Avalanche Advisory for Wednesday, December 27, 2017

This advisory expires at Midnight.

Huntington Ravine has MODERATE avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible in all forecast areas. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully.

 Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential. Lobster Claw, Right Gully, Left Gully and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Lower Snowfields and Little Headwall in Tuckerman have Low avalanche danger due to lack of a developed snowpack. Watch for unstable snow on isolated terrain features such as Dead End and Duchess above the Lower Snowfields.

AVALANCHE PROBLEM: Wind slabs exist through the terrain today following 11” of new snow in the past 48 hours. Sustained 60 mph westerly wind continued to load new snow into our avalanche start zones yesterday and will likely continue to do so today as they are now. Expect a mix of densities in these slabs from finger hard and stubborn to four finger and more sensitive to triggering. Considerable rated areas have a history of prolonged wind loading due to available snow in a W or NW wind so remain elevated today. Natural avalanches are a little more unlikely than possible but careful assessment and snowpack evaluation would be required to confirm. Our slopes continue to grow in area, creating the opportunity for larger avalanches. If you plan to brave the cold today to climb or ride in the Ravines, bring your A game.

WEATHER: The cold temperatures that are making headlines will make for challenging conditions on the mountain today. It is currently -23F on the summit with winds from the west in the low 70 mph range. Temperatures will warm slightly as wind diminish a bit today before plummeting again tonight as wind from the NW increase to near 100 mph. That ugly sweater that was too much for Christmas may be just right today.

SNOWPACK: The summit recorded 1.5” in the past 24 hours. The new snow added to the wind loading that has occurred in the past 48 hours following 9” that fell on the 25th. Limited visibility denied us a view of the upper start zones in Huntington and the bowl in Tuckerman but did allow some other avalanche observations. As expected, the ice crust encasing the 9” of snow that fell on the 22nd/23rd broke down and contributed that snow to the most recent avalanche cycle. This allowed Hillman’s Highway to avalanche around the corner, and Central, Odell’s and South to push pretty far towards the floor. It seems likely that other forecast areas avalanched as well but limited visibility has made closer observations unsafe.

The Lion Head Winter Route is open and the preferred route to the summit from the east side. Remember that natural or human-triggered avalanches can run out onto the floor of Tuckerman Ravine. Keep a safe distance if hiking up to have a look around.

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 the Harvard Cabin.
• Posted 8:05 a.m., Wednesday, December 27, 2017. 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

2017-12-27

Avalanche Advisory for Tuesday, December 26, 2017

Huntington and Tuckerman Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. Lower Snowfields, and Little Headwall in Tuckerman are the exception with Moderate avalanche danger due to a less developed snowpack. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions on specific terrain features.

 AVALANCHE PROBLEM: Yesterday’s snow and wind has built wind slabs over much of our terrain that will vary in hardness and sensitivity. Wind transport is still occurring and will continue for any snow that falls today. Accordingly, our surface wind slabs will continue to change in distribution, size, and character through the day. If you brave cold and wind today you will likely find at least some areas of greater stability, but the dynamic nature of our current surface snow will combine with compromised visibility to make safe travel in avalanche terrain challenging.

 WEATHER: Our Christmas day storm brought 9” of new snow to the summit. W wind in the 60-90 mph range has dominated since yesterday afternoon and will continue today. Show showers today bringing up to 4 more inches of snow which will alternate with occasional partial clearing. Current temperatures in the negative single digits F should steadily creep down through tomorrow morning. The summit will approach -30F. Windchill values could bottom out near -80F. Remember, small problems quickly turn into big problems in this weather. As always, consider the realistic consequences of something going wrong.

SNOWPACK: Poor visibility limits our ability to make observations this morning, though we expect our snow surface is comprised of a variety of firm to very firm wind slabs, with pockets softer snow and exposed crust. The extended summit wind over 80 mph yesterday and forecast to remain high today will have easily transported and compacted much of the low density new snow. The potential for additional snow up to 4” today should be similarly transported. The high density wind slabs we see following these wind events is often supportable and heavily textured on the surface. Such slabs should be stubborn to a human trigger, but the pockets of softer and smoother snow that we skiers and riders seek will be more sensitive in all but select locations. Further, we still expect avalanches to break up the crust formed a few days ago and entrain softer snow beneath it. Below this crust and softer snow, widespread hard slabs that would likely take a massive load to trigger limit our concerns for deep instability. We likely had a widespread avalanche cycle in the last 24 hours, evidence of which we may or may not see today with limited visibility and active reloading of these same avalanche paths.

