December 30, 2005 Niwot (C1) Snowpack Report

The first report of measured snowpack from C1 brings good news.  Today, hand measurements 
showed 5.625” of snow water equivalent (SWE), or 104% of the average since December 1981.  
The Snotel reports 5.7” SWE for 110% of their average, so the 24.75” of snow on the 
ground here is above average by either measure.  This is the highest December SWE since 1997.
Although there have not been numerous large snowfalls, there has been a rather consistent 
strong zonal airflow pattern over the Continental Divide, which bring semi-continuous, but 
light, snowfall to the Colorado high country, via orographic uplift.  The Front Range snowpack 
development benefits from such a pattern, even if Boulder and Denver do not (the air warms 
enough on its decent to keep the potential snow in vapor form-the air “dries out”). 

According to Klaus Wolter, the ENSO has shifted to a weak La Nina phase.  (For more detailed 
information, his interesting executive summary can be found at 
http://www.cdc.noaa.gov/people/klaus.wolter/SWcasts/index.html#execsum)).  A La Nina condition 
is consistent with the pattern of snow delivery to the Front Range (strong zonal flow bringing 
orographic snow most of the time vs. individual, infrequent large storms of meridional flow 
origin).  It is also consistent with the snowpack distribution in Colorado and the western US, 
as the classic La Nina snowpack pattern is for Colorado and the west as a whole  to receive 
above average snowpack in the north and below average in the south.  So, the only inconsistencies 
with such a pattern right now are in Washington and the northern parts of Oregon, Idaho, and 
Montana which are below average.  This could easily change within the week, however.

Although snowpacks are looking very healthy north of approximately the 40th parallel, the 
Snowpack Index (SI) is not.  Virtually everywhere, it is less than one, meaning that 
compared to average, less of the precipitation that is falling, is not being sequestered 
in the snowpack for spring runoff.

According to the Snotel network, our South Platte basin SWE is129%, and the winter precipitation 
to date is 135%, of average.  Although all basins in northern Colorado are above average, the 
Upper Colorado River basin is the highest with 135% (144%) of average SWE (winter precipitation 
to date).  Corresponding values for the lowest basin, the Upper Rio Grande are 31% (62%), and 
Wolf Creek Summit is 29% (59%).
In the western US, Arizona’s snowpack is the lowest at 13% (31%), but New Mexico is little 
better with 18% (50%).  The Great Basin sites of California are the highest with 107% (134%).
Of the major river basins, the Missouri River Basin shows 105% (113%) of average for the highest 
honors, and the Rio Grande Basin is lowest with 25% (57%), although the lower Colorado River 
Basin is only 15% (36%).  [The Colorado River Basin as a whole is 91% (97%)].
So, is the drought over?  Well, last year the southern portion of the US was wet, this year it 
is shaping up to be the reverse, but the only state with above average reservoir storage right 
now is Arizona with 63% of capacity (average is 50%).  Every other state is below, ranging from 
4% to 15% below average.
It is still very early in this year’s snowpack season, so it will be interesting to see how 
the weather patterns develop.  If present trends continue, Arizona’s reservoirs may decrease, 
and Lake Powell may not gain at all.  

Until next month, Cheers!
Mark

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

                     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 

     Average   5.418    7.819    10.242   12.908   13.25