Avalanche Advisory
Advisory: Provo Area Mountains Issued by Mark Staples for Saturday - April 7, 2018 - 7:01am
bottom line

Today the avalanche danger is CONSIDERABLE. Rain yesterday and heavy rain today up to 11,000 feet will cause both wet loose and wet slab avalanches.

Most avalanche activity will be wet loose avalanches. However, larger wet slab avalanches may occur as well. It's hard to forecast for wet slab avalanches but they could break 3-6 feet deep and be very destructive.
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current conditions

Since yesterday morning the Provo area mountains received 0.3-0.75 inches of precipiation. By the end of the day, the snow surface was damp up to 10,500 feet. At lower elevations near 8000 feet, the snowpack was saturated and unsupportable.

The rain/snow line this morning is at 9300 feet and mountain temperatures are in the upper 30's F. Westerly winds are averaging 5-10 mph gusting 15-20 mph. The rain/snow line will rise throughout the day with heavy rainfall. See mountain weather at the bottom.

Our Week in Review can be found by clicking here, including coverage of a recent avalanche cycle in the Provo mountains.
recent activity

Yesterday, ski patrols in the Cottonwood Canyons easily triggered shallow, wet avalanches and observed natural rollerball activity. Additionally, they reported that rain had started to saturate the thick, hard ice crusts near the snow surface.
Avalanche Problem 1
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

The snowpack became saturated yesterday afternoon at low and mid elevations, and the snow surface became wet at upper elevations.

Heavy rain up to 11,000 feet will continue to saturate the snowpack and cause wet loose avalanches. The period of greatest instability may be this afternoon when rainfall is heaviest. These will be good triggers for larger deeper slides. See the next section about Wet Slab Avalanches.
Avalanche Problem 2
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

Rain yestereday combined with heavy rain today should cause some large wet slab avalnches. These types of slides are hard to forecast, but we know they are often triggered by small, wet loose avalanches.

Some wet slabs may break less than a foot deep on all aspects within several different ice crust and snow layers that formed during the last week.

Some wet slabs may break much deeper on buried faceted layers. Large avalanches occurred last Wednesday, March 28th on Timpanogos following a wind event. More large slides like those should occur with today's heavy rain. These large slides are more likely on NW, N, NE aspects where buried weak layers mostly exist. Check out this video from the Sawtooth Avalanche Center in Idaho showing what kind of damage wet slabs can do. The photo (J. Woodruff) below shows the debris pile from one of the slides on Timpanogos last week.

HEADS UP - Wet slab avalanches may be hard to predict, but we know they have the ability to run very far downhill, often much further than you'd ever expect.
weather

Today's weather forecast is simple in terms of avalanches. Heavy rain will fall up to nearly 11,000 feet. The rain/snow line is near 9300 feet this morning but will be rising. The heaviest rain should occur this afternoon. By tomorrow morning 1-1.5 inches of rain should fall. At 9000 feet, temperatures should reach the upper 40's F. Winds should increase some as the cold front approache and blow 10-20 mph gusting 30-40 mph from the SW. Unfortunately, the cold front will pass over the area tonight and not much additional precipitation is expected once temperatures start dropping. Only a few inches of snow should fall by early tomorrow morning.

In meteorological terms, this weather event is WAY outside of what is normal. Rain this time of year is normal, but rain at 11,000 feet is not. Jim Steenburgh, University of Utah Atmospheric Sciences Professor, wrote a blog post about this event worth reading. If you don't have time or interest to read his blog, at least look at the graph below. All you need to know is that the red squigly line is the previous record high values for precipitable water. This weather event is the yellow dot and well above that.is well above that.
general announcements

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This information does not apply to developed ski areas or highways where avalanche control is normally done. This advisory is from the U.S.D.A. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.