The Lion Head Winter Route is open and the preferred route to the summit from the east side.

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 the Harvard Cabin.
• Posted 8:00 a.m., Tuesday, December 26, 2017. 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

2017-12-26

Avalanche Advisory for Monday, December 25, 2017

Huntington Ravine has HIGH and CONSIDERABLE avalanche danger. Central, Pinnacle, Odell, and South Gullies will reach High avalanche danger. Natural avalanches likely and human triggered avalanches very likely. Travel in avalanche terrain is not recommended. All other areas in Huntington will reach Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely.

 Tuckerman Ravine has HIGH avalanche danger. Natural avalanches likely and human triggered avalanches very likely. Travel in avalanche terrain is not recommended. Lower Snowfields and Little Headwall in Tuckerman are the exception with Moderate avalanche danger due to a less developed snowpack. Heightened avalanche conditions on specific terrain features.

 AVALANCHE PROBLEM: Today’s significant storm snow and wind will build reactive wind slab over terrain lee to W and NW wind and crossload other aspects by this evening. Lighter winds this morning coupled with heavy snowfall could allow a less cohesive storm slab to briefly develop. Before this becomes much of a concern, wind speeds will rise and build the more cohesive and reactive slabs that are our primary avalanche problem. Instability will likely peak this evening before sustained extreme wind overnight scours many areas and builds firmer and more stubborn slabs. There is a strong chance that avalanches today will break up Saturday’s crust and entrain soft snow below, resulting in a larger slide than surface slabs might suggest. Areas not receiving a High danger rating today lack the snowpack development to produce a large avalanche, though the likely but smaller human triggered avalanches in these areas could still have dire consequences.

 WEATHER: We’re all getting a heap of snow for Christmas! It’s coming down already and by tomorrow we will likely have over a foot of new snow on the mountain, with heaviest snowfall earlier in the day today. Southerly wind in the mid-30’s mph range during the heaviest precipitation will increase and shift through W to NW as snowfall tapers but continues through today and tonight. Sustained wind speeds over 70 mph with gusts nearing 100 mph can be expected. Summit temperatures will trend downwards from single digits above to single digits below zero. Light snow will continue tomorrow as W to NW wind continues to push the century mark. This weather follows a major crust building event on Friday and a subsequently unremarkable Christmas Eve. Limited snow was available for wind transport yesterday, but plenty will be today.

SNOWPACK: Today’s storm will be deposited on a layer of 1-2 cm breakable crust that formed Friday evening and exists on most of our terrain. The snow that fell earlier on Friday remains soft and dry beneath this crust. We expect avalanches today to occur above the crust, but realize that any sizable avalanche will break up this crust and entrain Friday’s storm snow below it. The avalanches that are likely to occur today will likely be large relative to current path development. It’s a great day to recreate in the snow without exposing yourself to avalanche terrain. The John Sherburne Ski Trail now has good coverage and should ski well as the new snow accumulates!

The Lion Head Winter Route is open and the preferred route to the summit from the east side.

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 the Harvard Cabin.
• Posted 8:00 a.m., Monday, December 25, 2017. 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

2017-12-25

Avalanche Advisory for Sunday, December 24, 2017

Huntington and Tuckerman Ravines have MODERATE avalanche danger. All forecast areas have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully to identify features of concern. Lower Snowfields and Little Headwall in Tuckerman are the exception with Low avalanche danger due to lack of a developed snowpack. Natural and human triggered avalanches are unlikely there.

 AVALANCHE PROBLEM: Previously existing wind slab and sluff piles beneath steep features were encased in ice yesterday afternoon. A brief visit to Hillman’s this morning in low visibility conditions revealed that you could find, and posthole into, areas of soft, dry snow beneath a glaze of ice in lots of areas. One of the concerns that would be on my radar today would be some of the large piles of sluff sitting beneath funnel points in our steepest terrain. An outside chance of perforated the ice and being the trigger on one of these wind slab/sluff piles would be enough to keep me from traveling alone or leaving my beacon, probe and shovel in the car. Additionally, light snow fall continues this morning and may build small wind slabs in lee areas.

