15 May 2005 Greetings!

The snowpack at Niwot continues to be quite healthy at this late date. 
On 15 May 2005, the manual measurement of the Niwot snowpack shows 12.25" SWE 
(no percentage rating available, but the historic record follows this message), 
a depth of 31.6", and density of 39%.  This SWE is greater than at the end of any 
month in the last (2003-04) season, and the highest 15 May SWE since 1999.
It peaked on 4 May  with 13.4" of snow water equivalent (SWE), 119% of average for 
that date (Snotel data).  This is much later than the average peak date of April 18.  
Thus, there may be a later start of the fire season, and perhaps healthy stream flows 
longer into the summer, depending on summer rains. 
It is worth noting that we enter this spring runoff season in a semi-unique, and 
favorable, condition.  Normally, soil conditions are fairly dry in the fall leaving 
the next spring runoff to fill the deficit before filling streams and rivers.  But this 
season, fall soil moisture was near field capacity, leaving more water available for 
stream flow, because there is no soil moisture deficit to replace.

The Snotel records shows Niwot at 146% of average (total winter precipitation is 103%), 
and the South Platte snowpack is104% of average (89% for total winter precipitation).  
The high percentages are less reflective of how much water we actually have compared to 
the total cumulative winter precipitation figures, because it is so late in the season.  
The SWE percentages are really telling how much later than average the snowpack is 
melting out.  For example, Niwot SWE was 13.4" and 119% of average on May 4, compared to 
11.7" and 146% of average on May 15 (Snotel data).  In other words, the snowpack is not 
melting out as fast as it usually does this time of year.

The Upper Rio Grande continues to dominate the state with the highest snowpack values, 
175% and 131%, SWE and winter precipitation, respectively.  The only Colorado basin that 
is doing poorly is the Yampa/White with 85% and 93% (SWE, winter precipitation, respectively).  

As has been the case all winter, the Colorado snowpack distribution reflects that of the 
western US; wet in the southwest, and drying to the north, and particularly to the northwest.  
Washington SWE is 12% of average (winter precipitation is 70%).
Utah, Nevada, and the Great Basin sites of California are all above 180%, but their cumulative 
winter  precipitation numbers are between 138% and 104%.  (Arizona and New Mexico have melted 
too much to still be reporting.)

The next and last report will be at melt-out for Niwot.  
Although the recent years have all melted out earlier than average, there is no long-term 
statistical trend.  This year may finally be latter than average, but that remains to be seen, 
as the average Niwot melt-out date is 29 May.
Melt-out date is an interesting statistic because it speaks to the question of whether the 
climate affecting our snowpack is truly changing (although it is not the only indicator).  
If there is no statistically significant trend in melt-out date, then it is just weather, 
but if there are enough years to support a statistically significant trend, then it 
may be climate change.

So, the horse race is on; will Niwot melt out before 29 May this year or not?
Until then,  

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

     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)

     Average   5.409    7.819    10.242   12.908   13.25