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Winter is ending and the growing or “frost free” season is almost here! The frost free season is defined as the continuous period of the year when the temperature does not drop below freezing. When this season starts and how long it lasts have important implications for the plants and animals that live around us, [...]

Better understanding how fluctuations in climate have affected regional wildfire frequency over the past few centuries may help to improve our ability to predict severe wildfire seasons. Some of the West’s older groves have experienced dozens of wildfires over the past few centuries. The trees that survived these fires recorded black scars in their annual [...]

Snow is both a product of the weather and a weather maker. It has long been recognized that snow exhibits a cooling effect on local and regional scales. Snow reflects more sunlight than bare ground, meaning that it absorbs less energy. More snow cover also means soils stay moist for longer following the spring melting [...]

The amount of solar energy Earth receives varies according to the “11-year solar cycle,” which corresponds to a cycle in the frequency and distribution of sunspots on the sun’s surface. The difference in solar energy between high and low points of the solar cycle is about two watts per square meter. About 35 percent of [...]

Air temperatures are fickle – they fluctuate significantly from day to day, from season to season and from year to year. The temperature of a water body fluctuates as well, but is much more constant than the surrounding air temperature. Water has a higher heat capacity than air, which means it takes far more energy [...]

Temperature records suggest that the Earth’s surface temperatures warmed during the early part of the 20th century, cooled from the period 1940-1970 and have since been warming. While Arctic temperature trends have corresponded to this general warming and cooling pattern, it has followed these trends more severely. During the warming period from 1910-1940, the Arctic [...]

Near the center of Antarctica in the polar vortex, strong westerly winds that blow in a circle around the continent during winter trap an envelope of air near the South Pole, prohibiting this air from mixing with warmer air masses closer to the equator. The extreme cold in the vortex causes clouds to form in [...]

December is East Coast Winter Storm (ECWS) season. These storms are powered by warm water that flows from the Gulf Stream. The Gulf Stream current flows along the Eastern Seaboard past Florida and the Carolinas before reaching Cape Hatteras, where the warm water heads out into the Atlantic. ECWS’s travel northward along the coast causing [...]

Winter storm season is here. Storms will be blowing in from the Pacific, bringing rainfall to lower elevations and snow to the mountains. This year, the eastern tropical Pacific is in an El Niño phase, meaning that its waters are warmer than average. When the eastern Pacific is in an El Niño phase, the northwestern [...]

Winter storm season is here. Storms will be blowing in from the Pacific, bringing rainfall to lower elevations and snow to the mountains. This year, the eastern tropical Pacific is in an El Niño phase, meaning that its waters are warmer than average. When the eastern Pacific is in an El Niño phase, the southern [...]

Winter storm season is here. Storms will be blowing in from the Pacific, bringing rainfall to lower elevations and snow to the mountains. This year, the eastern tropical Pacific is in an El Niño phase, meaning that its waters are warmer than normal. When the eastern Pacific is in an El Niño phase, the southwest [...]

It has long been known that what happens in the tropical Pacific doesn’t just stay in the tropical Pacific. Much of the year-to-year variability in America’s weather, particularly winter weather, can be explained by conditions there. All other things being equal, warm El Niño conditions off the coast of equatorial South America mean a wetter [...]

Better drought prediction systems could potentially save billions of dollars. Current prediction systems largely rely on observations of the circumstances surrounding past droughts to understand the factors that led to drying. New research reveals that: Drought in the southern Great Plains states, such as the 1946-1956 drought, can be largely explained by persistently cool conditions [...]

Global sea level is rising at a rate of about 1.2 inches per decade due to an influx of glacial melt water and thermal expansion of the oceans. The relative sea level rise that each coastal location experiences, however, differs from this global average due to local factors such as land subsidence and land uplift [...]

Variations in the temperature distribution gradient in the tropical Pacific (characterized by the state of the El Niño-Southern Oscillation (ENSO), the oscillation in the eastern tropical Pacific between cool (La Niña) and warm (El Niño) states) exerts a strong influence on upper-atmospheric circulation and affects weather throughout the world. Surface temperature distributions in the tropical [...]

The torrential rainfall and storm surges associated with hurricane landfall events can cause what are known as “overwash deposits” that leave definitive marks in the sediment layers that accumulate in coastal areas. Analyses of sediment cores from various locations along the Eastern Seaboard and Puerto Rico show that for the last 1500 years, Atlantic Hurricanes [...]

Most of the West’s water ultimately comes from ice (snowpack/glaciers) and changes in this ice can have stark impacts on streamflow. For example, in North Cascades National Park, where there is now 40 percent less glacial mass than there was in 1850, Lewis Glacier disappeared in 1990. Streamflow in the watershed it fed subsequently declined [...]

The El Niño Southern Oscillation (ENSO), the sloshing back and forth of warm water between the eastern and western tropical Pacific, influences circulation in the upper atmosphere. These circulation changes influence the behavior of the jet stream, which in turn affects regional temperature and precipitation distributions in the United States. These effects are most pronounced [...]

Some of the major uncertainties in understanding climate involve the feedbacks between surface processes and clouds. Two major shifts in northeast Pacific sea surface temperatures (SSTs) have been linked to shifts in cloud properties over the region. The first major shift occurred during 1976-77, when changes in ocean circulation caused warming of the northeast Pacific. [...]

Over an 11-year period, the intensity of the solar radiation reaching Earth varies by about 0.1 percent, which is associated with a 0.1 Kelvin (K) variance in tropospheric temperature. Changes in solar irradiance also cause fluctuations in the amount of galactic cosmic rays (high-energy subatomic particles from outside the solar system) reaching the Earth’s surface. [...]