 WEATHER: It should be no secret that we saw a mixed bag of precipitation yesterday. At Hermit Lake, around 5” of snow fell before the storm switched over a crust building rain and frozen precipitation mix in the afternoon. Temperatures hovered just below freezing with southerly wind around 40 mph through the bulk of this storm. Precipitation tapered off overnight, summit temperature dipped to the current single digits above zero F, and wind shifted through W to NW increasing to the current 70 mph. Today’s break between storms should be accompanied by temperatures in the teens, mostly cloudy skies, and a wind that will eventually decrease as it shifts through W and S to SE as snowfall begins tonight. A significant storm in the next 36 hours looks to bring a storm total of around a foot of new snow on southerly wind that will shift NW and elevate as snowfall tapers off. It certainly looks like a white Christmas!

SNOWPACK: A breakable freezing rain crust of 1-2 cm thickness is our primary surface from the lower mountain up to the floor of the ravines. We believe that this crust is pervasive through our upper terrain, though visibility limits our current ability to confirm this. Beneath this crust formed yesterday afternoon much of our terrain will hold the comparatively dry snow that fell prior to crust formation. This snow will vary in thickness from several inches to more than a foot. Though you would be hard pressed to trigger an avalanche today in this snow it will likely be a player in tomorrow’s avalanches. The significant snow and wind coming Monday could produce avalanches on this crust that would ultimately break it apart and entrain the soft snow below.

The Lion Head Winter Route is open and the preferred route to the summit from the east side. Daylight hours are short today…don’t forget to adjust your turn around time and headlamp. Expect to posthole into soft snow beneath the crust if travelling off the beaten path.

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 the Harvard Cabin.
• Posted 8:00 a.m., Sunday, December 24, 2017. 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

2017-12-24

Avalanche Advisory for Saturday, December 23, 2017

Huntington and Tuckerman Ravine have CONSIDERABLE avalanche danger. All forecast areas have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential. Lower Snowfields and Little Headwall in Tuckerman have Low avalanche danger due to lack of a developed snowpack. Natural and human triggered avalanches are unlikely there. Watch for unstable snow on isolated terrain features such as Dead End and Duchess above the Lower Snowfields.

AVALANCHE PROBLEM: New snow yesterday created some wind slabs throughout the terrain. These slabs were built from low density snow on light to moderate winds and will remain touchy this morning. Furthermore, this snow comes with a lump of coal in your stocking. Warming temperatures, sleet and possibly a bit of rain will begin to load the new snow and wind slabs making them even more sensitive to a human-trigger and increasing the likelihood of natural avalanches. There are enough areas of softer snow from earlier in the week so it’s possible that an avalanche could entrain more snow than just yesterday’s snowfall. If you survive the freezing rain glazed roads to get to the mountain, you’ll have your hands full staying safe due to this mix of avalanche problems!

WEATHER: Snow will continue this morning before warm air overriding cold air at ground level brings sleet, then freezing rain to all elevations.  We may even see a greater variety in precipitation types, including plain old rain, as today’s weather brings nearly 0.5” water. Wind should remain moderate out of the S to SW through daylight hours. As precipitation winds down tonight, expect wind to shift to W then NW and increase to around 60 mph. This wind is forecast to continue through tomorrow, when we will also see a break in precipitation, partial cloud cover, and temperatures back down into the teens.

SNOWPACK: In the past 24 hours, the snowplots at 3800’ recorded around 15cm of 5.5% density snow with 8” recorded on the summit. Steady light to moderate snow (S-1 to S1) fell through yesterday starting at around 9am. The low density snow provided lots of good skiing on lower angled areas low in Left and Hillman’s and in Huntington. All parties wisely avoided the steeper, and more wind loaded upper start zones where loading was happening and some instabilities lingered from previous snow this week. As is often the case with light snow in steep terrain, dry loose avalanches, a.k.a. sluffing, occurred and was reported to be sizeable in Yale Gully in the afternoon. This recent avalanche activity highlights the potential danger today.

The Lion Head Winter Route is open and the preferred route to the summit from the east side. Daylight hours are short today…don’t forget to adjust your turn around time and bring your headlamp!

