Avalanche Advisory for Thursday, January 4, 2018

All forecast areas in Huntington Ravine will have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches will be likely during daylight hours. Avalanche danger will rise to High this evening with natural avalanches becoming likely. Dangerous avalanche conditions will exist this afternoon.

Tuckerman Ravine will have HIGH and CONSIDERABLE avalanche danger. Sluice, Lip, Center Bowl, and Chute will have High avalanche danger. Natural avalanches will become likely and human triggered avalanches will be very likely. All other forecast areas will have Considerable avalanche danger. Natural avalanches will be possible and human triggered avalanches likely. The Little Headwall still has open water and is not a recommended route.

DANGEROUS AVALANCHE CONDITIONS WILL DEVELOP THIS AFTERNOON.

AVALANCHE PROBLEM: Wind slabs developing this afternoon will build rapidly and create dangerous avalanche conditions in and below steep terrain. Due to the steepness of most of our terrain and the speed and intensity of new snowfall, it would be extremely challenging to find stable snow among the developing storm slab anywhere in our forecast areas. By late afternoon, expect wind slabs to trend larger and more sensitive to human triggering as wind ramps up and blows across our smaller northern fetch zones. In the evening, natural avalanches could begin running into the floor or lower angled areas of both ravines.

WEATHER: Heavy snow and wind wrapping through the east this afternoon is driving our avalanche rating. New snow totals largely depend on banding and as a result total amounts during the day are followed by a question mark, though 8-12” seems likely by dark. One thing that is certain is the high wind that will accompany this storm as it passes through tonight. Wind speeds through the late morning as snow begins may remain moderate in the 20-35 mph range from the southeast. But peak snowfall in the afternoon will be accompanied by loading velocity winds which will continue to shift towards the north, through the east, and increase. Wind will reach the 50-60 mph range from the NE by nightfall. Temperatures will remain around 10F with light density and easily wind transported snow.

SNOWPACK: Cross-loading of terrain features and start zones will create cohesive slabs on top of weaker, lower density snow. High rated areas are starting out with some soft new snow from some light wind loading that occurred the day before yesterday. These areas seem likely to produce larger avalanches due to this layer, as well as their location downwind of a larger fetch zone. Expect Lobster Claw and Right Gully, which have been lacking snow near the ridgeline, to quickly fill in on this afternoon’s wind, with natural avalanches trending towards likely. As wind shifts further west overnight, more snow will be available to the wind and wind slabs will grow much larger in both ravines. Expect elevated avalanche danger tomorrow, possibly exceeding today’s danger ratings.

The Lion Head Winter Route is the safer route to the summit on the east side. Both the Tuckerman and Huntington Ravine Trails as well as the Lion Head Summer Route pass through several avalanche paths and are challenging mountaineering routes with significant avalanche hazard.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
• Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or Harvard Cabin.
• Posted 8:03 a.m., Thursday, January 4, 2018. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-1-4

Avalanche Advisory for Wednesday, January 3, 2018

All forecast areas in Huntington Ravine have LOW avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Firm and generally stubborn wind slabs are the primary avalanche problem today. These firm slabs have good bridging strength in lots of areas but realize that thin spots, convexities and other trigger points may still be lurking.  Evaluate snow and terrain carefully as you move around the terrain today. You’ll find mostly firm and fairly smooth slabs in terrain that hasn’t seen the scouring or sastrugi building action of the wind. Low rated areas have fewer areas of concern and provide more terrain opportunities to avoid potentially unstable firm wind slabs.

WEATHER: A tenth of an inch of snow fell yesterday after a cloud cap and summit fog enveloped the high peaks in the afternoon. Summit temperatures have risen to a balmy -6F this morning following the protracted arctic cold spell. Today looks like the nicest day to get into our terrain with a high of 3F, clearing skies and westerly winds in the 25-35 mph range. The real weather story lies in the approaching low pressure system. The track of the storm changes with each model cycle but generally closer to shore. It is safe to say that we will see avalanche danger rising, with storm slabs building, through tomorrow with peak natural wind slab avalanche activity likely to occur Thursday evening. Westerly winds will build additional wind slabs Friday but to what extent depends on the amount of total available snow.

SNOWPACK: A mix of surfaces is waiting to receive the new snow, with rough rimed ice crust in some upper start zones, heavily textured sastrugi lower and large smooth wind slabs and sluff piles mid-slope. Minor wind loading has continued off and on through the past several days despite little or no new snow over that time. Between the frigid temperatures and less than ideal skiing conditions in steep terrain, only a few areas of our wind hammered slopes were tested. The slopes that were tested by foot traffic such as the Lip, Sluice and Left did not avalanche in spite of the minor faceting that occurred in our mid-upper snowpack. This is attributable to the strong bridging power and propagation resistance of these firm slabs, the spatially variable bonding surfaces and to some degree, the abundance of anchors still unburied. Given the overall good stability, today would be a reasonable day to move around in most of our terrain using safe travel practices.

