Snow conditions 23.3.2018

General hazard level - Friday, 23.3.2018

Hazard is 3rd degree on the European five-level scale - CONSIDERABLE.

Main problem: weak layers, wind slab

Hazard pattern: Cold weather, unbonded fresh snow with wind



Risk assessment

Avalanche danger above about 1500 m altitude is mostly CONSIDERABLE, 3rd degree. Lower down, due to smaller snow amounts, danger is MODERATE, 2nd degree. The main issue remains the weak bonding between the old hard layer and larger quantities of newer unbonded snow. New layers, especially in wind slabs, are also very fragile due to the frost. Steep slopes and areas with wind-deposited snow are particularly dangerous. There, even with minor snowpack loading, you can trigger an avalanche. Probability of spontaneous avalanching increases slightly during the day, especially on sun-exposed slopes.



Snow conditions

Mostly dry and cold mountain weather continues, mid-week stronger sun also affected sun-exposed slopes. Snow fallen until Monday morning mostly remained dry and light and has not bonded with the old hard base, strengthening wind in recent days also additionally drifted it into wind slabs and cornices in many places. Locally on sun-exposed slopes, crust formed that does not bear human weight. Old snowpack remained partially refrozen, hard and still slightly moist. On wind-exposed sites where snow is scoured, old snow froze and is hard and icy. Conditions are locally very variable, especially on sun-exposed areas where alternating wind and sun effects are evident even over short distances. Upper layer in deposited snow slabs can transform under sun influence during the day, contributing to increased instability and possibility of small and medium spontaneous avalanches - especially at transitions between convex and concave features near ridges. Locally on sun-exposed slopes, cracks are visible, which during daytime travel could be release areas for slab avalanches.



Forecast weather development

In coming days variably cloudy, some summits occasionally in fog. Northeasterly wind will gradually weaken. Temperature at 1500 m around -3, at 2500 m initially around -10 °C, then slightly less cold in lower elevations. Daily temperature cycle will become more pronounced. Freezing level at night between 800 and 1000 m, during day above 1300 m. Sun-exposed slopes somewhat warmer. From early week, situation will warm and melt more, zero isotherm will shift well above 1500 m during day.



Tendency of snow conditions

Conditions will remain at least locally relatively unfavourable. Wind weak, but temperatures in mountains slowly rising. Main snowpack transformation sources due to daily cycle and sun - quite differently on sun-exposed/shaded slopes. Due to low temperatures, surface snow layer will remain dry and soft mainly in shaded areas, on sun-exposed slopes it will melt considerably during day under sun and refreeze at night, crust forming, less pronounced in high mountains. Snow will transform faster especially in mid-mountains, there avalanche danger slightly higher during day, but overall slowly decreasing, crust strengthening. In shaded areas, possibility remains to trigger wind slab still unprocessed on steeper slopes even with minor loading. On sun-exposed, upper layer in deposited snow slabs will transform under sun during day and can contribute to increased instability and possibility of small/medium spontaneous avalanches. Triggers can also be snow shedding from rocks or scree.



Next issue: Monday, 26. 3. 2018



Source: ARSO