... WINTER WEATHER ADVISORY UNTIL 9 AM AKST THIS MORNING ...

TODAY ... SNOW CHANGING TO RAIN BY AFTERNOON. SNOW ACCUMULATION TO 4 INCHES. STORM TOTAL SNOW ACCUMULATION 5 TO 7 INCHES. HIGHS AROUND 39. NORTHEAST WIND 5 TO 15 MPH BECOMING SOUTHEAST 15 TO 25 MPH IN THE AFTERNOON.

TONIGHT ... RAIN IN THE EVENING ... THEN RAIN SHOWERS LATE. LOWS AROUND 35. SOUTHEAST WIND 5 TO 15 MPH.

SUNDAY ... RAIN SHOWERS. SNOW LEVEL 1400 FEET. HIGHS AROUND 42.
SOUTHEAST WIND 5 TO 15 MPH.

Winds shifted direction last night to be predominantly out of the the South East, and they picked up to just over 20kts at ridgetop levels. The perfect speed for wind loading new snow.

However, we have not had that much snow so far. Only about 9cm at the Tram where temps are holding right around 0c now, but are expected to climb later in the day.

We might get rain climbing all the way up into our start zones by 3pm this afternoon which is likely to trigger wet avalanches in the new snow. Sizes will be small and are unlikely to come near structures or roads, but will be large enough to cause problems for hikers, dog-walkers, etc along the Flume/Perseverance Trails.

The precip will continue steadily through Sunday night. As snow amounts increase so will the hazard. Main problem will be rain on snow if/when the snow line rises to 2500ft. At this point I don't expect the Urban hazard to rise above Considerable due to lack of large accumulation amounts.

This forecast will be updated by 6pm tonight if the storm starts dropping significantly more snow than predicted.

Avalanche Danger is at MODERATE today: Large natural avalanches unlikely; human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas. Use caution in or under steeper terrain and in avalanche zones.

This forecast is not reflective of backcountry conditions. Backcountry users should employ conservative decision making this weekend, especially regarding lee slopes, complex or high consequence terrain, and unsupported rolls. Persistent weak layers may still exist in protected areas.

Please plan to avoid the Flume and Perseverance trails over the weekend.

Re-posting Peter's Tip as this is the relevant hazard.

RAIN ON SNOW

By tonight we will be seeing warmer, heavier precipitation falling at the higher elevations. This is forecast to transition to rain sometime over the weekend.

Rain can add a huge amount of weight to the snowpack, especially prior to the formation of drainage systems such as runnels. Generally this raises the avalanche hazard early in the event. Wet slab avalanches are associated with these events. Wet slabs have proportionally more mass than dry avalanches, and can be very destructive.

Currently we have a large block of sun-glazed melt-freeze snow which will underlie the new storm snow in starting zones. In many areas there are also chalky wind pockets, and a few protected spots are retaining some dry snow.

Spatial variability for both of these potential bed surfaces is high. These surfaces may provide a poor base for the new snow to bond too, and in some cases liquid water percolating vertically into the snowpack may undermine stability when it hits an impenetrable layer and transitions to horizontal, or ?sheet? flow.

Wind, mixed precipitation types, rising temperatures, and an unusual snowpack. We have a number of red-flag avalanche ingredients for this storm, it will be interesting to see what kind of cake we bake.

Expect the forecasted hazard to change through the weekend.