Elsewhere in Weather News: February 8th, 2014

Massive Ice Storm Paralyzes Slovenia

A massive ice storm crippled a large part of the Central European country of Slovenia earlier this week. Freezing rain accumulations of 100mm wrecked havoc, encasing all unheated surfaces in a thick layer of ice. The ice brought down power lines, fell trees, and froze vehicles in place, leaving at least 50,000 houses without power at one point. Slovenian authorities estimate that the storm caused at least $89 million in damages and destroyed 40% of Slovenia’s alpine forests. The pictures coming out of Slovenia from this event are extraordinary:

  

  • A car encased in ice
    A car encased in ice.
  • A man chips the ice off his car in Postojna, Slovenia
    A man chips the ice off his car in Postojna, Slovenia.
  • Forests were severely damaged by the ice storm.
    Forests were severely damaged by the ice storm.
  • Road signs coated in a thick layer of ice.
    Road signs coated in a thick layer of ice.

Freezing rain is a common weather phenomena, but for it to occur on this scale is rare. In most situations, freezing rain occurs ahead of a warm front as warm, above-freezing air overrides a shallow layer of below-freezing air near the surface. As snowflakes fall through that warm above-freezing layer they melt into rain drops. This allows it to rain, since those rain drops don’t have a chance to refreeze before hitting the surface. However, once this rain strikes the surface, it freezes instantly, forming a layer of ice. Usually the warm front that causes the freezing rain will be moving, preventing the freezing rain from sitting over one area for a prolonged period of time. However, in some situations the warm front will stall out, or move parallel to an area, causing freezing rain to persist for an extending period of time. In the case of Slovenia’s ice storm, it appears a slow moving weather pattern allowed the freezing rain to sit over the same area for an extended period of time, generating the large ice accumulations seen above.

Sources:

http://www.businessinsider.com/photos-of-ice-storm-in-slovenia-2014-2

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2014/02/07/craziest-ice-storm-photos-youll-ever-seen-from-slovenia-photos/

Elsewhere in Weather News: December 21st, 2013

Southern Ontario, Midsection of US Anticipate Ice Storm

A major ice storm has been taking shape as of Friday night across parts of Oklahoma and Texas and will continue to push northeast. A potent cold front with Arctic air filtering in behind it is clashing with gulf moisture moving north and thereby creating prime conditions for ice accumulation from Oklahoma all the way to southern Ontario. Dangerous travel conditions are expected as there could be significant ice accumulation due prolonged periods of freezing rain through this weekend. With this comes the possibility of downed power lines so residents have been made aware to prepare for power outages across southern Ontario. So overall, not ideal conditions for holiday travel this weekend as all kinds of precipitation will be falling across the eastern half of the US and southern Ontario.


Freezing rain sounding from Oklahoma on Friday evening. Note the shallow freezing layer near the surface where the arrow is. (Souce: Twisterdata)
Freezing rain sounding from Oklahoma on Friday evening. Note the shallow freezing layer near the surface where the arrow is. (Souce: Twisterdata)

Freezing rain forms when there is a deep layer of warm air that is above freezing aloft. As the ice crystals fall and meet the warm layer, they melt and become raindrops while falling towards the ground. A shallow layer of cold air just above the surface of the earth must also be present for freezing rain to form. Supercooled water droplets – drops of liquid water that exist in below freezing air, will be in place and won’t have enough time to freeze into ice pellets, thus will freeze (as ice) on contact as they hit the ground.

In addition to this, a severe weather outbreak is expected in Dixie Alley of the US today. The outbreak is associated with the same system as the cold front slices through the warm, moist air mass in place. A moderate risk has been issued by the Storm Prediction Center as well as a 15% hatched area for tornadoes in Mississippi and northern Louisiana. Chances of tornadoes are quite high, the only possible limiting factor is that CAPE will be fairly low (only around 500-1000J/kg) but this will still be sufficient for supercells which will quickly evolve into a quasi-linear convective system – a line of severe thunderstorms that can have bowing segments. SPC gives fairly strong wording for today in Dixie Alley saying that “there is potential for several tornadoes – some of which should be strong”.

By Monday night the system will have moved off the US East Coast but will still be a weather-maker for Atlantic Canada.