Although it is not warm everywhere in the Northern Hemisphere right now – Europe is shivering from a remarkably intense cold snap that has even iced over the canals of Venice – the 2011/2012 winter in North America and the United States has been unusually warm to this date in early February. Data from the North American Land Data Assimilation System Phase 2 (NLDAS-2), available at the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) indicates the unusual characteristics of this winter season.
A comparison of monthly average surface temperatures from the NLDAS Phase-2 Mosaic model (Figures 1 and 2) shows January 2012 temperatures were more than 5 degrees higher than those in January 2011 in many regions of the U.S. (Figures 3 and 4). Click on the figures to view them at full size.
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Figure 1. January 2012 monthly-averaged Surface Skin Temperature (NLDAS-2 Mosaic). Temperature scale in Kelvin.
Figure 2. January 2011 monthly-averaged Surface Skin Temperature (NLDAS-2 Mosaic). Temperature scale in Kelvin.
Figure 3. January monthly-averaged Surface Skin Temperature differences (NLDAS-2 Mosaic) between 2012 and 2011. For most of the middle and eastern U.S. regions, 2012 January average temperatures were 3 ~ 5 degrees C higher than 2011 January average temperatures, with temperature differences greater than 5 degrees C for South Dakota, Nebraska, Iowa, Mississippi, Alabama, and Georgia.
Figure 4. Time series of hourly Surface Skin Temperature (NLDAS-2 Mosaic), averaged over 125W ~ 67W, 25N ~ 49N, for 2012 winter (black line) and 2011 winter (green line). January 2012 daily high temperatures were much higher than in January 2011.
This year, most areas of the U.S have little or no snow (Figure 5), with only a few areas exceeding a low 25% threshold of snow cover. Contrast these conditions to January 2011, when the NLDAS-2 Mosaic model showed more than 60 percent of the country was covered in snow (Figure 6). Figures 7 and 8 are 2011/2012 time series comparisons of Snow Cover and Accumulated Snow Water-equivalent, respectively, showing much higher values of both variables in 2011 compared to 2012.
As the calendar moves further into February, many people may be wondering, "Where is the snow?" and "Will we have heavy snow this winter at all?" Remember last year's Groundhog Day Blizzard (Figures 9 and 10), the first billion-dollar disaster of 2011? After this storm, much of the U.S. was covered with snow, with high percentages (>80%) in the central-northern region. Also, the "Storm of the Century" in 1993 occurred March 12-14.
Even in a generally warming global climate, cold snaps and blizzards can still occur if the proper conditions are present.
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|Figure 9. Snow Cover map (daily-averaged) for the 2011 Groundhog Day blizzard (February 2, 2011) from the NLDAS-2 Mosaic model. ||Figure 10. NLDAS-2 Mosaic model Accumulated Snow Water-equivalent (daily-averaged) for the 2011 Groundhog Day blizzard (February 2, 2011). |
The North American Land Data Assimilation System Phase 2 (NLDAS-2) data set, with high spatial and temporal resolutions (0.125 x 0.125 degree, hourly) and various snow-related variables, is an excellent data source for supporting water and energy cycle investigations and case studies of winter weather events. NLDAS combines the best available observations and analyses to drive land-surface models, producing outputs of fluxes, soil moisture, soil temperature, runoff, and snow. Currently, data from the Mosaic model are available at the GES DISC. In the future, data from other models (Noah, SAC, and VIC) will also be available to the public. NLDAS-2 Mosaic snow-related variables include the following:
- Snowfall (frozen precipitation)
- Snow cover
- Snow depth
- Snow melt
- Snow phase-change heat flux
- Accumulated snow water-equivalent
- Sublimation (evaporation from snow)
- Average surface skin temperature
To further facilitate access and use of the data, NLDAS data have been made available via the Giovanni NLDAS hourly portal
. The Giovanni portal provides a simple and intuitive way to visualize, analyze, and inter-compare NLDAS data without having to download the data.
NLDAS is a collaboration effort of NOAA, NASA, Princeton University, the University of Washington, and others.
The GES DISC is a NASA earth science data center, part of the NASA Earth Science Data and Information System (ESDIS) Project.
Text and graphics provided by Hualan Rui, NASA GES DISC/Adnet Inc., following a suggestion by David Mocko, NASA GSFC Laboratory for Atmospheres/SAIC. Please contact the GES DISC Help Desk with inquiries about this article.