Topic: Pyrocumulous severe storms?

[nmoir]

Hi guys , has anyone seen a fire initiated storm become severe or does as the haines index indicates the level of stability in the atmosphere prevent such events?
i know that the canberra fire created updraft powerful enough for lightning (though the pix of these are fake i think) and i saw evidence of extreme winds at the surface which forced metal poles to the ground (pic included) but i think these were localised to the fire event.
included is a pic of pyrocumulous over lake burragorang a few weeks ago , this produced a couple of showers.
 it would be interesting as it would be possible to get a life cycle between storm , lightning, fire, pyrocumulous, storm , lightning, fire

[Jimmy Deguara]

Hi Nick,

The problem here is how much can be attributed to the fire and how can it be tested? The same argument can be used for cloud seeding. The test in my opinion is that if there were other cumulus clusters around and none broke the cap or developed into storms throught the period, and the storm developed from pyrocumulus then yes, there would be more confidence in the fire having some influence.

I do recall Paul Graham sugegesting that there was a documented supercell in Victoria that developed from a bushfire. Paul?

Regards,

Jimmy Deguara

[Jeremy Lunn]

Weren't there also whole forests that were flattened just before the fires came through in Canberra?  It was as though the extreme heat of the extreme heat of the fire had somehow created a strong gust ahead of the fire front.  I think it was also evident that the trees hadn't been flattened during the fire itself as the undersides of the fallen logs hadn't been burnt.  I don't know much about fire behaviour though, this was just something I had seen on the ABC in a doco.  It seemed that even the experts were baffled by this phenomenon.

[Jimmy Deguara]

Jeremy,

Welcome to the forum. I would not be surprised if the Canberra damage referred to by Nick above were fire tornadoes known as fire devils that tend to spin up along the fire fronts. However, I have also observed footage of a landspoout type of tornado in Colorado bushfires a few years ago! This developed on the southern side of the plume - pyrocumulonimbus. This makes an interesting comparison considering that pine forests existed in the vicinity of the suburbs affected by bushfires in the Canberra case.

Regards,

Jimmy Deguara

[Michael Thomas]

Today in Victoria there was an interesting echo just NW of Mt Buller that persisted for about 5 hrs. The fact that the echo was stationary for the entire 5 hrs suggests that it was the result of a bushfire however the reflectivities were at times quite intense, far stronger than any I have previously seen from fires. Steep low/mid level lapse rates were present in much of Victora with sufficient lower level moisture for storms. I can only guess that a fire initiated a storm which effectively 'back built' though its duration to remain stationary unlike other cells on the day.

I'd be interested to hear others opinions.

MB EDIT - Permanent radar loop added:
http://australiasevereweather.com/storm_news/2007/radar/20070116/melbourne256.htm

Michael

[Jimmy Deguara]

John,

That certianly is interesting given other storms were moving SSE. I think that that is a fire with pyrocumulus or pyrocumulonimbus regenerating from the fire. It may have dropped precipitation as well.

(Just a note, please let Michael Bath know about these radar links from strike one given they only last 2 weeks and the link becomes dead. Michael will always being willing to place permanent links. That then validates the post).

Regards,

[Paul Graham]

Jimmy, I can't remember the event you referred to.  What I would say on this topic is that unless the synoptic scale environment can sustain a severe storm, given factors such as CAPE and wind shear, then any storm triggered by a bushfire would be unlikely to remain severe if in fact it was severe while over the bushfire zone.  A bushfire can trigger a storm but cannot sustain it outside of the area where the fire is burning.  For a storm to be sustained, it needs to develop in the right synoptic scale environment (CAPE, wind shear etc...).  But if the synoptic scale environmental conditions are favourable then a fire is not the only way a storm can be triggered.  Fronts, convergence lines, elevated terrain and sea breezes all provide the necessary lifting mechanism for a storm to develop.  Maybe if there is a strong enough cap to inhibit lifting by way of some of these mechanisms, a large enough bushfire could provide enough thermal lifting energy for initiation.