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Flattop Mountain SNOTEL Snowpack: Water Year 2004

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These materials prepared by the Climate Change in Mountain Ecosystems Program -- U.S. Geological Survey, Glacier Field Station.  Dan Fagre, Program Coordinator, email: dan_fagre@usgs.gov.  For more information, visit the Glacier Field Station - Climate Change in Mountain Ecosystems program (CCME) web site. 


Snow Pillow

The Flattop Mountain SNOTEL (SNOw TELemetry) station is one of nearly 600 similar stations operated throughout the western United States by the Natural Resources Conservations Service (NRCS, U.S. Department of Agriculture). These stations measure and record Snow Water Equivalent (SWE), which is the weight of snow water equivalent to inches of water. Most SNOTEL sites also measure temperature and precipitation; many now measure snow depth as well. Various agencies and organizations use the data from the stations to forecast water availability, floods, and avalanche hazard. 

The Flattop Mountain SNOTEL station has operated since October 1st, 1969. To help calculate water storage and availability during agricultural growing seasons, the data are compiled by water year; a water year runs from 1 October - 30 September. SWE records from the station extend for 33 water years (1970-2002). Precipitation records from the station start water year 1979, with temperature records starting water year 1983.

SnowTel siteThe Flattop Mountain SNOTEL station is located at approximately 6300 feet in elevation on Flattop Mountain, a high plateau between the Lewis and Livingston Ranges in Glacier National Park, Montana. The site is three air miles south of the Continental Divide. During the winter, complex combinations of weather and terrain determine snowfall at the site. Westerly weather systems dominate, bringing moisture from the Gulf of Alaska or Pacific Ocean. Less frequent northerly systems spill drier Arctic air through passes on the Continental Divide as they slide south along the Rocky Mountain Front. Flattop Mountain's position between the Livingston and Lewis Ranges amplifies the effects of these large-scale weather systems; the two ranges rise 2-4000 feet above the site and orographically wring moisture from both westerly and upslope easterly storms. Flattop Mountain is a useful indicator of snowfall throughout Glacier National Park because it is subject to the factors that influence conditions elsewhere in the park.

The graph below shows the current water year SWE at Flattop Mountain along with snow depth and average daily temp:

SWE, snow depth and temperature at Flattop Mountain

A .PDF version of this graph is available at SWE, depth and temperature.

Since the last update of this webpage (May 10th), the snowpack at Flattop Mtn. SNOTEL station continued its annual melt. Conditions in May and early June have generally been wet, with average temperatures. The station recorded .1” or more of precipitation on 27 of 44 days, for a total of 8.3” of precipitation, 5.2” of that during May. Nearly all of that fell as rain; the station has measured just 1” of
SWE gain in May and .5” in June. The highest one-day rainfall was .9” on May 28th, while the longest stretch of days with precipitation
was May 25th – May 30th. It was followed by the longest period without precipitation, May 31st – June 4th. The precipitation of the past four weeks is common for this time of year; the station typically shows a secondary peak in precipitation known locally as the “June Monsoon.”

The station recorded the warmest temperatures early in the month. After a mid-month winter storm, temperatures remained cool. Maximum and minimum temperatures for May were 16.7 C (60 F) on May 1st and -8 C (17.6 F) on May 12th. The highest mean daily temperature for the month was 8.2 C (47.8 F) on May 7th. The mean monthly temperature was 3.7 C (38.6 F), which is identical to the mean monthly temperature for May for the 21 years (1982-2003) that the station has recorded temperatures.

The average temperatures for the month ended a trend of above-average temperatures that dominated the winter. November has so far been the only month of the 2004 Water Year with mean temperatures below average. From December through April, mean monthly temperatures have remained above average, with December and January warmer than the mean (2.6 C/4.7 F and .5 C/1 F respectively), and February and March substantially warmer than average (3.2 C/ 5.8 F for February; 5 C/ 9 F for March). The difference between 2004 and the 21-year average narrowed in April and closed in May. The Mean Monthly Temperature Comparison Graph below shows this pattern. While the graph shows a relatively normal curve to the temperatures, the curve appears shifted a month forward. That is, early winter temperatures are typical mid-winter temperature, and late winter/ early spring temperatures are typical of late spring. A .pdf version of this graph is available at Mean Monthly Temperature Graph.

The warm temperatures of the winter had a significant effect on the snowpack at the station. Despite a dry February, SWE gain f for February-April was 15.9”, which is average. The warm temperatures, however, have resulted in 7” of SWE loss in the same period, leaving the snowpack considerably below average when it peaked on April 20th, a week earlier than the 34-year average of April 27th. The SWE total was 37.4”, or 81% of the 34-year average of 46.74”. In addition to the 7” of SWE loss in March and April, the station lost 1.2” of SWE in October, for a total loss of 8.2” – nearly enough to make up the 9.3 inch deficit on April 20th. It’s thus reasonable to conclude that the below average snowpack at Flattop Mtn. SNOTEL is primarily the result of warm temperatures rather than lack of precipitation. A graph showing the monthly SWE gain at Flattop Mountain SNOTEL is below; a .pdf version of the graph can be found at Monthly SWE 2004.

Since April 30th, the snow pillow at Flattop has recorded 22” of SWE loss and 1.5” of SWE gain. The station measured 13” of SWE loss and 1” of SWE gain in May. The greatest SWE loss occurred May 18th (1.1”) and June 3rd (1.4”). As of midnight, June 14th, the SWE total at Flattop was 16.7”, which represents 74% of the 34-year average of 25.3”. Snow depth was 33”. Despite the below-average SWE total, conditions at the station are well within the range of the past 34 water years. The maximum SWE are recorded on this day (Julian Day 165) was 48.6” in 1974; the minimum was 0” in 1987, a 48.6” range. All told, there have been 12 years in the 34-year history of the station in which SWE total on this date was lower. The SWE total on this date last year was 22.6”, with a snow depth of 44.5”. A graph comparing SWE for significant water years is below.

SWE at Flattop Mountain

A more detailed .PDF version of this graph is available for printing or viewing at SWE Comparison Graph.

In its June10th El Nino/ENSO Discussion, the National Weather Service Climate Prediction Center (CPC) reported that oceanic and atmospheric conditions In May throughout the Pacific Basin were typical of neutral phase of the El Nino Oscillation. The CPC reported that Sea Surface Temperature (SST) anomalies have been warmer than average in the western and central equatorial Pacific and cooler than average in the eastern equatorial Pacific. These anomalies have led to precipitation and wind speed gradients across the equatorial Pacific, with precipitation and wind speeds generally higher in the western portion of the equatorial Pacific. Forecasts of conditions for the next 3 months are split, with some models predicting neutral conditions and others El Nino conditions. The CPC concluded that ENSO-neutral conditions are more likely through August 2004, while noting that trends after that are uncertain.

For more information, see the climate prediction center's El Nino/ENSO Discussion.