Avalanche hazard level 1

(Continuous snow coverage, few snow to the ground, depth hoar layers)

Dolomites - January 2006 the 16th

ARPAV – Centro Valanghe Arabba

Condition for the avalanche hazard level: low

Degree of Degree of dangerdanger SnowpackSnowpack Avalanche probability Avalanche probability

lowlow

The snowpack is generally well bonded and stable or to weak cohesion and without tensions.

Triggering is generally possible only with high additional loads [2] and few very steep extreme slopes. Only a few small natural avalanches (sluffs) possible.

Indications for excursionists mountain,

climber, backcountry skiers and ski out of the

bound

Indications for roads, ski area and countries

Generally favourable conditions.

Any indication.

Study Area (1800 km2)

Snow data

Typical snow profile of on January 2006 the 16th

A lot of layer of:Faceted crystalDepth Hoar

Snowpack microstructure: grain type

Typical Rutschblock R=716.01.2006

Altitude: 2100 m a.sl.Exp.: Est

Snowpack Natural stability index Sn 38

• Natural stability index =2,1 – 2,3

• Skier stability index =1,4 – 1,7

Snow cover distribution 16.01.2006

• A Snow depth:– 1500 m (a.s.l): 20 – 60 cm– 2000 m (a.s.l.): 50 – 90 cm

• B Snow distributions:– On the southern slopes the snow

cover is discontinuous to 1700 m– On the slopes in shadow the snow

is present at low altitude.

• C Snow surface:– The superficial layer of the snow

cover presents weak cohesion at every altitudes and in all the exposures with some wind crusts.

A

BC

Avalanche activity

• D Natural avalanches– Any observed avalanche.

• E Skiers avalanche– Any observed avalanche (Ski out of

bound even on extreme steep slopes)

• F Wind activity: – Weak wind activity (all exposures)

D

EF

Avalanche activity

SluffSluffLength < 50 m

Volume < 100 m3

Small avalancheSmall avalancheLength <100 m

Volume < 1.000 m3

Medium avalancheMedium avalanche

Length <1.000 m

Volume < 10.000 m3

Large avalancheLarge avalanche Length <1.000 m

Volume < 10.000 m3

natural No avalanche (few some many numerous)

No avalanche (few some many numerous)

No avalanche (few some many numerous)

No avalanche (few some many numerous)

low additional load

No avalanche (few some many numerous)

No avalanche (few some many numerous)

No avalanche (few some many numerous)

No avalanche (few some many numerous)

large additional load

No avalanche (few some many numerous)

No avalanche (few some many numerous)

No avalanche (few some many numerous)

No avalanche (few some many numerous)

zone of the avalanches observation

Meteorological data

Wind speed and direction

Air Temperature

Average (1984-2005)

New Snow New Snow New Snow

24 h (HN)24 h (HN)

HW HW

24 h24 h3 days new 3 days new Snow sumSnow sum

Manual weather stations

Belluno, 290 m 0 cm === 0 cm

Falcade, 1200 m 0 cm === 0 cm

Cortina,1200 m 0 cm === 0 cm

Arabba, 1600 m 0 cm === 0 cm

Automatic weather stations

C.Pradazzo,2200 m 0 cm === 0 cm

M.A.Ornella, 2200 m 0 cm === 0 cm

Summary of the informations and of the data and their importance for the avalanche forecast for the

day January the 16th

Avalanche forecast: Anselmo Cagnati, Mauro Valt and Renato Zasso

Analysis checklistAnalysis checklist

Factor Data Stability?

Y/N/?

Importance

I. Avalanche Activity and Stability TestsI. Avalanche Activity and Stability Tests

Avalanche Activity None in last 2 days YY Medium

Stability Test R7 YY High

II. Snowpack ObservationsII. Snowpack Observations

Profile Weak resistance ( little thickness) Y?Y? High/Low

Settlement Few NN Low

Temperature Long period of low temperatures N - YN - Y Low

Temperature Gradient High 33 °C/m N - YN - Y Low

Snowpack Height 50 – 90 cm YY High

III. Meteorological ObservationsIII. Meteorological Observations

Precipitation None in last 3 days YY Low

Wind Speed Weaks NN High

Wind Direction NW NN Low

Air Temperature Low Air Temperature –12/ -17°C NN Low

Weather forecast Weaks wind in the 24 h, strengthening in the next 72 h YY High

Auxiliary matrix for the avalanche report

Avalanche bulletin

Situations:Avalanche hazard: low (level 1)

Since the beginning of the last week the weather kept on being good with mainly clear sky ad very good visibility. Since yesterday temperatures felt down especially aloft and the thermal inversion has almost disappeared. Winds were generally light, also if local strengthening were registered only on the most high altitude on the Dolomites. With low temperatures, snow had a significant cooling at every altitude with consequent increasing of kinetic growth crystals and surface hoar which in some cases is well grown. Only on the extreme steep slopes exposed to S and W the surface layer presents local sun-refrozen crusts which are however not very much strengthening. The avalanche danger is generally low and eventual artificial releases, generally only with large additional load, are possible only on isolated extremely steep slopes characterized by snow drift deposits. Since the central hours of the day, with the sun, on the grassy steep slopes or at the base of the rocks single little natural avalanches of moist snow might occur.

Wind slab on faceted crystals,

soft snow or crusts.Extremely steep

slopes.

Photographic documentation

None sluff or small avalanche on the S-W slopes (Tre Cime di Lavaredo)

None sluff or small avalanche on the S slopes (Sappada)

None sluff or small avalanche on the S-E slopes (M.te Piz Boè, Campolongo)

None avalanche in skiing out of the bound (N-E slopes) (M.te Civetta)

None avalanche in skiing out of the bound (S-E slopes) (M.te Civetta, Falcade)

Backcountry ski on extremely steep slope (Monte Pelmo)

Thanks