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+--- Thread: Virga and Mauna Kea (/showthread.php?tid=17193)
Virga and Mauna Kea - TomK - 05-08-2016
It's currently snowing on Mauna Kea even though humidity there is less than 50% and temperatures being a touch above freezing level. I doubt enough snow will fall to survive until dawn, but early risers might want to check the webcams:
http://mkwc.ifa.hawaii.edu/current/cams/
Basically, virga is precipitation from mid to high-level clouds that evaporates before it gets to ground-level. However, since the summit area of MK is so high, it can receive this type of precipitation.
It's nasty one for the observatories as the usual conditions that suggest snowfall are rarely met yet the snowfall can be significant.
RE: Virga and Mauna Kea - Kenney - 05-09-2016
Wow Tom, thanks for the visuals! Your perspective of the island is so unique and awe inspiring!
RE: Virga and Mauna Kea - TomK - 05-09-2016
Thanks, Kenney! You definitely get to see some atmospheric phenomena at the summit you don't get to see elsewhere.
RE: Virga and Mauna Kea - PaulW - 05-09-2016
Always a good day when I learn a new word! Thanks Tom.
RE: Virga and Mauna Kea - TomK - 05-10-2016
No problem, Paul and thank you too. I've always felt it's important to learn one new thing every day. It keeps the brain cells ticking over and the neurons firing.
RE: Virga and Mauna Kea - AKpilot - 05-10-2016
Virga, all Quadrants is a common call here in Alaska!! Saw plenty today into Bethel.
AKpilot
We're all here, because we're not all there!
RE: Virga and Mauna Kea - TomK - 05-10-2016
AKpilot - I'm curious. Is the call made because it looks cool or it might cause icing problems? Or something else.
RE: Virga and Mauna Kea - AKpilot - 05-10-2016
Virga ca be tricky. Can be the harmless die off a cumulus that never quite got convective enough......could also be something convective without a tight enough temp/dewpoint for it to reach the ground.
I have seen virga spawn wicked windshear and even saw it push cars in a Centennial Airport parking lot.
They call be full of a little to a lot or rime and even clear ice.........more tomorrow. off to bed for the ALaskan
ZzZZZZZZZZZ
We're all here, because we're not all there!
RE: Virga and Mauna Kea - TomK - 05-10-2016
Thanks for that, AK, it certainly answered my question!
The virga above MK the other day was likely caused by convection, similar to what you describe, but on odd occasions it can come from mid-level clouds when there is no convection. It's rare but has caught us flat-footed once or twice. Humidity is low, the sky has loads of cloud but we're open waiting for gaps. Suddenly there's a call from someone at the summit that it's snowing.
We're not so interested in icing (I know that's a big deal for you) but getting moisture on extremely sensitive electronics, or on the mirror itself. Frosted primary mirrors don't work well.
Given most of the observatories are switching to remote operations, summit conditions described by a human are less common, so there are some automatic systems up there to detect rain, snow and ice, but this project is still in its infancy.