Fujita Phil wrote:Typical... I leave Qtown about 11am and thought that if it rained down through these tempertures I might see snow. I get to Dunedin about two and my collegue rings me going through the Gorge saying it's snowing
I have had a 31mb drop over 19hrs so far today.
We're going down downdowndowndowndowndowndowndowndowndown
Heh! Clever stuff. Wish I had your patience Phil!
Omarama dropped from 1020 to 988 in around 21 hours.
I was to see a band playing in Chch tonight, but they were coming up from Queenstown today and delayed by the snow (the Lindis closed) so that when they got here, it was too late to start, as the venue (the Dux) isn't licenced to stay open beyond midnight. At least I got my money back.
Well the earlier predictions (both by MetService and on this forum) of a possible snowfall in the South Island in the latter part of this week have come true. Ironically the falls have come not from the cold southerly of late Wednesday (which turned out pretty weak), but from the 'mild' northeasterly of yesterday, which just happened to bring the moist air to the inland South Island before frosts could thaw. MetService failed to realise this until it happened.
tich wrote:Well the earlier predictions (both by MetService and on this forum) of a possible snowfall in the South Island in the latter part of this week have come true. Ironically the falls have come not from the cold southerly of late Wednesday (which turned out pretty weak), but from the 'mild' northeasterly of yesterday, which just happened to bring the moist air to the inland South Island before frosts could thaw. MetService failed to realise this until it happened.
Our snow warning clients had a warning of this event on Monday, predicting light falls above 500m in Otago and 700m in Canty on Thursday night, with heavier falls above 1000m. As Steven says, it was fairly easy to see it was going to happen as an event, its just getting the exact levels and exact locations which is a bit tricky in this warm advection situation.
And Ben, its nothing to do with frosts. Frosts only happen in the lowest 20-50m of the atmosphere, and snow doesnt have a chance to melt in the length of time it takes to fall through that distance. Its to do with the cold southerly air which remained over the SI in the weak high after Wednesday's S-SW outbreak. The cold air remains trapped near the surface where the wind speed is light, which is why it often snows to lower levels in the basins (where the air is contained) than on the hills/plains.
[quote="spwill" A frosty ground surface will help wet snow to settle.[/quote]
Thats true.
Out of interest I checked back, and this was our forecast for Otago from the Fencepost site on Monday and Tuesday:
"Cloudy on Friday with scattered rain developing late in the day and cool northeasterlies becoming strong and gusty. A period of heavier rain at night. Snow above 500m, possibly heavy for a time above 800m later on Friday night."
Out of interest I checked back, and this was our forecast for Otago from the Fencepost site on Monday and Tuesday:
"Cloudy on Friday with scattered rain developing late in the day and cool northeasterlies becoming strong and gusty. A period of heavier rain at night. Snow above 500m, possibly heavy for a time above 800m later on Friday night."
Just for the record, the snow started falling here just after 11 AM. It was heaviest at approximately 3 PM. It finally stopped around 5 PM and was followed a while later by rain/sleet. That lasted into the night (not sure whether continued or stopped later...I was sleeping...
I measured a maximum depth of something like 4-5" (measured on an open flat surface). There's still a lot of snow lying around now but it's a lovely sunny day and not too cold, so it might not last a lot longer!
Yesterdays midday freezing levels at both Invercargill and Paraparam were around the 2000m level, quite high for June. Yet the snow fall was down to 300m.
Warm advective snowfall tends to suprise at the level it can fall to.
The cold southerly change on Wednesday, set the stage for this snow fall as Tony says. The sheltered inland valleys tend to lock in a low freezing level. And, Yes, I think radiative cooling contributes. Severe overnight frosts help to chill out the environment.
In sunny Nelson . Overcaste here with patchy light rain about . Looks like heavy rain out over the Western Mnts. Could see CB out that way this Morning.
. Looks like heavy rain out over the Western Mnts. Could see CB out that way this Morning.