You are here
Avalanche Advisory for 2017-02-02 06:58:48
- EXPIRED ON February 3, 2017 @ 6:58 amPublished on February 2, 2017 @ 6:58 am
- Issued by Nick Meyers - Shasta-Trinity National Forest
Bottom Line
Today, increasing avalanche danger can be expected as a winter storm brings high winds and new snow to the forecast area. The primary concern will lie above treeline as MODERATE avalanche danger this morning will rise to CONSIDERABLE danger this afternoon with the formation of new wind slabs. Expect MODERATE danger near treeline. Below treeline, LOW danger will continue due to lack of significant new snow accumulation and wind.
Avalanche Problem 1: Wind Slab
-
Character ?
-
Aspect/Elevation ?
-
Likelihood ?CertainVery LikelyLikelyPossible
Unlikely -
Size ?HistoricVery LargeLargeSmall
The wind slab avalanche problem today will consist of newly formed slabs from the incoming storm. Moderate to high south/southwest winds are certain and new snow will be available for transport. Slab size will be a function of how much new snow we actually receive. Only 3-5 inches of new snow is expected today, but winds can load leeward slopes 10x faster than snow falling from the sky. Wind slabs are typically most unstable immediately during or just after wind loading events. Expect wind slab sensitivity and size to increase as the storm and wind speeds crescendo over the next 48 hours. Triggering a wind slab this morning is possible and likely this afternoon, near and above treeline. Use visual observations to identify areas of loaded snow, and avoid slopes where evidence of the wind slab problem exists.
Forecast Discussion
Groundhog Day! Punxutawney Phil saw his shadow this morning, predicting six more weeks of winter during Groundhog Day festivities at Gobbler's Knob, a small hill just outside Phil's hometown.
The start gun has been fired and we are off to the races. We have rain and moderate winds currently in Mt Shasta City this morning and snow occuring above 5,000 feet. Instabilities will lie within new snow layers or at the old/new snow interfaces. Southerly flow will dominate and potentially feet of new snow is expected through the weekend in the mountains. Access to the backcountry is still limited with both Castle Lake and Everitt Memorial roads closed. Be careful out there!
Recent Observations
Yesterday, our travels took us out to the East side of Mt Shasta via Pilgrim Creek snowmobile park and into the Ash Creek Butte area. Recent inversions have kept lower elevation snow firm and crusty, especially in the morning hours. Mid and upper elevations became softer with warmer temperatures. Overall, variable snow surfaces exist at all elevations and aspects within the forecast area. A widespread, 1-2 cm crust on southerly, sun effected slopes can be found at most elevations. This crust was supportable in some areas and breakable in others. Shady slopes and/or northerly facing aspects held soft snow still and we thought it was akin to "peanut butter powder". Ridgelines were scoured and icy for the most part. Very small, isolated pockets of light density wind loaded snow was observed on leeward, northerly aspects. A nice looking lenticular cloud was present for most of the day on Mt Shasta, indicating high winds (south/southwest) aloft and likely some decent wind transport of snow on the big mountain. Thus far, the storm is just ramping up... we've seen only .05 inches of precipitation as of this morning, beginning at 2000 hrs last night. There is likely only a trace of new snow in the backcountry this morning. Temperatures are all below freezing at weather stations and southerly flow prevails. While it has been over a week since any significant avalanche activity, this is all going to change as the current storm brings high winds and potentially feet of new snow accumulation over the next several days.
Weather and Current Conditions
Weather Summary
Low pressure spins off the coast of Oregon this morning and begins to make landfall today. Southerly flow is going to prevail for the foreseeable future and bring ample amounts of wet and windy weather. The National Weather Service has issued a winter weather advisory which is in effect until 10am PST Saturday above 5,500 feet. Above normal precipitation and temperatures are expected for the next 6 to 10 days. Winds will gradually crescendo today and tomorrow. Snow levels will be a bit wonky and one can expect mixed rain and snow up to about 6 to 6,500 feet over the course of the storm cycle. In the mountains, we will likely see feet of snow by the end of the weekend. Next week is a bit far out now, but unsettled wintery weather is expected nonetheless. Today, the storm will be at a slow idle... tonight and tomorrow it will start to rev its engines.
===========================================================
In Mt Shasta City at 0500, we have a current temperature of 37 F.
On Mt Shasta (South Side) in the last 24 hours...
Old Ski Bowl - 7,600ft. the current temperature is 25 degrees F. Temperatures have ranged from 25 F to 36 F. Snow on the ground measures 141 inches with a trace of new snow and little settlement.
Grey Butte - 8,000 feet, the current temperature is 24 degrees F. Temperatures have ranged from 23 F to 32 F. Winds have averaged 10-15 mph with gusts to 28 mph, blowing out of the west/northwest until 0900 and then switching to southwest.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,600 feet, the current temperature is 30 degrees F. Temperatures have ranged from 29 F to 41 F. Snow on the ground totals 90 inches with a trace of new snow and little settlement.
Mt Eddy - 6,500 feet, the current temperature is 27 degrees F. Temperatures have ranged from 27 F to 36 F. Snow on the ground measures 74 inches with a trace of new snow and little settlement. Winds have averaged 2 mph with gusts to 17 mph, southwest in nature.
THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 32.28 inches of water, normal is 22.51 inches, putting us at 143% of normal. For the month of February, we have received .02 inches of water, normal is .24, which is 8% of normal. And finally for the year of 2017, we received 11.12 inches of water, normal is 7.30 inches, putting us at 152% 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: | 30 |
| Max. temperature in the last 24 hours: | 38 |
| Average wind direction during the last 24 hours: | W/NW --> SW @ 0900 |
| Average wind speed during the last 24 hours: | 5-10 mi/hr |
| Maximum wind gust in the last 24 hours: | 15-20 mi/hr |
| New snowfall in the last 24 hours: | trace inches |
| Total snow depth: | 88 inches |
Two Day Mountain Weather Forecast
Produced in partnership with the Medford NWS
| For 7000 ft to 9000 ft | |||
|---|---|---|---|
|
Thursday (4 a.m. to 10 p.m.) |
Thursday Night (10 p.m. to 4 a.m.) |
Friday (4 a.m. to 10 p.m.) |
|
| Weather | Snow. Breezy. Chance of precipitation is 90%. | Snow. The snow could be heavy at times. Windy. Chance of precipitation is 100%. | Snow. The snow could be heavy at times. Breezy. Chance of precipitation is 100%. |
| Temperature (°F) | 37 | 28 | 39 |
| Wind (mi/hr) | South 15-20 mph | South 15-20 mph | South 20-25 mph |
| Precipitation SWE / Snowfall (in) | / 3-5 | / 6-10 | / 6-10 |
| For 9000 ft to 11000 ft | |||
| Thursday | Thursday Night | Friday | |
| Weather | Snow. Wind chill values as low as -4. Windy. Chance of precipitation is 90%. | Snow. The snow could be heavy at times. Windy. Chance of precipitation is 100%. | Snow. The snow could be heavy at times. Wind chill values as low as -2. Windy. Chance of precipitation is 100%. |
| Temperature (°F) | 22 | 20 | 20 |
| Wind (mi/hr) | Southwest 35-45 mph | South 3-7 | Southwest 45-55 mph |
| Precipitation SWE / Snowfall (in) | / 3-7 | / 10-15 | / 10-15 |
