2010 EASTERN SNOW CONFERENCE MEETING PROGRAM (original) (raw)
Related papers
A Collaborative Approach to Study Northwest Flow Snow in The Southern Appalachians
Bulletin of The American Meteorological Society, 2009
N orthwest flow snow (NWFS) in the southern Appalachian region occurs during periods of moist, upslope flow in association with northwest low-level wind, often resulting in significant snowfall in the absence of synoptic-scale upward vertical motion. Very sharp snow accumulation gradients are created by the superposition of the synoptic-scale flow across the long, but rather narrow, mountain range and smaller-scale upward and downward motions induced by the numerous ridges and valleys intersecting at various angles. Snowfall totals can range from a trace to over a meter from event to event or even within a single event. The highly variable nature of the snowfall in terms of duration, spatial distribution, and amount is such that observational and forecast techniques were not conducive to providing useful advance notice of these events until fairly recently. Frequently, forecasts of post-cold frontal weather mentioned only "snow flurries," which implied no accumulation. Indeed, flurries often occurred, but many events also included Improved understanding and forecasting of northwest flow snow is the focus of a unique team of academic and operational colleagues from several universities and National Weather Service offices.
Remote Sensing of Environment, 2015
Snow provides a key water source for stream flow and agricultural production across western North America and drinking water for large populations in the Southwest. Accurate estimates of snow cover spatial distribution and temporal dynamics are important at regional and local scales as snow cover is projected to decrease due to global climate change. We examined regional-scale temporal trends in snow distribution across central and northern Arizona using two tiles of 2928 daily images of MOD10 snow product. The analysis included the entire MODIS archive time period, October 1, 2003-June 1, 2014, and a 245,041 km 2 area of 51 HUC8 watersheds. We also examined the effects of a regional forest restoration effort, known as the Four Forest Restoration Initiative (4FRI), aimed at enhancing snow accumulation and retention for increased groundwater recharge through forest thinning and burning treatments. We analyzed 66 Landsat TM/ETM + images spanning 26 years between 1988 and 2014 at five sites and one hyperspectral image from 2014 at two sites. The MOD10 snow product performs well in estimating Arizona's thin and discontinuous snow distribution. Mann-Kendall time-series analysis indicate significantly increasing trends in the annual number of snow cover days (SCD) over the 12-year period in 1.6% of the region at elevation transitions such as the Mogollon Rim in central Arizona, while significantly decreasing trends are observed at a few locations of lower elevations leading to the desert margins in eastern Arizona. The observed temporal trends are mostly consistent with ground-based SNOTEL snow measurements. An Arizona specific, Landsat sensor-derived binary classification model, similar to the MOD10 product, was developed at a local scale. It performs better than commonly-used simple threshold-based approaches, but demonstrates the continued challenges associated with Landsat sensor-derived snow classification in Arizona likely due to its coarse temporal resolution. Landsat-derived multi-temporal Normalized Difference Snow Index (NDSI) analysis indicate that treated (thinned and thinned-and-burned) forest sites had significantly greater NDSI values than untreated control sites. Snowpack at treated sites also appeared to persist longer into the spring season with potentially greater contributions to groundwater recharge in this semi-arid region. The high-resolution hyperspectral data analysis indicate that sites treated to approximately 24% forest canopy cover appear to have an optimum threshold for accumulating and maintaining snowpack. It balances canopy cover versus canopy gap, which reduces snow interception and sublimation by canopy, while providing enough shade. These results are encouraging for the 4FRI, the first and largest forest restoration effort in the US history, aimed at improving watershed health and function in the face of changing climate.
The hydrological sensitivity of snowmelt-dominated, high mountain headwaters to climate change was investigated using a physically based model to diagnose snow processes and headwater basin runoff response to perturbations of the current climate in three well-instrumented mountain research basins spanning the northern North American Cordillera. High-resolution hourly meteorological observations were perturbed using air temperature increases and precipitation changes and then used to force comprehensive, mountain hydrological models created using the modular, process-based Cold Regions Hydrological Modelling Platform (CRHM) for each basin. Simulations using multiple elevations show that both peak snowpack and annual runoff respond to warming and precipitation changes and these responses vary with latitude. In all three basins, the timing and magnitude of peak snowpack were sensitive to changes in temperature and precipitation, but timing was most sensitive to temperature. Annual runoff was far less sensitive to temperature than the snow regime. The impacts of the range of warming expected from North American climate model simulations on annual runoff, but not peak snowpack, can be offset by the size of precipitation increases projected for the future period 2041-2070. To offset the impact of 2°C warming on annual runoff, precipitation would need to increase by less than 5% in all three basins. To offset the impact of 2°C warming on peak snowpack, however, precipitation would need to increase by 12% in Wolf Creek-Yukon Territory, 18% in Marmot Creek-Canadian Rockies and an amount greater than the maximum projected at Reynolds Mountain-Idaho. The role of increased precipitation as a compensator for the impact of warming on mountain snow hydrology is more effective at the high elevations and high latitudes. Increased precipitation leads to resilient and strongly coupled snow and hydrological regimes in cold regions and sensitive and weakly coupled regimes in the low elevations and temperate climate zones.
