Niwot Ridge LTER Snow Report for May 2006
15 May 2006 Niwot (C1) Snowpack Report

The snow water equivalent (SWE) of the snowpack at C1 was 0.875 inches on 15 May 2006. The Snotel reports 1.0” which is 12% of average, while the cumulative winter precipitation is 19.4” for 88% of average. These values would have been somewhat of a surprise six weeks ago, when SWE was 103%, but illustrate how sensitive snowpack is to changes in weather. The University Camp Snotel is an interesting contrast to the Niwot site. This site is just a few kilometers west, and nearer to the Continental Divide, than Niwot and the snowpack is 95% of average. The reason for this is at least twofold. First, this winter the westerly winds were strong, meaning greater wind-blown deposits and orographic snowfall for locations closest to the Divide. Second, U Camp is a slightly higher and colder than Niwot. The difference in these two sites is interesting not only because it illustrates the dramatic effect that just a few kilometers make as to weather anomalies a location experiences, but also because this could be similar to the signature of a rising freezing level in a warmer climate. Much attention has been given to rising freezing levels in tropical and maritime snowpacks since they are already near the zero degree Celsius (C) isotherm; a slight increase in temperature would be disastrous to their snowpacks. Since continental snowpacks, such as those in Colorado are so much colder than zero C, they can survive a significant temperature rise, or so it might seem. However, as the freezing level rises even in very cold, continental climates, snowpack meltout occurs earlier, particularly noticeable at lower elevations, and is accompanied by the associated negative consequences of reduced snowpack. Rising freezing levels have another compounding effect, even in the cold continental areas; the loss of snowpack is not a linear function of the rise in elevation, but is actually much greater. This is because there is much more surface area lower on the mountains, so the absolute quantity of SWE lost to a slight rise in temperatures is great.

Conditions in Colorado: Snowpack decreased rapidly these past two weeks in the state, as well. The South Platte now has 77% SWE and 94% cumulative winter precipitation (ppt). This is the second highest basin SWE in the state, with the Larmie/North Platte having 78% SWE and 103% ppt. The lowest are the San Juan/Miguel/Dolores/Animas with 28% SWE and 77% ppt, and the Upper Rio Grande with 28% SWE and 80% ppt.

The western US snowpack pattern continues to show the relatively unchanged La Nina pattern: healthy in the north, weak in the south. Both the California Great Basin sites and the state of Washington have high SWE and Snowpack Indices greater than one with 158% SWE and 147% ppt for CA, and 124% SWE and 99% ppt for Washington. Idaho, Nevada, and Oregon are all above average, but there is no snowpack to be reported in Arizona or New Mexico. These last two states have only received 41% and 47% of their normal winter precipitation (respectively), as well, so the southwest drought continues, with only last year as a (brief?) respite.

In conclusion, an interesting high versus low elevation snowpack situation in the Front Range has developed. The lower elevations (less than about 10,500 feet) are very dry even after having near or above normal snowpacks until last month. The higher elevations, in stark contrast, have maintained a healthy snowpack. This is fortunate for the City of Boulder, for this is where its Front Range watershed is located.

The next, and final report will come when meltout occurs at Niwot, which will be any day now. As a preview of that report, this year could be the third earliest meltout since 1981. It is already the fifth earliest occurrence of peak SWE (3 April; mean peak date is 19 April), and this peak is the tenth lowest in the past 26 years.

Sno Tel Data  Niwot Ridge, C-1
Snow Water Content (inches)
Values are for the end of given month
except as noted for May and June

    Season     Dec      Jan      Feb      Mar      Apr     May            Jun 
      81/82    4.75     10.5     11.75    15.5     14.9    12.0   (17th)
      82/83    3.63              4.75     12.75     17     11.75  (30th)
      83/84    12.6     13.25     15      18.9     20.75   
      84/85    3.75     6.25      8.5     10.25    8.75
      85/86     6.5      7.5      14      15.38    17.5
      86/87    6.25     8.75     11.25    12.75    11.75
      87/88     6.5      9.1     12.4     15.75    14.5
      88/89     5.5      7.6      11      10.25     5.6
      89/90     6.5     9.25     10.75    16.1     16.5
      90/91      3        5       7.1     9.38      10
      91/92    6.65     6.75      8.5     12.25    10.25
      92/93    5.75     6.75     10.75     14      15.875
      93/94    7.125    9.063    12.25    13.25    13.25     2.5  (18th)
      94/95    2.625    3.925     7.0     10.125   16.75    17.0  (22nd) 12.375(13th) 19.75(30th)
      95/96    7.50     12.00    17.5     20.375   18.75     6.125 (15th)
      96/97    8.75     12.625   15.125   14.625   20.375   18.0   (15th)
      97/98    7.0625   10.0     10.125   12.875   17.25    12.875 (15th)
      98/99    3.25     6.625     8.375    9.125   14.125   14.25  (15th)
      99/2000  3.5      7.5      10.625   12.375    7.625   
      00/2001  4.375    5.375     7.125   10.00     9.125
      01/2002  2.625    4.25      6.19     7.563    0.0
      02/2003  4.00     5.25      8.5     16.75    14.375   11.44 (15th)
      03/2004  2.75     4.813     7.75     7.875   10.125    3.69 (14th)
      04/2005  4.875    7.7       9.5     11.625   12.875   12.25 (15th)
      05/2006  5.625    8.375     9.5     13.25     6.75     0.875 (15th)

     Average   5.418    7.842    10.212   12.922   12.99