Topic: Cold inflow killing the storm

[Dave Nelson]

ok  next topic 

 Over the recent years since I have got into storms and chasing,  I have often noticed how good active
cells coming down off the mountains and over the Sydney basin have died out before or by the time they
reach the coast.
  Now on a number of these times I have seen how there is a good easterly wind bringing in cool air
and lots of low level cloud.   I had concluded that this is the mechanism killing these storms ??
( or at least the main reason)

you may be aware of other factors that I'm not. ?

cheers
Dave N

[Mike]

Thankfully there's someone else out there who is in need of educating - jut like me! 

I can only speak from what storms we get through Darwin - our storms are generated by hot easterly and SE flow, but I have noticed also that when they come within almost to 50km of our area heading to Darwin they get cut-off also by cold air - I'm still learning about the things, but i think i'm right when i mention that the storms need good moist inflow - i guess dependant on the temperature of the air coming in?

 It's probably why the seabreeze kills of a lot of severe storms the develop near Darwin but don't make it, even this far out and yes, i would agree (with my limited knowledge also) that it is all relevant to lattitude winds at the lower, middle and upper and also temperature feeding the systems.

I've observed nice strong updrafted storms coming into Darwin and then within half an hour see them dissipate drastically - with no obvious apparent visual reason - but it's what you CAN'T see that is the answer!  If we all had the laptop with the links to all the Met data with us on the road then we could all be chasing our tails less - but that's half the fun i guess.

Hope i made some sense - but I'm on the same level as you and know where your'e going!

Mike 

[Jimmy Deguara]

Dave and Mike,

Mike the dynamics of Darwin are slightly different than here given the much warmer ocean and different orientation of the land mass compared to the direction of some of the storms.

Dave, you are correct in terms of the sea breeze front being too cool such that most storms crossing the sea breeze front collapse.

Another factor is wind shear. Given that most storms initiate over the ranges, weak wind shear days or days where the mean steering winds are oriented such that the storms do not move off the ranges anyway.

I hope this helps.

(If there any components of the informative posts that puzzle you, feel free to single out this points and ask more questions).

[Mike]

Thanks Jimmy.  That's exactly why i jioined the forum: to find out more about storms!  If you could in layman's terms explain to me the 'structure of tropical storms in darwin' then i would be greatly thankful!  I think sometimes i get a little off-track with some of the characteristics of storms here in Darwin from other parts of Oz, but i think i'm sort of getting there with regard to sea breezes killing or storms - even the met office agrees! But i am thankful that you post your comments, as obviously you have the knowledge and experience to such things. 

I await your description of tropical storms - I have read articles on them, but it's the lingo i'm getting around which may be confusing me.

Mike :}

[Mike]

Okay,  This is for Jimmy or Michael or anyone else who has more informative experience than me to answer my questions!

Given that the majority of our storms up here are pulse storms with the occasional gulf line systems that come through, perhaps a true or false answer could be given with explanations to the following!

(1) Given the topography of the Territory (flat) that most of the storms are generated up to 100km from Darwin are what type of storms?

(2) Are the storms in Darwin generally strong updraft and low wind shear generated?

(3) Because of easterly wind flows during the wet (void of monsoon flow) is the air drier and this is why the storms don't last?

(4) Does the sea breeze from the Arafura Sea kill off our storms?

(5) We have high CAPE but the essential ingredients for strong storms is what?

(6) Is it a just the fact that we have tropical storms that just blow in and we have the occasional conditions for strong severe weather!?

(7) Is the lack of cool are colliding with moist air up here just the reason we dont get supercells?

That's a handfull for you.  I'd appreciate your input fellas.  Look forward to it.

Mike

[Dave Nelson]

Quote Jimmy ... "Another factor is wind shear. Given that most storms initiate over the ranges, weak wind shear days or days where the mean steering winds are oriented such that the storms do not move off the ranges anyway."

  Yes  thats fair comment too, and I observed just within the last few days, umm...  30.12.06,  where the many
small storms did move northwards along the mountains paralleling the coast.

 From now on, on days where good storms die coming off the mountains, and there is NO OBVIOUS easterly
wind and cloud coming in, I will have to see if there are other possible observable reasons for the collapse.

thanks  for responses Jimmy and John


Dave N

[Mike]

Thanks so much John.  You have helped me heaps.  Once i get my head around wind sheer etc then I'll be more up to speed - although i understand what all this means, it's putting it into context to make some sort of meteorological sense!  But you have given me some excellent answers that make a lot more sense now.  I'll just have to keep reading up on it and understanding all the elements that make up storm structure - happens to all of us i suspect and it takes time!

Will copy the answers and stick in my severe weather folder for constant perusual!

[Michael Thomas]

Dave, storms will often die coming off the ranges for a number of reasons 1) As you mentioned they hit cooler air by the coast thanks to a strong sea breeze, this results in a major decrease in CAPE. 2) Often there just may not be enough CAPE for storms by the coast, remember a T/Td of 25/17 at 1000m is roughly equivalent to 35/19 on the coast, ie at sea level. Therefore, given similiar surface temps and moisture, higher CAPE will usually exist over the ranges 3) Capping, sometimes there will be enough CAPE for storms by the coast however if capping is too strong storms will not form. This was the case in SE Qld on Saturday, where the morning sounding had LI of -4 and CAPE of 900 j/kg. Plotting with the afternoon temperature gives an LI of -6 and CAPE of ~2000 j/kg, plenty of CAPE there. However, even at 30C there was significant CIN so no storms resulted by the coast. On the ranges, the cap was easily broken and there were severe storms.

Michael