From the National Weather Service:

Today: Increasing clouds. Snow likely. Snow accumulation 1 to 2 inches. Highs around 33. Northeast wind 5 to 15 mph. Near downtown juneau and douglas...wind increasing to 15 to 25 mph with gusts to around 35 mph in the afternoon.

Tonight: Snow and rain. Snow accumulation 3 to 5 inches. Storm total snow accumulation of 4 to 7 inches. Lows 29 to 35. Southeast wind 15 to 25 mph.

Saturday: Snow and rain becoming all rain in the morning. Rain. Snow accumulation to 2 inches. Highs around 41. Southeast wind 10 to 20 mph.

Temperatures up high stayed around 15f despite the relatively balmy conditions at sea level on what might have been our last day of sunshine for a while. Winds at ridge top elevations calmed somewhat over the last 24 hours, hovering around 25kts.

The NWS has issued a winter weather advisory for this storm. Today we will see minimal accumulation accompanied by moderate gusty northeasterly winds. Tonight the winds will continue along with heavier snowfall, loading our urban start zones. Overnight temperatures will warm significantly; lower elevations will be seeing rain by tomorrow morning.

Wind loading will be occurring in our urban start zones, which have variable bonding conditions, making it difficult for the new snow to paste in. Timing of the warming and actual precipitation amounts will determine the hazard.

The urban hazard remains at LOW today. Light daytime snowfall and slight warming are expected. With low levels of precipitation forecast, the potential for large slides that would come close to urban zones and structures is still very small, however smaller slides are likely to be occurring as the storm develops. Overnight most of the snow will fall along with moderate winds, which may increase the urban hazard. This forecast will be updated by 6pm this evening if trends indicate.

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.

Yesterday we covered how wind affects snow transport and distribution during a storm. Today we will consider rain-on-snow events. NWS has issued a winter weather advisory for this storm (copy and paste):

http://forecast.weather.gov/showsigwx.php
?warnzone=AKZ025&warncounty=AKC110&firewxzone=AKZ025&local_place1=
6+Miles+SE+Snettisham+AK&product1=Winter+Weather+Advisory#.UxnSfOddWTY

By saturday 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 is high. These surfaces may provide poor substrate 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 interesting 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.