The Pacific/ North American Teleconnection Pattern and United States Climate. Part I: Regional Temperature and Precipitation Associations

The Pacific/ North American (PNA) teleconnection index, a measure of the strength and phase of the PNA teleconnection pattern, is related to the variations of the surface climate of the United States from 1947 through 1982 for the autumn, winter, and spring months when the PNA is a main mode of Northern Hemisphere mid-tropospheric variability. The results demonstrate that the PNA index is highly correlated with both regional temperature and precipitation. The strongest, most extensive correlations between the index and temperature are observed in winter, but large areas of the country show important associations during the spring and autumn as well. Although the centers of highest correlation migrate systematically with changes in the circumpolar vortex over the course of the annual cycle, the southeastern and northwestern parts of the United States possess consistently high index- temperature correlations. Correlations between the PNA index and precipitation are weaker and less extensive than those for temperature, but large coherent regions of high correlations are observed across the nation. Winter and early spring exhibit the strongest relationships because spatially coherent synoptic-scale systems, related to the long-wave pattern, control precipitation. The late spring and early autumn seasons have the least extensive and weakest correlations due to the importance of less organized smaller-scale convective rainfall events

Climatology of the daily temperature range annual cycle in the United States

Many researchers are presently interested in detecting long-term trends in annual or seasonal daily temperature range (DTR), and attributing these changes to anthropogenic origins. However, very little work has been done to confirm the mechanisms that are important to determining the long-term average annual cycle of the DTR. Therefore, the focus of this work is to examine the spatial and temporal difference in the DTR average annual cycle across the United States, and to associate the patterns of these cycles with potential causal variables. Three major types of DTR annual cycle exist in the United States: high sun season maximum (northern and western U.S.), low sun season maximum (south central and southeast U.S.), and transitional season maxima (middle latitude in the U.S.). The annual cycles of the DTR in the northern and western U.S. are well related to average annual cycles of cloud cover and dew point temperature; only areas to the west of the Rocky Mountains have a strong linkage between DTR and precipitation frequency annual cycles. Across the northern tier of the U.S., the loss of snow cover is important to DTR transitions during the spring season. However, the onset of snow cover in the fall does not appear to be the major factor in DTR variations, which are instead more strongly associated with cloud cover effects. As expected from their sinusoidal annual cycle, maximum and minimum temperature cycles are linearly related to the DTR in regions with a warm season or cold season DTR maximum, while non-linear relationships exist where the DTR annual cycle has maxima in the transition seasons

Trends in Twentieth-Century U.S. Snowfall Using a Quality-Controlled Dataset

A quality assessment of daily manual snowfall data has been undertaken for all U.S. long-term stations and their suitability for climate research. The assessment utilized expert judgment on the quality of each station. Through this process, the authors have identified a set of stations believed to be suitable for analysis of trends. Since the 1920s, snowfall has been declining in the West and the mid-Atlantic coast. In some places during recent years the decline has been more precipitous, strongly trending downward along the southern margins of the seasonal snow region, the southern Missouri River basin, and parts of the Northeast. Snowfall has been increasing since the 1920s in the lee of the Rocky Mountains, the Great Lakes– northern Ohio Valley, and parts of the north-central United States. These areas that are in opposition to the overall pattern of declining snowfall seem to be associated with specific dynamical processes, such as upslope snow and lake-effect snow that may be responding to changes in atmospheric circulation

Spatial distribution, variation, and trends in storm precipitation characteristics associated with soil erosion in the United States

"November 2002.""Prepared for the United States Department of Agriculture.

Trends in Twentieth-Century U.S. Snowfall Using a Quality-Controlled Dataset

A quality assessment of daily manual snowfall data has been undertaken for all U.S. long-term stations and their suitability for climate research. The assessment utilized expert judgment on the quality of each station. Through this process, the authors have identified a set of stations believed to be suitable for analysis of trends. Since the 1920s, snowfall has been declining in the West and the mid-Atlantic coast. In some places during recent years the decline has been more precipitous, strongly trending downward along the southern margins of the seasonal snow region, the southern Missouri River basin, and parts of the Northeast. Snowfall has been increasing since the 1920s in the lee of the Rocky Mountains, the Great Lakes– northern Ohio Valley, and parts of the north-central United States. These areas that are in opposition to the overall pattern of declining snowfall seem to be associated with specific dynamical processes, such as upslope snow and lake-effect snow that may be responding to changes in atmospheric circulation

