Forecasting and understanding ULL's

[Cyclonicjunkie]

Ok, so now that we're clear on what we're talking about, what questions do you have about it

Ok what says that there is an ULL there, just the fact that there is a sw trough on 500mb analyisis chart?

Is there any way of trying to predict how these will behave, I mean I know how a surface low SHOULD behave but I have no clue to what drives these west or north or south. Also how are the strength of these measured (Just in vorticity?), or what causes one to strengthen or weaken or even disapate etc.

[am19psu]

Ok what says that there is an ULL there, just the fact that there is a sw trough on 500mb analyisis chart?

Is there any way of trying to predict how these will behave, I mean I know how a surface low SHOULD behave but I have no clue to what drives these west or north or south. Also how are the strength of these measured (Just in vorticity?), or what causes one to strengthen or weaken or even disapate etc.

Most of the time, when people talk about ULLs, they are talking about cutoff lows, just an FYI.

Regarding how the shortwave will move, it's combination of vorticity advection and differential temperature advection, which are the two terms in the quasi-geostrophic height tendency equation. Do you understand the two bolded terms before we go further?

[Cyclonicjunkie]

Most of the time, when people talk about ULLs, they are talking about cutoff lows, just an FYI.

Regarding how the shortwave will move, it's combination of vorticity advection and differential temperature advection, which are the two terms in the quasi-geostrophic height tendency equation. Do you understand the two bolded terms before we go further?

I understand Vort adv but not dif temp adv. Sidebar: Would it be safe to say that generally there is an ull where the max Vort is inside of a sw trough?

[am19psu]

I understand Vort adv but not dif temp adv.

I'm going to assume you understand normal temperature advection. Let's use 500mb as an example. If you have warm air advection above 500 mb (on average), the thickness will increase, causing 500mb heights to decrease. Likewise, if you have cold air advection below 500mb, the thickness will decrease and also cause 500mb heights to drop. Does that make sense?

Sidebar: Would it be safe to say that generally there is an ull where the max Vort is inside of a sw trough?

I don't know any meteorologists that use the term ULL for anything but a cutoff low. IOW, an upper low that has an entirely closed off height contour.

[Cyclonicjunkie]

I'm going to assume you understand normal temperature advection. Let's use 500mb as an example. If you have warm air advection above 500 mb (on average), the thickness will increase, causing 500mb heights to decrease. Likewise, if you have cold air advection below 500mb, the thickness will decrease and also cause 500mb heights to drop. Does that make sense?

Yes

I don't know any meteorologists that use the term ULL for anything but a cutoff low. IOW, an upper low that has an entirely closed off height contour.

So what i'm talking about would just be a shortwave until it closes off?

[am19psu]

So what i'm talking about would just be a shortwave until it closes off?

You got it.

Now, from there, you would forecast the shortwave is going to move via vorticity advection at 500 mb and/or by differential thermal advection (either WAA above, CAA below, or both). This is QG theory which ignores vorticity generation by latent heat release, but that only matters in hurricanes and summertime MCSs.

[Cyclonicjunkie]

You got it.

Now, from there, you would forecast the shortwave is going to move via vorticity advection at 500 mb and/or by differential thermal advection (either WAA above, CAA below, or both). This is QG theory which ignores vorticity generation by latent heat release, but that only matters in hurricanes and summertime MCSs.

Ah thanks so much, you have been very helpful.

Iv'e learned everything I know from the surface up. I guess thats backwards, and I should have started in upper air meteorology, since the surface responds to the upper levels