Mammoth Mountain Ski Patrol 2009-10 Storm Summary - Sesame Snow Study Site 9,000' (2,743m)
Date New Snow Base Depth SWE Rain % Density Storm Snow Storm SWE Season Snow Season SWE Base Hi Temp Base Lo Temp Notes
10/4/2009 3.5   0.32   9 3.5 0.32 3.5 0.32      
10/5/2009 6.0   0.56   9 9.5 0.88 9.5 0.88     6.3 HS, 0.88 SWE 10/5. Daily HS based on Mammoth Pass station. SWE divided between 2 days assuming constant density.
                         
10/13/2009 Trace         Trace       36 22  
10/14/2009 21.5 21.5 4.58 1.64 21 21.5 4.58 31.0 5.46     4.58 SWE followed by 1.64 Rain. Runnels indicate heavy rain to at least 11k'. 21.5 HS was max before rain began.
                         
10/19/2009 0.0 ~4.0   0.06   0.0           Heavy rain in town would indicate greater total rainfall.
10/20/2009 2.0   0.46   23 2.0 0.46 33.0 5.92      
                         
10/27/2009 Trace         Trace           West winds in excess of 100mph at Chair 1.
10/28/2009 1.5 1.5 0.11   6 1.5 0.11 34.5 6.03     Despite cold T, SWE seems slightly low. No manual observation to verify automatic measurements. NE wind up 100mph @ 11k'
                        for several days. Starting zones presumed to be very stripped.
11/12/2009 Trace         Trace       43 27  
11/13/2009 4.0 5.0 0.48   12     38.5 6.51 28 19  
                         
11/28/2009 12.0 14.5 0.70   6 12.0 0.70 50.5 7.21 34 19 Most of the snow fell after NE wrap around.
11/29/2009 1.5 13.5 0.07   5 13.5 0.77 52.0 7.28 20 14  
                         
12/6/2009 Trace 7.0 0.03     Trace 0.03 52.0 7.31 28 12  
12/7/2009 7.0 12.5 0.69   10 7.0 0.72 59.0 8.00 15 12 Brief graupel at 7:30, ~2hrs prior to measurement.
12/8/2009 5.5 18.5 0.48   9 12.5 1.20 64.5 8.48 17 4 Strong SSW wind.
                         
12/10/2009 Trace 14.5 0.01     Trace 0.01 64.5 8.49 31 14  
12/11/2009 6.5 19.0 0.77   12 6.5 0.78 71.0 9.26 31 23 Mostly needle snow forms in AM.
12/12/2009 17.0 32.0 2.43   14 23.5 3.21 88.0 11.69 26 23  
12/13/2009 33.5 54.0 4.21   13 57.0 7.42 121.5 15.90 28 18 Graupel and some ice pellets late afternoon on 12/12. Precip gauge overwhelmed by snowfall.
12/14/2009 3.5 52.5 0.61   17 60.5 8.03 125.0 16.51 22 18 This storm almost doubled the season total snowfall and SWE. 4-6mm surface hoar on Hemlock Ridge.
                         
Date New Snow Base Depth SWE Rain % Density Storm Snow Storm SWE Season Snow Season SWE Base Hi Temp Base Lo Temp Notes
12/22/2009 9.5 49.0 1.19   12 9.5 1.19 134.5 17.70 31 15  
12/23/2009 Trace 47.5 0.01     9.5 1.20 134.5 17.71 19 5 Extremely strong NE winds. Top scoured down to rocks in some places.
                         
12/27/2009 1.0 44.0 0.11   11 1.0 0.11 135.5 17.82 40 19  
                         
12/29/2009 5.0 47.5 0.41   8 5.0 0.41 140.5 18.23 30 10  
12/30/2009 6.5 50.0 0.90   13 11.5 1.31 147.0 19.13 26 19 Widespread small avalanche activity.
12/31/2009 0.5 50.0 0.04   8 12.0 1.35 147.5 19.17 31 13  
                         
1/9/2010 1.0 42.0 0.07   7 1.0 0.07 148.5 19.24 44 31  
1/10/2010 2.0 44.0 0.24   12 3.0 0.31 150.5 19.48 44 28 2-4mm graupel on surface, ice crust on storm board.
                         
1/12/2010 Trace 43.0       Trace   150.5 19.48 43 12  
1/13/2010 15.5 58.5 2.05   13 15.5 2.05 166.0 21.53 43 23 12-16" avalanche results across most of lower mountain. Strong NE wind following storm scoured most starting zones.
                         
1/18/2010 3.0 54.5 0.35   11 3.0 0.35 169.0 21.88 29 22 6-10mm crust of melt-freeze on snow surface.
1/19/2010 25.5 73.0 2.69   11 28.5 3.04 194.5 24.57 29 18 10" new snow overnight. Many small releases PM of 1/18 on ski cuts, very few results AM of 1/19.
1/20/2010 14.0 81.0 1.08   8 42.5 4.12 208.5 25.65 29 15 Many 10-12" releases on ski cuts in AM. Hard rime ice on surface at top of Gravy Chute (~10k')
1/21/2010 20.5 92.0 1.71   8 63.0 5.83 229.0 27.36 20 5 Strong SW winds PM 1/20. 4 to 6 hour clearing in storm AM 1/21. New snowfall beginning again at 9:30.
1/22/2010 23.5 107.0 2.00   9 85.5 7.71 252.5 29.36 20 9  
1/23/2010 4.0 104.0 0.28   7 90.5 8.11 256.5 29.64 16 12 Chair 23 opens late in day.
1/24/2010 Trace 98.0 0.06     90.5 8.17 256.5 29.70 29 8 Top opens.
                         