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 the Harvard Cabin.
• Posted 8:00 a.m., Saturday, December 23, 2017. 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

2017-12-23

Avalanche Advisory for Friday, December 22, 2017

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. Heightened avalanche conditions will exist on specific terrain features. Evaluate snow and terrain carefully. North, Damnation and Yale Gullies have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

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

AVALANCHE PROBLEM: New wind slabs are the primary avalanche problem today. 3-5” of new snow will likely be blown into relatively thin but potentially reactive wind slabs in areas lee of a light southeast wind. Additionally, anticipate dry loose avalanches or sluffing from steep terrain. This will build piles of sluff debris which behave as a wind slab. Both of these problems will develop later in the day. The size and ease of triggering of these avalanches is highly dependent on localized wind speed and direction. Summit wind speeds are generally much higher than those in our start zones so assess conditions carefully through the day. The likelihood and size of a natural or human-triggered avalanche will increase through the day and push the avalanche danger up, especially after dark as snow continues.

WEATHER: Light snowfall has begun on the summit this morning. Snowfall will begin at lower elevations as the cold, dry air in place begins to saturate. The current temperature on the summit is 6F with a light west wind at 22 mph. Temperatures will rise to the lower teens F as winds shift to the southwest by nightfall. Expect 3-5” of new snow by the end of the day. Visibility will be reduced as summit fog builds through the day.

SNOWPACK: Successive Canadian clippers this week delivered 19” of snow (2.23” water) to the higher terrain since Sunday. Thursday, signs of natural avalanches were observed in Hillman’s, Pinnacle, Odell and possibly high in the exit of Damnation. These areas likely slid Wednesday. Field work yesterday in Tuckerman showed that this snow was hammered by wind on Wednesday and early Thursday. The currently firm and heavily textured surface snow should form a reasonably good bonding interface for new snow today in all but the steepest areas. As noted above, expect avalanche danger to rise through the night and anticipate elevated danger tomorrow as snow continues and then turns wetter as temperatures warm. Wet snow or sleet will likely overload the new dry snow during the day tomorrow.

Due to this week’s snow filling things in and expanding the start zone on the Lion Head Summer trail, the Lion Head Winter Route is open and the preferred route to the summit from the east side. The John Sherburne Ski Trail will be great skiing today but there are still rocks in the usual wind scoured areas that will be barely submerged by new snow. Daylight hours are short today…don’t forget to adjust your turn around time!

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 the Harvard Cabin.
• Posted 8:00 a.m., Friday, December 22, 2017. 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

2017-12-22

Avalanche Advisory for Thursday, December 21, 2017

This advisory expires at Midnight.

Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, and Odell gullies have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other areas have Low avalanche danger. Natural avalanches and human triggered avalanches are unlikely.

Tuckerman Ravine has Considerable, Moderate and Low avalanche danger. Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation and cautious route-finding are essential. Right Gully, Sluice, Left Gully, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Lobster Claw, Lower Snowfields and Little Headwall have Low avalanche danger due to limited snowpack development. Natural and human triggered avalanches are unlikely.

AVALANCHE PROBLEM: Wind slab remains the primary avalanche problem. The 10” of snow that has fallen in the past two days has been moved into our terrain and created a mix of stability ranging from fair to good. Some of these slabs are thick and would result in an avalanche large enough to carry and bury you. Beware of smooth pillows of wind slab beneath steep features and in the most sheltered lee terrain. Mixed in the more recent wind slabs are layers of heavily rimed snow grains which tend to be slow to bond and stabilize. Wind loading is continuing this morning and is a player in areas with elevated danger.

WEATHER: The temperature this morning on the summit has rebounded a bit to -4F from a low of -8F. Temperatures will warm under clear skies with good visibility and reach around 5F. Wind will diminish through the day to the 35-50 mph range from the NW on the summit. Winds in the 60-75 mph range, predominately from the WNW in the past 36 hours, moved the last 3 days snowfall into the Ravines. Today’s winds are unlikely to find more snow to transport into our start zones. More precipitation is on the way for the weekend so stay tuned.

