The National Weather Service Forecasts-

TODAY...SUNNY. HIGHS 19 TO 25. NORTHEAST WIND 10 TO 15 MPH.

TONIGHT...MOSTLY CLEAR. LOCALLY WINDY. LOWS 10 TO 20...EXCEPT
AROUND ZERO IN WIND SHELTERED AREAS IN THE MENDENHALL VALLEY.
NORTHEAST WIND 10 TO 15 MPH. NEAR DOWNTOWN JUNEAU AND
DOUGLAS. NORTHEAST WIND 10 TO 20 MPH INCREASING TO 20 TO 30 MPH WITH GUSTS TO AROUND 55 MPH LATE.

SUNDAY...SUNNY. LOCALLY WINDY. HIGHS AROUND 23. NORTHEAST WIND 10 MPH. NEAR DOWNTOWN JUNEAU AND DOUGLAS...NORTHEAST WIND 20 TO 30 MPH WITH GUSTS TO AROUND 45 MPH.

SUNDAY NIGHT...MOSTLY CLEAR. LOCALLY WINDY. LOWS 10 TO 18.
NORTHEAST WIND 15 TO 25 MPH. NEAR DOWNTOWN JUNEAU AND
DOUGLAS. NORTHEAST WIND 20 TO 30 MPH WITH GUSTS TO AROUND 40
MPH...DIMINISHING LATE.

With the warm weather from 2 weeks ago, the rain and heavy dense snow, the lower snowpack has settled and bonded quite a bit.

There are still multiple weak layers lower in the snowpack but the heavy dense snow above them appears to be supportive at this time. Be cautious as new loads are placed on these already weak layers by new snow or even by additional wind loading.

We had several inches of new snow deposited Saturday and Monday. This has placed some additional weakness in the snowpack in places with wind deposits.

Look to see continued areas of wind loading as the snow in place is affected by winds of 10+ MPH throughout most of the next few days.

Thursday natural avalanche releases were sighted on multiple aspects due to wind loading. Be aware there are pockets of instability.

With very little snow on Mt Juneau in the urban starting zones avalanche danger is LOW at this time. Yet some of the gullies are starting to see fair snow accumulation due to crossloading from the winds.

Please remember this is not a backcountry forecast.

Please be aware that fieldwork continues to show multiple weak layers in the snowpack and natural avalanches have been sighted recently.

Backcountry danger levels could be considerably higher.

Once you?ve gathered pre-forecast information, you?re ready to evaluate the current weather situation, looking at conditions during the preceding 24 hours. Specifically, you?ll examine weather variables that have the greatest impact on snowpack and avalanche potential (precipitation, wind, temperature, and cloud cover) and determine if they?ve exceeded critical thresholds. Solar radiation is also important but will be considered in combination with cloud cover.

Since most avalanches are associated with recent or newly fallen precipitation, you should collect the following information for any recent and/or ongoing precipitation events:

?Amount of new snowfall
?Rate of accumulation
?Snow water equivalent
?New snow density

New snow amount: New snowfall is usually recorded to the nearest inch (cm) at 24-hour intervals or sometimes more often during storms. Measurements are taken manually from a storm board (snow board) at the site or automatically, using a remote sensing device, such as an acoustic snow height sensing instrument.

Snow accumulation rate: We measure the water content or SWE of new snow to help us determine its density and learn about the weight of new snow being added to the pack. Record SWE to the nearest one-hundredth of an inch (or tenth of a millimeter). Measure it using a melting precipitation gauge or by bringing a snow sample from a standard precipitation gauge indoors, melting it, and measuring the height of the water. It can also be measured by weighing a core sample of new snow using a calibrated scale designed for weighing snow collected with a snow tube. For more information, see COMET?s Snowmelt Processes module at http://www.meted.ucar.edu/hydro/basic/Snowmelt/.

New snow density: Snow density is another way of expressing how much weight is being added to the snowpack. For a given snow depth, high-density snow adds more weight (water) than low-density snow. Snow density is usually expressed as a dimensionless ratio of snow water content to snow depth (such as 1:10) or as a percentage of snow water content to snow depth (such as 10%).

To calculate density, divide the amount of water contained in the snow by the depth of the new snow. The higher the value, the more water is in the snow.

Here are a few exercises.

What?s the density of 20 inches (50 cm) of snow that contains 2 inches (5 cm) of water? (Choose the best answer.)

a) 1:10 or 10% .
b) 2:10 or 5% .
c) 20:2 or 1000% .
d) 20:1 or 2000% .

The correct answer is A.

If you divide the snow water content (2 in or 5 cm) by the snow depth (20 in or 50 cm), you get 1:10 or 10%.

Which snowpack weighs more? (Choose the best answer.)

a) 20 inches (50 cm) of snow with 2 inches (5 cm) of water .
b) 20 inches (50 cm) of snow with 1 inch (2.5 cm) of water .

The correct answer is A.

The first pack has a density of 10% (2 inches / 20 = 1:10 or 10%), whereas the second has a density of 5% (1 / 20 = 1:20 or 5%). The snow depths are the same but the denser snow contains twice as much weight as the less dense snow.

For more exercises like these, see the COMET module Snowpack and Its Assessment at http://www.meted.ucar.edu/afwa/snowpack/.

Storm trend: During the course of a storm, temperature fluctuations will produce snowfalls with varying new snow densities.

?Storms that begin with warmer temperatures and higher-density snowfall and end with colder temperatures and lower-density snowfall produce a more stable layer. These are known as right-side-up storms because lighter snow overlays heavier snow.
?Storms that begin with colder temperatures and lower-density snow followed by warmer temperatures and higher-density snow produce a more unstable layer. These are referred to as upside-down storms since heavier snow overlays lighter snow.
When tracking incoming storms, be sure to consider the nature of the underlying or old snow surface. If new snow falls on surface hoar or near-surface facets, an unstable situation may develop regardless of the new snow?s density.

Rainfall: Rainfall adds weight to a pack. Especially in maritime climates, you should closely monitor the snow/rain level during storms since rain on snow almost always causes avalanches.