Snow Watch 2016

Coeta wrote: Try skydiving through a hailcloud, - perfect weather in the plane at 11k AGL, then you fall at +-220 kmh and look like a paintball convention used you as target at point blank range once you reach the ground.

That sounds painful!

I have been in the open in Berg hail storms at least 10 times, mostly on my summer GTs. Fortunately the hail stones never seem to be too big up there.

Is it just me, or are massive hail storms becoming much more common these days? Perhaps I have only started noticing them now.

Not sure if they are worse these days, but up here in Gauteng they are definitely more frequent.

ghaznavid wrote:
Is it just me, or are massive hail storms becoming much more common these days? Perhaps I have only started noticing them now.

Ghaz - during El Nino years the hail storms are more intense. There is good data from Cedara which shows this. I think I know the reasons. To make an intense thunderstorm you need a few things, including:
a) warm, moist air near the surface in a layer 1-2 km or more deep
b) a way of stopping the convection from leaking the energy out of the surface layer too quickly - i.e. the energy (CpT + Lq where T is temp and q is specific humidity and Cp and L are constants) needs to be trapped near the surface until large amount of it have accumulated.

In El Nino years T is higher (more sunshine, less cloud) and q is higher because sea surface temperatures in the Indian Ocean are higher. So there is a greater stash of energy (CpT+Lq) in the lowest 2 km.
In El Nino years the air is also sinking on a large scale which is the mechanism by which the energy gets contained near the surface. Sinking air prevents the convection from releasing too early. Sinking air also creates clear skies and drought and acts like a lid on a container that is being heated from below. When the lid does finally blow off then a vicious storm ensues.

@tiska: are there any longer term methods that are able to predict heavier snowfalls in the berg than in other years?

Captain wrote: @tiska: are there any longer term methods that are able to predict heavier snowfalls in the berg than in other years?

Not that I know of (and its my day job). The systems that bring snow in winter are of midlatitude origin and those weather systems have little or no long term predictability. For the summer, in some years in southern Africa, there is some predictable skill a few months ahead when it comes to droughts and very wet years - mainly as a result of ENSO (La Nina and El Nino). ENSO tends to get stuck in one pattern for many months at a time which is how we get predictability.

That said, it is possible to explain why one winter produced more snow than another, but only retrospectively, once the season is over.

Currently less than 3 deg C on the escarpment at 3:15 pm (6 April) - the coldest its been since last winter - with flow coming from south of Marion Island (which is half-way to Antarctica). Its about 2 degrees in Marion Island as well but that flow warms up when crossing the Agulhas system and then cools down again when lifted over the escarpment.
Chances are it will snow later this evening as some deep convection is moving southwards at higher altitude over the escarpment.

Data above from the GFS forecast system. The lines show low level winds and the colour relative humidity at low levels.


Image above from Meteosat SEVIRI thermal imagery for 2pm SA time on 6 April.
Red stuff is deep convective cloud.

tiska wrote: Data above from the GFS forecast system. The lines show low level winds and the colour relative humidity at low levels.

That is a pretty looking weather map

Macc wrote:

tiska wrote: Data above from the GFS forecast system. The lines show low level winds and the colour relative humidity at low levels.

That is a pretty looking weather map

The actual website is even nicer - because somehow, some techie guy has managed to make one time step animate:
earth.nullschool.net/#2016/04/07/1500Z/wind/isobaric/850hPa/overlay=relative_humidity/orthographic=-344.86,-27.58,981/loc=0.338,-17.552

If you click on where is says EARTH, all the options open up. It includes forecast data and goes back in 3 hourly time steps a few years too.

Instructions verge on laconic though.