SNOWPACK: The successive Canadian clippers this week delivered 19” of snow (2.23” water) to the higher terrain since Sunday. Combined with strong winds, this snow built wind slabs in many areas throughout our terrain. Field work in Huntington Ravine on Tuesday revealed that more recent new snow built thick slabs beneath steep features due to sluffing with softer and more reactive layers near the surface and in well protected lee areas. Deeper down in the snowpack, the slabs built by the 16” storm on the 11th/12th have proven to be unreactive, despite sitting on a melt freeze crust from warming that occurred on the 4th/5th of December. The relative stability is likely due to a period of freezing rain on the 19th combined with the stabilizing influence of time along with the bridging power of strong slabs. Our snowfall this week has been light to moderate without the howling winds that quickly build unstable slabs which fail under their own weight. Crown lines and debris exist in Central Gully indicating that a natural avalanche occurred there. That said, move carefully in the terrain today since the fresher wind slabs could still be triggered on foot or ski.

Due to this week’s snow filling things in and expanding the start zone on the Lion Head Summer trail, the Lion Head Winter Route will likely be open by the weekend. Coverage on the John Sherburne Ski Trail continues to improve but there are still rocks barely submerged by new snow.

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 the Harvard Cabin.
• Posted 8:15 a.m., Thursday, December 21, 2017. 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

2017-12-21

 

Avalanche Advisory for Wednesday, December 20, 2017

This advisory expires at Midnight.

Huntington Ravine has Considerable and Moderate avalanche danger. Central, Pinnacle, and Odell gullies have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

 Tuckerman Ravine has High and Considerable avalanche danger. Lip, Center Bowl, and Chute have High avalanche danger. Natural avalanches are likely and human triggered avalanches are very likely, travel in avalanche terrain not recommended. Right Gully, Sluice, Left Gully, and Hillman’s Highway have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Lobster Claw, Lower Snowfields and Little Headwall lack snowpack development.

AVALANCHE PROBLEM: Another good shot of new snow on westerly winds gives us Wind Slab as a primary avalanche problem. This slab will vary in density and reactivity to a human trigger across varied terrain. Areas receiving the heaviest deposition will hold the largest and most reactive slabs which could avalanche naturally. Terrain that has seen lighter loading will likely hold softer slabs that will be sensitive to a human trigger.

 WEATHER: After yesterday’s 5” of new snow on W wind around 50 mph, a very brief break in the weather was followed by up to 8” of snow on increasing W wind that held near 70 mph for several hours. Temperatures held near 20F during the bulk of this snowfall. Today, snowfall should taper off to at least a partial clearing while wind shifts NW and slackens slightly to around 50 mph on the summit. Temperatures will return to their more seasonable single digits on the summit today and tomorrow, with no further precipitation in the coming 36 hours.

SNOWPACK: It’s full on winter, complete with a dynamic snowpack. While paths like Lobster Claw lack snowpack development, others have already seen multiple natural or human triggered avalanches. Today’s avalanche problem compounds yesterday’s similar density wind slab, giving us at least two distinct layers that seem to be behaving independently above the older firmer snow. In addition to slab characteristics driven by wind transport and deposition, look for cohesion and density that was driven by varying temperatures and particle forms over the past 48 hours. In particular, we observed a reactive though relatively thin layer of rimed new snow particles at the surface around midday yesterday, which has the potential to be overlaid with new wind slab. While difficult to call any potential avalanche today truly “large”, avalanches to the full extent of current path development are likely.

The summer Lion Head Trail is the safer route to the summit than trails through Tuckerman and Huntington. The Lion Head Winter Route will open when snow fills in avalanche paths on the summer trail and fills in the winter route enough to cover rocks, mud and bushes. Coverage on the John Sherburne Ski Trail continues to improve but there are still rocks barely submerged by new snow.

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 the Harvard Cabin.
• Posted 8:45 a.m., Wednesday, December 20, 2017. 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

2017-12-20

Avalanche Advisory for Tuesday, December 19, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravines have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. The only exception to this rating is the Little Headwall, which still lacks significant snowpack development. It is rated Low for the possibility of small avalanches in isolated terrain.

 AVALANCHE PROBLEM: Newly formed Wind Slab that will be soft and reactive to a human trigger this morning is our primary avalanche problem. New snow in the past 24 hours on a consistent W wind has and is still loading our terrain. Continued and increasing wind through the day has the capacity to further decrease stability. We expect areas not yet reaching today’s Considerable danger rating to reach Considerable later today. Areas experiencing the greatest loading could surpass this rating by the time this advisory expires at midnight.