Trends in Twentieth-Century U.S. Extreme Snowfall Seasons

Temporal variability in the occurrence of the most extreme snowfall years, both those with abundant snowfall amounts and those lacking snowfall, was examined using a set of 440 quality-controlled, homogenous U.S. snowfall records. The frequencies with which winter-centered annual snowfall totals exceeded the 90th and 10th percentile thresholds at individual stations were calculated from 1900–01 to 2006–07 for the conterminous United States, and for 9 standard climate regions. The area-weighted conterminous U.S. results do not show a statistically significant trend in the occurrence of either high or low snowfall years for the 107-yr period, but there are regional trends. Large decreases in the frequency of low-extreme snowfall years in the west north-central and east north-central United States are balanced by large increases in the frequency of low-extreme snowfall years in the Northeast, Southeast, and Northwest. During the latter portion of the period, from 1950–51 to 2006–07, trends are much more consistent, with the United States as a whole and the central and northwest U.S. regions in particular showing significant declines in high-extreme snowfall years, and four regions showing significant increases in the frequency of low-extreme snowfall years (i.e., Northeast, Southeast, south, and Northwest). In almost all regions of the United States, temperature during November–March is more highly correlated than precipitation to the occurrence of extreme snowfall years. El Nin ̃ o events are strongly associated with an increase in low-extreme snowfall years over the United States as a whole, and in the northwest, northeast, and central regions. A reduction in low-extreme snowfall years in the Southwest is also associated with El Nin ̃ o. The impacts of La Nin ̃ a events are strongest in the south and Southeast, favoring fewer high-extreme snowfall years, and, in the case of the south, more low-extreme snowfall years occur. The Northwest also has a significant reduction in the chance of a low-extreme snowfall year during La Nin ̃ a. A combination of trends in temperature in the United States and changes in the frequency of ENSO modes influences the frequency of extreme snowfall years in the United States

Trend Identification in Twentieth-Century U.S. Snowfall: The Challenges

There is an increasing interest in examining long-term trends in measures of snow climatology. An examination of the U.S. daily snowfall records for 1900–2004 revealed numerous apparent inconsistencies. For example, long-term snowfall trends among neighboring lake-effect stations differ greatly from insignificant to +100% century -1. Internal inconsistencies in the snow records, such as a lack of upward trends in maximum seasonal snow depth at stations with large upward trends in snowfall, point to inhomogeneities. Nationwide, the frequency of daily observations with a 10:1 snowfall-to-liquid-equivalent ratio declined from 30% in the 1930s to a current value of around 10%, a change that is clearly due to observational practice. There then must be biases in cold-season liquid-equivalent precipitation, or snowfall, or both. An empirical adjustment of snow-event, liquid-equivalent precipitation indicates that the potential biases can be statistically significant. Examples from this study show that there are nonclimatic issues that complicate the identification of and significantly change the trends in snow variables. Thus, great care should be taken in interpretation of time series of snow-related variables from the Cooperative Observer Program (COOP) network. Furthermore, full documentation of optional practices should be required of network observers so that future users of these data can properly account for such practices

The Pacific/ North American Teleconnection Pattern and United States Climate. Part I: Regional Temperature and Precipitation Associations

The Pacific/ North American (PNA) teleconnection index, a measure of the strength and phase of the PNA teleconnection pattern, is related to the variations of the surface climate of the United States from 1947 through 1982 for the autumn, winter, and spring months when the PNA is a main mode of Northern Hemisphere mid-tropospheric variability. The results demonstrate that the PNA index is highly correlated with both regional temperature and precipitation. The strongest, most extensive correlations between the index and temperature are observed in winter, but large areas of the country show important associations during the spring and autumn as well. Although the centers of highest correlation migrate systematically with changes in the circumpolar vortex over the course of the annual cycle, the southeastern and northwestern parts of the United States possess consistently high index- temperature correlations. Correlations between the PNA index and precipitation are weaker and less extensive than those for temperature, but large coherent regions of high correlations are observed across the nation. Winter and early spring exhibit the strongest relationships because spatially coherent synoptic-scale systems, related to the long-wave pattern, control precipitation. The late spring and early autumn seasons have the least extensive and weakest correlations due to the importance of less organized smaller-scale convective rainfall events

Drought Planning for Small Community Water Systems

Midwest Technology Assistance Centerpublished or submitted for publicationis peer reviewe

Climatology of the daily temperature range annual cycle in the United States

Many researchers are presently interested in detecting long-term trends in annual or seasonal daily temperature range (DTR), and attributing these changes to anthropogenic origins. However, very little work has been done to confirm the mechanisms that are important to determining the long-term average annual cycle of the DTR. Therefore, the focus of this work is to examine the spatial and temporal difference in the DTR average annual cycle across the United States, and to associate the patterns of these cycles with potential causal variables. Three major types of DTR annual cycle exist in the United States: high sun season maximum (northern and western U.S.), low sun season maximum (south central and southeast U.S.), and transitional season maxima (middle latitude in the U.S.). The annual cycles of the DTR in the northern and western U.S. are well related to average annual cycles of cloud cover and dew point temperature; only areas to the west of the Rocky Mountains have a strong linkage between DTR and precipitation frequency annual cycles. Across the northern tier of the U.S., the loss of snow cover is important to DTR transitions during the spring season. However, the onset of snow cover in the fall does not appear to be the major factor in DTR variations, which are instead more strongly associated with cloud cover effects. As expected from their sinusoidal annual cycle, maximum and minimum temperature cycles are linearly related to the DTR in regions with a warm season or cold season DTR maximum, while non-linear relationships exist where the DTR annual cycle has maxima in the transition seasons