The Lion Head Winter Route is the safer route to the summit on the east side. Both the Tuckerman and Huntington Ravine Trails pass through several avalanche paths and are challenging mountaineering routes with significant hazards.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
• Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or Harvard Cabin.
• Posted 7:42 a.m., Wednesday, January 3, 2018. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-1-3

 

Avalanche Advisory for Tuesday, January 2, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. North, Damnation, and Yale gullies have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, Chute, Left, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. Lobster Claw, Right Gully, Lower Snowfields, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: The arctic air parked over our region continues to slow stabilization of slabs deposited over the past week. This factor couples with a highly variable upper snowpack to prevent us from dropping below a Moderate rating for much of our terrain. Areas where the wind slabs formed in the last week are most smooth likely pose the greatest stability concern. Remember that these firm slabs, though stubborn to a human trigger, have the ability to propagate a large fracture and that you are most likely to initiate a fracture in thin areas. We don’t expect snowfall forecasted late today to accumulate and pose a stability concern before dark, but be aware that small and touchier slabs could build overnight.

WEATHER: Our consistent and frigid weather should give way to a change by the end of the day. Snow showers this afternoon and tonight could bring anywhere from a trace to 5” of new snow. Summit temperatures have hovered around -20F for the past 24 hours and will slowly rise today through tonight to reach the positive single digits by tomorrow. NW wind should increase towards 70 mph while shifting W by the end of the day and diminish overnight to summit wind of 30-40 mph tomorrow. Thursday could bring a stronger low pressure system and additional snowfall.

SNOWPACK: Our upper snowpack formed over the past 10 days continues to hold potentially weak layers as cold air inhibits strengthening of bonds. We expect these slabs to remain stubborn though not impossible for a human to trigger. Slab thickness varies greatly, which provides a tricky situation for travel decisions and applicability of stability test results. This spatial variability also means that while low in likelihood, a human triggered avalanche could be large. Facets growing near the December 23rd crust, where it is still present, continue to contribute to the dynamic nature of our snowpack. We haven’t yet seen evidence for this potential weak layer to be particularly reactive or be associated with a strong fracture propagation. It continues to be relevant, though its current low likelihood of producing a sizeable avalanche prevents us from shifting towards persistent slab as our primary avalanche problem. Of equal or greater concern could be new snowfall tonight and potentially again on Thursday.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
• Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or Harvard Cabin.
• Posted 7:30 a.m., Tuesday, January 2, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-1-2

Avalanche Advisory for Monday, January 1, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. North, Damnation, and Yale gullies have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

 Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, Chute, Left, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. Lobster Claw, Right Gully, Lower Snowfields, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: Wind Slabs formed through last week will be slow to stabilize with the cold air that currently dominates our area. The smooth slabs of most concern are fairly firm and can generally be found below the wind textured upper start zones of much of our terrain. Varying in thickness, such slabs are easiest for humans to trigger in thin areas where body weight can more easily impact an underlying weak layer. Remember that it’s difficult at best to visually estimate slab thickness. Though stubborn to a human trigger, a fracture in these hard slabs can propagate a great distance. This characteristic combines with chilling conditions to elevate the consequence of awakening our avalanche problem. As a secondary concern, keep softer slabs that will be significantly more isolated but of greater sensitivity to a trigger on your radar.

WEATHER: We’re ringing in the New Year but our weather is remaining largely the same. 60-70 mph wind and a high temperature of -13F on the summit made yesterday feel the most frigid of recent days despite inviting blue skies. Today NW winds will slightly reduce in speed to around 50 mph and the mercury will remain in the teens below zero with mostly sunny skies. Tuesday morning looks to be slightly more pleasant, with wind slackening a bit and air temperatures creeping another 10 degrees higher. Wind is forecast to elevate as is sky cover by the end of the tomorrow. Don’t expect to see measurable precipitation until later in the week when a low pressure system could impact our region, bringing snowfall and generally less arctic conditions.

SNOWPACK: You’ll find a mixed bag of surface conditions with large smooth slabs remaining if you venture into our terrain today. Motivated and savvy travelers could lessen exposure to today’s primary avalanche problem by sticking to heavily textured snow and exposed old crust. Our concern for facet growth in the upper snowpack will elevate the longer this very cold air remains in place. Snow pits should yield interesting results anywhere above tree line, with varying density wind slabs existing above and below the December 23rd crust. A variety of wind speeds and direction as well as natural avalanches since our last significant snowfall on Christmas have made for significant spatial variability in our upper snowpack. Do dig pits, but remember that their results will not tell the whole story for a particular slope.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
• Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or Harvard Cabin.
• Posted 7:30 a.m., Monday, January 1, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-1-1