 WEATHER: The summit and much of our terrain has received at least 5” of snow in the past 24 hours on a consistently W wind hovering near 50 mph. We are currently seeing a brief lull in precipitation before snowfall begins again on increasing W wind that should shift NNW and gust to around 100 mph by tomorrow morning. Temperatures will remain at least a few degrees below freezing. Forecast snowfall totals are mixed, so we’re expecting new snow in the 3-10” range in the coming 24 hours.

SNOWPACK: This morning’s relatively soft wind slab problem will be most pronounced on aspects lee to a W wind, where a thinner slab formed Sunday into Monday exists that is similar in density. Wind transport continues currently. Remember that wind deposits can easily quadruple actual snowfall totals, or more. We expect this layer to be quite reactive to a human trigger. Natural avalanches are possible as wind ramps up through the day, and by tomorrow morning we’ll likely see these new slabs largely eroded and/or hardened by this wind. Beneath these softer surface slabs, our more developed paths hold firm (1F+) snow that is not likely to pose a stability concern. Less developed paths will hold a mix of hard and soft snow, rocks, ice, and vegetation beneath the recent deposits. With many hazards exposed or thinly veiled, realize that the consequences of capture by an avalanche remain in an elevated early season state.

The summer Lion Head Trail is the safer route to the summit than trails through Tuckerman and Huntington. The Lion Head Winter Route will open when snow fills in avalanche paths on the summer trail and fills in the winter route enough to cover rocks, mud and bushes. Coverage on the John Sherburne Ski Trail continues to improve but there are still rocks barely submerged by new snow. We love to ski, and we haven’t yet skied it.

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 the Harvard Cabin.
• Posted 8:20 a.m., Tuesday, December 19, 2017. 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

2017-12-19

Avalanche Advisory for Monday, December 18, 2017

This advisory expires at Midnight.

Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, and Odell have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions on specific terrain features; Evaluate snow and terrain carefully. North, Damnation, Yale, South, and Escape Hatch have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

Tuckerman Ravine has Moderate and Low avalanche danger. Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions on specific terrain features; Evaluate snow and terrain carefully. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Evaluate snow and terrain carefully.

 AVALANCHE PROBLEM: Wind Slab formed from snow fallen since Saturday is our primary avalanche problem today. Deposited by wind blowing from the W through NW, this layer is varied in size and distribution across lee terrain. New snow falling later today will contribute to the building of these slabs. Key to your terrain management decisions will be the ability to differentiate between this relatively soft and smooth slab from the firm wind slab formed earlier last week. This older firm layer is present at the surface in many areas and could present a secondary avalanche problem in thin and/or less dense pockets, though it largely provides a more stable surface to travel on.

 WEATHER: Yesterday’s clear skies and moderate NW wind are giving way to the first in a series of fast moving winter storms impacting our area this week. Today, summit temperature will climb to around 20F as an inch or more of snow falls on 30 mph W wind possibly increasing to 50 mph by tonight. Snowfall totals and timing forecasts for today vary. We may see 6” by tomorrow morning with the bulk of the snow falling after dark. Watch for an outside chance of that heavier snowfall arriving before the end of the day. Snowfall will taper though continue in light amounts as W wind increases towards the century mark tomorrow.

SNOWPACK: Significant snowfall in the past 11 days dramatically increased our coverage and snowpack. Our typical extreme winds from the NW followed both major storms creating wind slabs that are relatively dense. In many areas these older and firmer slabs are stubborn to a human trigger. However, a variance in bed surfaces and characteristics of these slabs exists through the terrain and should remain relevant in your snowpack observations.  Our greater concern today is the softer and more recent wind slab discussed above. If snowfall totals push the upper and of the forecast and moderate to strong winds hold through tomorrow morning, we could see an increase in avalanche hazard for tomorrow morning.

The summer Lion Head Trail is the safer route to the summit than trails through Tuckerman and Huntington. The Lion Head Winter Route will open when snow fills in avalanche paths on the summer trail and fills in the winter route enough to cover rocks, mud and bushes. The John Sherburne Ski Trail has improved but there are still rocks barely submerged by new snow and wind scoured bare areas.

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 the Harvard Cabin.
• Posted 7:30 a.m., Monday, December 18, 2017. 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

2017-12-18