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Avalanche Advisory for 2017-02-08 07:06:25
- EXPIRED ON February 9, 2017 @ 7:06 amPublished on February 8, 2017 @ 7:06 am
- Issued by Nick Meyers - Shasta-Trinity National Forest
Bottom Line
Wind slab, loose-wet/wet slab and cornice problems are expected today and overall, CONSIDERABLE avalanche danger. High wind and flood warnings are in effect through Thursday evening. Several inches of rain on snow up to 8,500 feet and high intensity snowfall above this elevation is expected over the next 48 hours with gale force winds out of the south. Be aware of avalanche run out zones and the potential for large avalanches coming from above.
Avalanche Problem 1: Wind Slab
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High intensity snowfall and gale force southerly winds are in the forecast over the next 48 hours for above treeline terrain. Existing wind slabs are already hard, stiff and several feet thick and will continue to grow as heavy, wet snow adds size and depth. Wind slabs could be triggered in terrain above 8,500 feet and have the potential to be large and destructive with the possibility of reaching low angle run out zones. Stay clear of avalanche paths that extend below treeline and stay off slopes steeper than 35 degrees where evidence of the wind slab problem is observed.
Avalanche Problem 2: Loose Wet
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Snow levels will rise to 8,500 feet today. Several inches of rain is forecasted to fall over the next 48 hours. Rain on our snowpack has the potential to cause loose wet instabilities and in some areas may trigger wet slab avalanches, both problems on all aspects. Any layers within the recent storm snow could produce loose wet or wet slab avalanche problems. These types of avalanches, even relatively smaller slides, can be very destructive due to the increased mass of the water within the snowpack. Avoid travel on or beneath slopes where natural roller ball action or signs of loose wet avalanches exist.
Avalanche Problem 3: Cornice
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Small to large cornice features exist on many ridgelines throughout the advisory area. The cornice formations in the Eddy Range have been especially large and impressive. Recent snow accumulation and wind transport are adding weight to existing cornices, and building new cornice features. Cornices are often overhung and can break in very unpredictable ways. If cornices fail, they pose a significant risk of triggering slopes below. Be sure to stand back on ridgelines, and avoid traveling in avalanche terrain threatened by cornice hazard from above.
Forecast Discussion
It's safe to say that most riders and glilders won't be playing in the backcountry due to limited access and very high snow levels... but if you do, bring your best wet weather gear and also your best avalanche game. Ample new snow and rain on snow is in the forecast and will create a host of avalanche problems. Winds are looking extremely high as is the precipitation forecast. Considerable avalanche danger will prevail with potentially periods of high danger later in the day as the storm builds. Be safe out there.
Recent Observations
Temperatures are rising this morning with that 8,500 foot snow level in sight. Unfortunately, I think we will meet that forecast. We received very little new snow over the past 24 hours below 7,500 feet with mostly rain on snow reporting from our weather stations. At upper elevations, 5-10 inches of new snow is possible as Mt Shasta City recorded an inch of water since yesterday morning. Above 6,500 feet is where the majority of recent snowfall has been occurring. Below 4,500 feet has been all rain and in between, mixed. Rain runnels dominate up to 5,500 feet. The Old Ski Bowl has received upwards of 40 inches of snow in the last 6 days and over 4 inches of water.
Yesterday, observations were made in the Castle Lake and near tree line area on Mt Shasta, in the lower Old Ski Bowl area. On the west side in the Castle Lake area, multiple natural loose wet avalanches triggered shallow storm slabs on north/northeast facing slopes, about 6,000 feet. Existing wet and heavy snow failed on a density change. This is typically the case when we have "upside down" layering in the snowpack... heavier snow on top of lighter density snow. Medium to large cornices were also observed along the ridgeline of Middle Peak, Castle Lake area. (See additional pictures and description in observations below)
On the mountain, a group of local riders were able to bust trail up the power lines to the Lower Old Ski Bowl area. Only informal observations were made, like digging in the snow to free stuck snowmobiles. They noted very deep, wet, unsconsolidated snow and were unable to get good visibility of the upper mountain. Already this morning, we've seen 3-5 inches of settlement within the snowpack due to rain on snow and warming temperatures.
An additional avalanche was observed from afar and occurred recently on a westerly facing aspect off Casaval Ridge down into Hidden Valley. Further, a report came in from Little Glass mountain out east of Mt Shasta where a snowmobile rider triggered an avalanche and was buried up to his neck. The group of unknown size had no avalanche rescue equipment other tham one shovel between all of them.