1/25/2010 1.5 95.0 0.25   16 1.5 0.25 258.0 29.95 33 21 Very little new snow, but a great deal of wind drifting.
                         
Date New Snow Base Depth SWE Rain % Density Storm Snow Storm SWE Season Snow Season SWE Base Hi Temp Base Lo Temp Notes
1/26/2010 7.0 97.0 0.96   13 7.0 0.96 265.0 30.91 37 22 Good clearing and top opened 1/25.
                         
1/30/2010 2.5 89.0 0.16   6 2.5 0.16 267.5 31.07 37 20  
1/31/2010 1.5 88.0 0.11   7 4.0 0.27 269.0 31.18 24 9  
                         
2/5/2010 10.0 88.0 1.31   13 10.0 1.13 279.0 32.49 31 23  
2/6/2010 8.0 96.5 0.93   12 18.0 2.24 287.0 33.42 28 24  
2/7/2010 4.0 97.0 0.32   8 22.0 2.56 291.0 33.74 27 17 Moderate N wind scoured loading zones AM of 2/7.
                         
2/9/2010 Trace 93.0 0.01     Trace 0.01 291.0 33.75 32 18  
2/10/2010 5.5 97.0 0.43   8 5.5 0.44 296.5 34.18 25 11 Strong NE wind overnight scoured loading zones.
                         
2/20/2010 Trace 82.0       Trace   296.5 34.18 37 24  
2/21/2010 5.0 86.5 0.39   8 5.0 0.39 301.5 34.57 25 17  
2/22/2010 12.0 98.0 1.00   8 17.0 1.39 313.5 35.57 22 7 Strong NE wind in AM scoured upper loading zones.
                         
2/24/2010 20.5 105.5 1.88   9 20.5 1.88 334.0 37.45 33 20  
2/25/2010 9.5 112.0 1.21   13 30.0 3.09 343.5 38.66 25 22  
                         
2/27/2010 27.0 131.0 3.01   11 27.0 3.01 370.5 41.67 34 23  
2/28/2010 4.5 130.0 0.37   9 31.5 3.38 375.0 42.04 28 20 Strong NE wind scoured upper loading zones PM of 2/27.
                         
Date New Snow Base Depth SWE Rain % Density Storm Snow Storm SWE Season Snow Season SWE Base Hi Temp Base Lo Temp Notes
3/3/2010 6.0 124.0 0.77   13 6.0 0.77 381.0 42.81 31 18 Top opened for approximately one hour, moderate skier compaction.
                         
3/4/2010 13.0 134.5 1.16   9 13.0 1.16 394.0 43.97 25 11 Very heavy wind loading from SW wind.
                         
3/9/2010 5.5 125.0 0.57   10 5.5 0.57 399.5 44.54 24 2 Strong SW wind during majority of precip followed by moderate NE winds.
                         
3/10/2010 3.0 125.5 0.14   5 3.0 0.14 402.5 44.68 26 9 Strong SW wind overnight. More wind transported snow than snowfall.
                         
3/13/2010 11.0 130.5 1.53   14 11.0 1.53 413.5 46.21 34 17  
                         
3/27/2010 1.5 104.0 0.09   6 1.5 0.09 415.0 46.30 39 18 Storm preceded by two weeks of high pressure, with significant melt-freeze.
                         
3/30/2010 4.5 102.5 0.63   15 4.5 0.63 419.5 46.93 44 27  
3/31/2010 15.5 114.5 1.51   10 20.0 2.14 435.0 48.44 27 17 Very strong SW winds in excess of 120mph at Top previous day.
4/1/2010 3.0 117.5 0.26   9 23.0 2.40 438.0 48.70 20 3  
                         
4/2/2010 Trace 115.0       Trace   438.0 48.70 27 6  
4/3/2010 4.0 118.5 0.96   24 4.0 0.96 442.0 49.66 30 21 Dense wind slabs. Very little avalanche activity.
                         
4/4/2010 0.5 117.0 0.08   16 0.5 0.08 442.5 49.74 29 17  
                         
4/5/2010 25.5 135.0 3.03   12 25.5 3.03 468.0 52.77 25 16 100+ mph WSW to SW winds for several hours overnight at Top and Ch22 stations.
4/6/2010 2.0 138.5 0.23   12 27.5 3.26 470.0 53.00 20 13 Winds shifted to NW in AM of 4/6.
                         
4/12/2010 19.5 134.5 1.98   10 19.5 1.98 489.5 54.98 36 17  
4/13/2010 2.5 134.5 0.35   14 22.0 2.33 492.0 55.33 23 16  
                         
4/20/2010 Trace 112.5 0.04     Trace 0.04 492.0 55.37 51 31  
4/21/2010 7.0 123.5 0.70   10 7.0 0.74 499.0 56.07 32 15 Brief clearing AM of 4/21.
4/22/2010 2.5 123.5 0.16   6 9.5 0.90 501.5 56.23 22 14  
4/23/2010 2.0 123.5 0.17   9 11.5 1.07 503.5 56.40 28 20  
All observations are made in the morning, therefore all measurements are for new snow during approximately the previous 24 hours.
Units for Base Depth, New Snow, Storm Total, and Season Snowfall are in inches.
SWE≡Snow Water Equivalent, the amount of water produced from melting a known volume of snow, measured in inches of H2O.
Units for 24 Hour Base Hi Temp and Base Lo Temp are degrees Fahrenheit.
HS=Height of Snow
Line breaks indicate clearing between storms, despite occasional consecutive days.