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Warmer air pushing into colder air mass. Here in New Zealand subtropical lows can create heavy snow in Winter as the warm front pushes south into low level cold air. The eastern South Island above 200m is where this mostly occurs. The snow can fall to sea level. Most of our heavy snow events occur from this type of set up and the Canterbury region is the sweet spot for this.
Thanks, I understand now. That's a similar setup to one of the ways we can get snow here; I was surprised that places in New Zealand would be cold enough at sea level under such scenarios for snow to be produced. What kind of sea-level air temperatures are we talking about?
PS. These would not be subtropical lows in this situation as subtropical lows, by definition, do not have fronts and are not associated with significant warm (or cold) air advection.
Curious what's meant by this. Or did you mean to say cold advection?
Warmer air pushing into colder air mass. Here in New Zealand subtropical lows can create heavy snow in Winter as the warm front pushes south into low level cold air. The eastern South Island above 200m is where this mostly occurs. The snow can fall to sea level. Most of our heavy snow events occur from this type of set up and the Canterbury region is the sweet spot for this.
In the New York area we call them Southwest Flow Events or SWFE's. If a storm moves to the south of NYC and doesn't transfer energy to a secondary off the coast, we often get a heavy "thump" of snow from the invading overrunning warm air mass. Sometimes the storm will end with a change to drizzle but because there was so much snow in the initial approach it is remembered as a 6"-8" snowstorm even though technically it wasn't an "all snow" event. We had one of those in New York, if I recall correctly, in December 2008, a week before Christmas. The more "classic" storms occur when the energy transfers from the inland storm to one off the coast. The wind switches to northeast, often but not always helping to lock in the cold air. Those storms are quite memorable. Examples include the "Mayor Lindsay" storm of February 1969.
I think NZ is too warm for freezing rain. The colder parts of NZ can see light rain showers moving in on frosty morning and creating some ice but this is not freezing rain.
That's exactly what freezing rain is - not common in NZ, but I've seen proper freezing in rain in Otago and Southland a number of times.
The reason it isn't known as freezing rain around here (imo), is because most people assume it's rain that has fallen and then frozen during the night, which is relatively common around here - to be aware of freezing rain here, one needs to be aware of the sequence, and as the precipitation part is so brief and confined to night/early dawn, it's easily missed.
Thanks, I understand now. That's a similar setup to one of the ways we can get snow here; I was surprised that places in New Zealand would be cold enough at sea level under such scenarios for snow to be produced. What kind of sea-level air temperatures are we talking about?
PS. These would not be subtropical lows in this situation as subtropical lows, by definition, do not have fronts and are not associated with significant warm (or cold) air advection.
Lows with sub tropical origin or central Tasman sea lows with a moisture feed from the sub tropics. The sea level snow is not common. The inland valleys and plateaus see most of the low level snow
That's exactly what freezing rain is - not common in NZ, but I've seen proper freezing in rain in Otago and Southland a number of times.
The reason it isn't known as freezing rain around here (imo), is because most people assume it's rain that has fallen and then frozen during the night, which is relatively common around here - to be aware of freezing rain here, one needs to be aware of the sequence, and as the precipitation part is so brief and confined to night/early dawn, it's easily missed.
Freezing rain occurs when supercooled water droplets literally freeze on hitting a surface. What typically happens is a layer of cold air dams and is overridden to a low level, leaving a shallow layer of cold air at the surface. It may literally be 40°F at 5000 ft. and 27° or colder below. That means that liquid precipitation is falling through cold air.
This can create a "skating rink" effect. It is rare in the Southern Hemisphere because presumably when it does get wintry cold air is more abundant in the higher altitudes and the lower altitudes become marginally cold enough to support snow.
Freezing rain occurs when supercooled water droplets literally freeze on hitting a surface. What typically happens is a layer of cold air dams and is overridden to a low level, leaving a shallow layer of cold air at the surface. It may literally be 40°F at 5000 ft. and 27° or colder below. That means that liquid precipitation is falling through cold air.
This can create a "skating rink" effect. It is rare in the Southern Hemisphere because presumably when it does get wintry cold air is more abundant in the higher altitudes and the lower altitudes become marginally cold enough to support snow.
Yep, that's pretty much the conditions in which it would happen here - different in process though with the mountains acting as a dam to the moisture (strong westerly rain shadow) and the cold air being the result of 10-12 hours of radiation frost. Brief incursions of rain over the ranges and the cold air are all that it takes.
A different process to what I witnessed in the lower South Island, where I've seen freezing rain on lowland plains.
Lows with sub tropical origin or central Tasman sea lows with a moisture feed from the sub tropics. The sea level snow is not common. The inland valleys and plateaus see most of the low level snow
Those are midlatitude lows, or more properly midlatitude cyclones, not subtropical lows.
Those are midlatitude lows, or more properly midlatitude cyclones, not subtropical lows.
Mid latitude lows are common, and are easy to distinguish from systems that originate from around the Coral Sea, and which also have lower pressure centres.
Freezing rain occurs when supercooled water droplets literally freeze on hitting a surface. What typically happens is a layer of cold air dams and is overridden to a low level, leaving a shallow layer of cold air at the surface. It may literally be 40°F at 5000 ft. and 27° or colder below. That means that liquid precipitation is falling through cold air.
This can create a "skating rink" effect. It is rare in the Southern Hemisphere because presumably when it does get wintry cold air is more abundant in the higher altitudes and the lower altitudes become marginally cold enough to support snow.
The Ice storms in USA look spectacular. From my observation in New Zealand I have only seen cases where light rain creates some ice by landing on frozen ground surface rather than super cooled rain droplets coating everything in ice.
Mid latitude lows are common, and are easy to distinguish from systems that originate from around the Coral Sea, and which also have lower pressure centres.
We've had this conversation before. Any system that has any kind of front attached to it is a midlatitude cyclone by definition. Subtropical lows do not have fronts attached to them, also by definition.
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