Weather and Current Conditions
Weather Summary
Hold on to your hats and get out your PFD!... this morning marks the start of a downright tropical storm and the NWS has issued flood warnings and high wind warnings for South Central Siskiyou County. Over the next 48 hours, upwards of 3.5 inches of water is forecasted to fall over the Mt Shasta area.... and what really breaks our heart is the 8,500 foot snow levels associated with this storm. I'd love to cry a river, but that will only exacerbate things. Indeed flooding is going to be an issue with ample rain on snow. Wind speeds are expected to be in the top 1 percentile along the coast for this time of year. Inland on the mountain, wind speeds of 70-80 mph are showing on forecast models. Yikes! After the deluge this week, a cold front follows and is supposed to bring snow levels down to near 3,000 feet, but precipitation will diminish by then. The weekend promises to dry out a bit and allow rivers and streams to shed some water.
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In Mt Shasta City at 0500, we have a current temperature of 43 F.
On Mt Shasta (South Side) in the last 24 hours...
Old Ski Bowl - 7,600ft. the current temperature is 27 degrees F. Temperatures have ranged from 26 F to 33 F. Snow on the ground measures 178 inches with 2 inches of new snow and little settlement.
Grey Butte - 8,000 feet, the current temperature is 26 degrees F. Temperatures have ranged from 25 F to 32 F. Wind have averaged 20-30 mph with gusts to 64 mph, blowing westerly in nature.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,800 feet, the current temperature is 33 degrees F. Temperatures have ranged from 31 F to 40 F. Snow on the ground totals 102 inches with no new snow and 4 inches of settlement.
Mt Eddy - 6,500 feet, the current temperature is 30 degrees F. Temperatures have ranged from 29 F to 35 F. Snow on the ground measures 97 inches no new snow and 4 inches of settlement. Winds have averaged 2 mph with gusts to 14 mph, blowing out of the south/southeast.
THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 36.0 inches of water, normal is 23.97 inches, putting us at 150% of normal. For the month of February, we have received 2.74 inches of water, normal is 1.70, which is 220% of normal. And finally for the year of 2017, we received 14.84 inches of water, normal is 8.76 inches, putting us at 169% of normal.
Always check the weather before you attempt to climb Mt Shasta. Further, monitor the weather as you climb. Becoming caught on the mountain in any type of weather can compromise life and limb. Be prepared.
0600 temperature: | 32 |
Max. temperature in the last 24 hours: | 37 |
Average wind direction during the last 24 hours: | Westerly |
Average wind speed during the last 24 hours: | 10-15 mi/hr |
Maximum wind gust in the last 24 hours: | 20 mi/hr |
New snowfall in the last 24 hours: | -4" (rain on snow) inches |
Total snow depth: | 111 inches |
Two Day Mountain Weather Forecast
Produced in partnership with the Medford NWS
For 7000 ft to 9000 ft | |||
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Wednesday (4 a.m. to 10 p.m.) |
Wednesday Night (10 p.m. to 4 a.m.) |
Thursday (4 a.m. to 10 p.m.) |
|
Weather | Rain and snow, becoming all rain after 10am. High near 42. Windy. Chance of precipitation is 100%. | Rain. The rain could be heavy at times. Windy. Chance of precipitation is 100%. | Rain before 4pm, then rain and snow showers. The rain could be heavy at times. Windy. Chance of precipitation is 100%. |
Temperature (°F) | 42 | 37 | 40 |
Wind (mi/hr) | South 15-20 mph | South 20-25 mph | South 25-30 mph |
Precipitation SWE / Snowfall (in) | / 0 | / 1-2 | / 0-.5 |
For 9000 ft to 11000 ft | |||
Wednesday | Wednesday Night | Thursday | |
Weather | Snow. The snow could be heavy at times. Windy. Chance of precipitation is 100%. | Snow. The snow could be heavy at times. Very windy. Wind chill values as low as -2. Chance of precipitation is 100%. | Snow. The snow could be heavy at times. Very windy. Wind chill values as low as -4. Chance of precipitation is 100%. |
Temperature (°F) | 28 | 25 | 26 |
Wind (mi/hr) | Southwest 50-60 mph | Southwest 8-10 | South 70-80 mph |
Precipitation SWE / Snowfall (in) | / 8-10 | / 12-15 | / 15-20 |