Now You See It Now You Don’t: A Case Study of Ephemeral Snowpacks in the Great Basin U.S.A
Ephemeral snowpacks, or those that routinely experience accumulation and ablation at the same time and persist for <60 days, are challenging to observe and model. Using 328 site years from the Great Basin, we show that ephemeral snowmelt delivers water earlier than seasonal snowmelt. For example, we found that day of peak soil moisture preceded day of last snowmelt in the Great Basin by 79 days for shallow soil moisture in ephemeral snowmelt compared to 5 days for seasonal snowmelt. To understand Great Basin snow distribution, we used moderate resolution imaging spectroradiometer (MODIS) and Snow Data Assimilation System (SNODAS) data from water years 2005-2014 to map snow extent. During this time period snowpack was highly variable. The maximum seasonal snow cover was 64 % in 2010 and the minimum was 24 % in 2014. We found that elevation had a strong control on snow ephemerality, and nearly all snowpacks over 2500 m were seasonal. Snowpacks were more likely to be ephemeral on south facing slopes than north facing slopes at elevations above 2500 m. Additionally, we used SNODAS-derived estimates of solid and liquid precipitation, melt, sublimation, and blowing snow sublimation to define snow ephemerality mechanisms. In warm years, the Great Basin shifts to ephemerally dominant as the rain-snow transition increases in elevation. Given that snow ephemerality is expected to increase as a consequence of climate change, we put forward several challenges and recommendations to bolster physics based modeling of ephemeral snow such as better metrics for snow ephemerality and more ground-based observations.
Journal of Climate, 2016
The potential effects of climate change on the snowpack of the northeastern and upper Midwest United States are assessed using statistically downscaled climate projections from an ensemble of 10 climate models and a macroscale hydrological model. Climate simulations for the region indicate warmer-than-normal temperatures and wetter conditions for the snow season (November–April) during the twenty-first century. However, despite projected increases in seasonal precipitation, statistically significant negative trends in snow water equivalent (SWE) are found for the region. Snow cover is likely to migrate northward in the future as a result of warmer-than-present air temperatures, with higher loss rates in northern latitudes and at high elevation. Decreases in future (2041–95) snow cover in early spring will likely affect the timing of maximum spring peak streamflow, with earlier peaks predicted in more than 80% of the 124 basins studied.
2008
Snow hydrology is a specialized field of hydrology that is of particular importance for high latitudes and mountainous terrain. In many parts of the world, river and groundwater supplies for domestic, irrigation, industrial, and ecosystem needs are generated from snowmelt, and an in-depth understanding of snow hydrology is of clear importance. Study of the impacts of global warming has also stimulated interest in snow hydrology because increased air temperatures are projected to have major impacts on the snow hydrology of cold regions.
Journal of Geophysical Research, 2007
1] Snow cover strongly interacts with climate through snow albedo feedbacks. However, global climate models still are not adequate in representing snow cover fraction (SCF), i.e., the fraction of a model grid cell covered by snow. Through an analysis of the advanced very high resolution radiometer (AVHRR) derived SCF and the Canadian Meteorological Centre (CMC) gridded snow depth and snow water equivalent (SWE), we found that the SCF-snow depth relationship varies with seasons, which may be approximated by variations in snow density. We then added snow density to an existing SCF formulation to reflect the variations in the SCF-snow depth relationship with seasons. The reconstructed SCF with the gridded snow depth and SWE by employing this snow density-dependent SCF formulation agrees better with the AVHRR-derived SCF than other formulations. The default SCF formulation in the National Center for Atmospheric Research community land model (CLM), driven by observed near-surface meteorological forcings, simulates a smaller SCF and a shallower snow depth than observations. Implementation of the new SCF formulation into the NCAR CLM greatly improves the simulations of SCF, snow depth, and SWE in most North American (NA) river basins. The new SCF formulation increases SCF by 20-40%, decreases net solar radiation by up to 20 W m À2 , and decreases surface temperature by up to 4 K in most midlatitude regions in winter and at high latitudes in spring. The new scheme reproduces the observed SCF, snow depth, and SWE in terms of interannual variability and interbasin variability in most NA river basins except for the mountainous Columbia and Colorado River basins. It produces SCF trends similar to that of AVHRR. However, it produces greater decreasing trends in ablation seasons and smaller increasing trends in accumulation seasons than those of the CMC snow depth and SWE.