Sunday, March 11, 2012

March 11, 2012
 
Forecast valid: Mar. 11th (8:00 am) – Mar. 12th (8:00 am)
AVALANCHE PROBLEM
 
TODAY’S DANGER
MODERATE Considerable where wind affected.
DANGER SCALE
click for danger scale
DANGER TREND: The danger will remain steady with continued north winds through Tuesday.
 
WEATHER: Partly cloudy with highs near 30 in town and 15 F in The Pass. Winds will be from the northeast at 15 to 30 mph near town and gusting to 40 mph. At The Pass winds will be from the North from 30 to 50 mph. Wind Chill Index
 
It will clear off tonight with sun forecast for tomorrow morning before increasing clouds and another chance for snow late Tuesday into Wednesday. GFS Meteogram
 
TRAVEL ADVISORY:  Fresh windslab will continue to form today through The Pass and in channeled terrain and exposed ridge lines near The Port. Commonly Thompson Pass and the Lowe River Valley redirect north winds to load slopes from east to west. 
 
Out of the wind the snow quality is good with the Mar 5-6 storm snow having settled to about 10″ near the port and less than 5″ inland where it has remained loose and dry with no distinct shears.
 
Mild afternoon temperatures around town near 30 F and the chance of extended sun breaks may cause point release avalanches to release on steep, south-facing slopes in lower elevations.
 
AVALANCHES:
  1. Mar 10 – Human triggered D1 slab avalanches reported near Benzene Alley. Size 1 windslab avalanche at MP 20.
  2. Mar 9 – Natural size 1 soft slab avalanche at 2,800ft on convex roll facing west. 
  3. Mar 8 – Human triggered size 1-1.5 wind slab avalanches kicked off on multiple aspects at all elevations.
  4. Mar 7 – Widespread point releases to size size 2, both cold dry new snow running far and also when the new snow was warmed by the sun. Size 2 slab avalanche on a SW shoulder at Mile 60.
  5. Mar 2 – Size 2.5 slab avalanche near 32 mile. Pic 1, Pic 2.
Post your observations <here>.
Avalanches are sized using the destructive scale <here>.
 
 
VALDEZ
 THOMPSON PASS
 24 Hour 
0.1″
0″
March
22″
10″
Season Total
426″
636″
 Base
92″
132″
   
Snow load measured March 4, 2012 by NWS Valdez was 101.4 pounds/square foot. 
 
WEAK LAYERS:
  1. Interface beneath new windslab.
  2. Valentine’s Day near surface facets. Profile.
  3. Feb 6 surface hoar in the intermountain snow climate zone.
  4. Melt freeze layer in low elevations near the port. Francis Profile. Benzene Profile.
CONFIDENCE: Good.
 
Season Summary (written Feb 17) <here>
 
DEFINITIONS:
Snow climate zones:
  1. Maritime (Coastal) – from the Port of Valdez to Thompson Pass, all waters flowing into Valdez Arm and everything south of Marshall Pass.
  2. Inter-mountain (Transitional) – between Thompson Pass and Rendezvous Lodge.
  3. Continental (Interior) – the dry north side of the Chugach (north of 46 Mile, including the Tonsina River).
ELEVATIONS:
Lower – below 1500 feet
Mid – between 1500 and 3000 feet
Upper – above 3000 feet