From the National Weather Service:

TODAY...RAIN...BECOMING HEAVY AT TIMES. HIGHS AROUND 43. SOUTHEAST WIND INCREASING TO 15 TO 25 MPH IN THE AFTERNOON. GUSTS INCREASING TO 35 MPH IN THE AFTERNOON.

TONIGHT...WINDY...RAIN...HEAVY AT TIMES. LOWS AROUND 37. SOUTHEAST WIND 15 TO 25 WITH GUSTS TO 40 MPH...DIMINISHING LATE.

TUESDAY...RAIN SHOWERS. SNOW LEVEL 1400 FEET IN THE MORNING. HIGHS AROUND 43. SOUTHEAST WIND 15 TO 25 MPH DECREASING TO 5 TO 15 MPH IN THE AFTERNOON.

Over the last 24 hours Mt. Roberts weather plot saw temperatures to 35f. Precipitation was greater than forecast, with 0.55? of mixed rain and snow at the tram. Winds were generally in the teens through the night with a short period of higher intensity yesterday afternoon peaking at 30mph.

The next 24 hours are forecast to be a soaker. Sea level precipitation may reach up to 2.5? accompanied by southeast winds gusting to 40mph and temperatures peaking at 43f. Urban start zones will see mixed precipitation this morning turning to rain by mid-day. Freezing levels are currently at 1500-2000'.

Todays high intensity precipitation will likely create natural wet avalanches. These smaller slides may step down into the deeper but spatially variable persistent weak layer, creating larger avalanches.

Todays urban hazard is HIGH. Natural avalanche activity is probable. Slides should remain small to medium in size. Slides will not likely be capable of reaching structures in the urban start zones.

Stay off the Flume and Perseverance Trails today.

Avalanche runout distance is greatly affected by the physical geometry and character of the runout itself. Any obstacle or rough surface that adds friction to a moving slide acts to slow it down, decreasing the energy. Large vegetation, transverse gullies, knobs, and other terrain features are examples. As these get covered up and smoothed over by the season's snow, the ability to impart friction is reduced. With our starting zones mostly melted out below 1500', there are a lot of these friction-adding features exposed.

Avalanche character is also important when considering the effects of topography on friction. Alders may help slow a smaller slab triggered slide, but will be bulldozed easily by a heavy wet one. Wet slides in particular can flow around and through many obstacles, imparting very high impact pressures in a slow, powerful manner.

For more on wet slides see this great definition:
http://en.wikipedia.org/wiki/Avalanche#Wet_snow_avalanches