Risk of a Thunderstorm

Hey all, 

Hope everyone made it through the week okay -- just a quick update on the weather today.

You don't need to be a meteorologist to interpret this radar simulation. The popcorn-type reflectivity suggests convective showers especially later this afternoon for #YVR.

You don't need to be a meteorologist to interpret this radar simulation. The popcorn-type reflectivity suggests convective showers especially later this afternoon for #YVR.

CAPE:

Surface based CAPE over YVR up to 500 J/KG, fairly significant for coastal sections of BC

Surface based CAPE over YVR up to 500 J/KG, fairly significant for coastal sections of BC

I've mentioned this before, but think of CAPE as the amount of buoyant energy available for a parcel of air at the surface as it's accelerated upward by a trigger (for example surface heating). Once the parcel reaches the level of free convection and it becomes warmer than its surrounding, the parcel will continue to rise...

The parcel will continue to rise until it reaches the 'Equilibrium Level' and the parcel once again becomes cooler than it's environment. 

Typical CAPE: 

0- Stable

0-1000: Marginally unstable

1000-2500: Moderately unstable

2500-3500: VERY unstable

One of the greatest strengths for using CAPE is the measurement is integrated through the whole temperature profile -- some other indices just use data from a couple key mandatory fields (LI index). But CAPE isn't one magic number that tells you if they're be thundershowers or not, just the potential for them. There's several big drawbacks of using CAPE includes the limits of parcel theory; it doesn't take into account mixing and freezing of water vapour.

What kind of velocities could we possibly see in some updrafts today?

You're in luck. There's a really simple calculation for that. 

Updraft velocity: Wmax (m/s) = square root (2 x CAPE)

= 30 m/s (theoretical maximum)

So, quite weak for any other part of North America, and Kansas would probably laugh at us...