Avalanche Bulletin Saturday, 19.04.2014, at 07:30
Moderate danger widespread, beware fresh snowdrift
Avalanche danger in Tirol has increased somewhat due to snowfall and wind, the danger level is moderate far and wide. The major peril stems from fresh snowdrift accumulations which formed yesterday; they tend to be small-sized but brittle due to the low temperatures, making them prone to triggering. In some places, even minimum additional loading is sufficient to release an avalanche (corresponding to danger level 3). Avalanche prone locations are found on wind loaded slopes and ridgeline areas above approximately 1800 m, particularly in west to north to east facing terrain. In steep starting zones, isolated naturally triggered, small, superficial, loose avalanches are a threat.
A cold front brought snowfall as of midday yesterday. Along the Main Alpine Ridge, up to 20 cm of fresh fallen snow was registered; in the other regions, usually 10 cm. High altitude westerly winds were above transport velocity, leading to snowdrift masses accumulating afresh. Due to wintery low temperatures, the drifts are brittle, making them trigger-sensitive.
Alpine Weather Forecast (ZAMG-Weather Service Innsbruck)
Weather in general: the cold front is withdrawing, Tirol is wedged between two small low pressure zones with air masses becoming drier, but instable and thus, prone to showers. Mountain weather today: Snow showers will end, cloud and fogbanks disperse and transform to convective cloud, visibility improve. In the Southern Alps, clouds and showers will persist, but conditions will improve this afternoon. Temperatures are expected to rise noticeably, the zero-degree level soon above 2000 m. Temperature at 2000 m, +1 degree; at 3000 m, -6 degrees. Brisk to strong southeasterly winds to start with, later tapering off to moderate strength.
Short Term Development
Avalanche danger is moderate over widespread areas
[Author: Rudi Mair]
[Translated by Jeffrey McCabe]
Current danger pattern(s)
Experience has shown that even over the course of highly varied winters, nearly identical potential-avalanche scenarios repeatedly arise as recurring danger patterns and are responsible for the greater part of avalanche accidents. An analysis of these patterns was published in the practical handbook "Avalanche - Recognizing the 10 Decisive Danger Patterns" by Rudi Mair and Patrick Nairz in November 2010.
Danger pattern (dp) 6 - cold, loose, new fallen snow and wind
"Wind is the architect of avalanches" this classic adage of Wilhelm Paulcke from the 1930s still has unaltered validity today. Wind influences both falling snow and already deposited snow, it is one of the major formative factors in potential avalanches. If the snow is loosely packed and dry, wind always leads to its transport, thus increasing the danger of avalanches. The colder the transported snow is, the more sensitively it reacts to additional loading, since it becomes even more brittle. This danger pattern is distinct from GM.5 in that the cold, loosely packed snow has not formed over a prolonged cold period, but in a very short time. That means, it either snowed just previous, in low temperatures without wind, and subsequently the wind begins to blow; or it begins to snow without wind, and the wind increases in velocity during the snowfall. This pattern is easy to recognize as a rule.