After a month filled with many foggy mornings, June has continued the trend with another brilliant event for the first day of winter. It was an interesting scenario, and probably the first time I have seen this sort of event, mind you every time I head out, I see something unique.
Judging by the Clare AWS obs fog, or near fog conditions were prevalent the whole night with 99% humidity recorded. It was high enough for long enough that the rainfall from the previous evening still hadn’t dried in places the next morning. The initial high readings came from low orographic cloud, which transitioned to clearer skies forming radiation fog. Maritime Sc moved in from the south, breaking the inversions and causing the fog to advect west, surviving best where breaks in the Sc bank were. This is the point I arrived at, with some misty fog banks cruising by to the south but not much happening. However as the sun began to rise, the Sc started to break up, which caused two things to happen. The mixing started to stir the air up and a breeze gradually began to strengthen from the east. At the same time, the rapidly breaking cloud, allowed radiative cooling to occur in the valleys and this combination caused a remarkable change in the fog patterns, causing a ‘flash fog’ for lack of better wording. The easterly winds were already so close to saturation, any movement up hills caused fog to form. It came in where I was as a gentle mist at first, thickening to 200m visibility after 20 odd minutes. However within minutes of the sun rising, it thickened dramatically with the strengthening wind and drove cascading fog over the range I was on. You could literally watch it form 100m to my east, and then die on the leeward side, 50m to my west. During this time, the valleys went from being clear, to covered in a thin layer of thick mist and so there were now two levels on which the fog was present.
Given the exposed nature of the ridge fogs, and the relative thinness of the valley fogs, it wasn’t long before the fog burnt away, being mostly gone within an hour of sunrise, having risen and formed stratocumulus again.
As the fog thickened over the range, the low sun caused a brocken spectre to occur behind me, the first time I have seen this kind of optic! And surely a hard one to find given SA doesn’t have a great deal of mountainous terrain.
The fog level began to rise as the sun warmed the air, however the fog in the valleys continues to thicken. Interesting effect looking from just within the fog level, down towards the valley fog.
A quick drive into the Hill River Valley and some stock standard radiation fog around, made for damn nice light through the tree tunnels though!
Looking like a dry start to winter unfortunately with highs dominating…so while we will probably get stuff all rain which we really do need (no real stream flows yet in the major rivers…thanks to the very dry Spring/Summer of last year), the fogs and frosts will feature heavily.