Picture: Spill at Pathfinder Dam, North Platte RiverJune 2011

Missouri Basin Forecasters Meeting – February 20-21, 2013

Cara McCarthyNatural Resources Conservation ServiceSnow Survey and Water Supply Forecast ProgramNational Water and Climate CenterPortland, OR

Entry to Geneva Park Snow Course, South Platte, for February 1st, 2013 Measurement,60% of Normal

• Water Supply Forecasts/Current Conditions• A SNOTEL site you should not use for SWE• Snow Course Reductions• Change to 1981-2010 SWE Medians

Sawtooth Snow Course, South PlatteFeb 1st Measurement

February 1, 2013

Feb 1, 2013

February 1, 2013Snow Water Equivalent

as % of Normal (Median)

SNOTELMonth-to-Date Precipitation

% of Normal

February 18, 2013

Feb 18, 2013SWE

% Normal

Feb 1, 2013SWE

% of Normal

Change in SNOTEL Snow Water Equivalent since February 1

Month-to-Date Guidance Forecast Change as Percent of 1981-2010 Normal

Feb 18, 2013

From Lucas Zukiewicz, NRCS SSWSF Montana DCO 2/7/2013

Pike Creek SNOTEL May 2009

Pike Creek SNOTEL May 2009

Bear Basin Snow Course 2006

39 Snow Course Reductions in Montana DCO Area

New Normals this Year

• Every decade the 30 year normals change periods.• This year we go from the 1971-2000 period to the

1981-2010 period.• The change is meant to keep pace with current

climatic conditions as the most recent years are said to represent the current conditions.

• Most data types are calculated as a straight average except Snow Water Equivalent which is “median” or “middle value”

Why will SWE use a median?

Lewis Lake Divide SNOTEL Site Yellowstone NP January 16, 2013

Effect of Change to Median SWE 1981-2010

http://www.wcc.nrcs.usda.gov/reportGenerator/

Questions?

www.wcc.nrcs.usda.gov