinated with the experience. It was the craziest thing at the time and I so badly wanted an explanation. I later saw on the news the term was heat burst; however, no in depth explanation was presented about it. The skies above had a green tint; although there was no hail or preciptation. We were there for a softball tournament and the umpires actually had to call time out for a couple of the heat bursts because the winds were kicking up so much dirt all at once. Glad to finally have an explanation for the term.

 

[Jonathan Whitehead]

Ok so how bout a meteorological explanation to what exactly a heat burst is and what causes it versus a downburst, which i know occurs when a storm collapses and, as a result, brings down to the surface cool air from the mid levels.

 

[Michael P. Morris]

Simple explanation - consider a saturated parcel in the midlevels of the storm. As cool, dry air gets entrained from outside the storm (typically by turbulence) the water vapor evaporates, cooling the parcel and making it negatively buoyant (since it is cooler than the surrounding environment). The sinking air then warms adiabatically by compression as it descends toward the surface.

http://www.theweatherprediction.com/habyhints/341/

 

[B Ozanne]

I was thinking. It's kind of like an overshooting cloud top.

A negatively bouyant parcel has so much downward momentum it shoots past its equilibrium temperature and continues to the surface. Naturally, it should stop when the temps are equal, but it has momentum and continnues to the surface.

 

[Jeff Snyder]

I was thinking. It's kind of like an overshooting cloud top.

A negatively bouyant parcel has so much downward momentum it shoots past its equilibrium temperature and continues to the surface. Naturally, it should stop when the temps are equal, but it has momentum and continnues to the surface.
[/b]

And remember that buoyancy is force, which means that buoyancy acts to ACCELERATE parcels (we'll neglect other complications like VPPGF, water loading, turbulence, etc). So, as long as the parcel is more dense than the surroundings, it will actually continue to accelerate downward. Therefore, it should always take some time to bring it's velocity back to 0m/s given that positive buoyancy must act to provide positive acceleration (meaning to slow the parcel's downward ascent before beginning to move the parcel "upward").

In an ideal situation, therefore, a parcel should "overshoot" the tropopause to a height at which the negative buoyancy (CINH ABOVE the equilibrium level) equals the positive buoyancy (CAPE). Of course, for updrafts which have an EQ near the tropopause, there tend to be other factors which affect vertical acceleration (e.g water loading, entrainment/detrainment, turbulence, etc). So, ideally and where buoyancy is the force considered, you should be able to find the height of an overshooting top based on the sounding... A parcel moving upward through a profile with 5000 j/kg CAPE should not reach 0 m/s (i.e. should not stop moving upward) until the parcel has ascended through 5000j/kg CINH (or -5000 j/kg CAPE if you wish). To "stop" a downward moving parcel is similar to "stopping" an overshooting top, just occurring near the ground (where there's a stable layer / inversion) rather than at and above the tropopause (where there's also an inversion).

 

[mrobinett]

Nah, youre all wrong, its global warming, wheres my grant money?!?!?

That is interesting, guys!!