From the National Weather Service:

TODAY...RAIN SHOWERS. SNOW LEVEL 1500 FEET IN THE MORNING. HIGHS AROUND 44. SOUTHEAST WIND 10 MPH.

TONIGHT...RAIN. LOWS AROUND 35. EAST WIND 5 TO 15 MPH.

MONDAY...RAIN. HIGHS AROUND 44. SOUTHEAST WIND 5 TO 15 MPH.

Over the last 24 hours, the Mt. Roberts weather plot saw just shy of 0.5? of precipitation falling as nearly 7? of snow. Temperatures rose steadily through the day, peaking at 36f around 3pm, and remained just above freezing overnight. Southeast winds rose from the low teens to 20mph. Freezing levels are currently ~1000-1500ft around Juneau.

Today moderate diurnal warming is forecast to be accompanied by light rain and snow and moderate winds.

It is possible that late tonight we will start to see the start of the big rain that is now supposed to whack us with up to 2? of precipitation over the Monday forecasting period. The rapid addition of this weight may step smaller wet slides down to the spatially variable persistent weak layer. Smaller wet slides are expected along with the possibility of release in any weakness left over from yesterdays storm snow.

Todays urban hazard level is MODERATE with a rising hazard trend. Any avalanche activity is expected to remain small is size today. Expect tomorrows forecast to be higher, with significant rain and continuing warm temperatures coming.

Rain-on-Snow Events:

Snow takes time to adjust to changes. When large amounts of liquid water fall on an unsuspecting snowpack, a few hours or days will see preferential percolation channels form on the surface, known as rain runnels. This is demonstration of good horizontal drainage. Vertical drainage channels will also form, drawing water down into the snow.

Depending on the intensity, temperature, and duration of the rain, vertical drainage channels may be able to penetrate multiple crust layers on the way down. If a crust in the snowpack is too thick, it can act as a barrier, forcing the water to flow horizontally again, and potentially undermining stability. It is difficult to predict how rain will interact with many crusts, while others are very predictable. Porousness, density, continuity, and origin are major factors.

Wet avalanches are likely to occur when rain intensity is high early in the storm, a crust interrupts vertical drainage horizontal drainage, or rain causes liquefaction (a slush avalanche). Many kinds of avalanches can be generated when the total rainfall adds too much weight for a deeper layer to bear.

Thane residents especially will be interested to know that Juneau Mt. Rescue and Eaglecrest Ski Patrol received the latest RECCO units yesterday, and have ongoing training with CBJ to familiarize with new units.