Articles

PROCEDURE FOR ASSIGNING A VALUE FOR TRACE PRECIPITATION DATA WITHOUT CHANGING THE CLIMATIC HISTORY

by: Adnan Akyüz, Karsten Shein, Mike Asmus

Volume 2013, No.1, 31 May 2013

Trace is the amount of precipitation that is less than 0.005” (AMS, 1959). Generally, it is not a measurable amount but just enough to wet the rain gauge that it is observed in. It is a global practice that “T” (indicating “Trace”) is entered in daily precipitation records such as the National Weather Service form B-91 under the precipitation column. Although trace is not a quantitative value, it is valuable information to better assess the weather condition of the day. However, when the precipitation data are tabulated, most spreadsheet programs do not know how to deal with a character that is not a numerical value. We explain a procedure for including trace observations when evaluating precipitation behavior over a period of time or between multiple time periods. This procedure temporarily assigns a computationally insignificant value to trace observations in order to incorporate those observations into database calculations (e.g. number of precipitation days) as well as also greatly reduce the chance of ties in the precipitation rankings. Our procedure allowed us to separate individual precipitation events in perspective especially in ranking tables without changing accumulated monthly, seasonal or annual precipitation values, thus preserving the climate history of the location.

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Extension Agent Awareness of Climate and New Directions for Research in North Carolina

by: Norman Breuer, Heather Dinon, Ryan Boyles, Gail Wilkerson

Volume 2012, No. 2, 6 Mar 2012

Each state in the United States of America has an institution known as the Cooperative Extension Service. These institutions, almost always associated with the Land Grant University’s tripartite mission of research, education, and extension, are in essence providers of adult education. In the case of climate science, they have been called a boundary organization which serves as a two-way intermediary between climate researchers and end-users. In order to better collaborate with the Extension Service, this investigation explored their attitudes toward, knowledge of, and willingness to use climate information and seasonal climate forecasts. A survey instrument was developed and distributed to North Carolina extension personnel in March 2009. A total of 109 responses were retrieved and analyzed. A principal finding is that extension agents need and desire to gain a better understanding of climate science and its application to agricultural practices. The respondents find seasonal climate forecasts to be useful and understand the economic value of forecast guidance. However, requested accuracy of seasonal climate forecasts is beyond the skill of current climate models. The survey results are discussed as well as their implication for future work in climate assessment programs regarding information to reduce risk in agriculture and natural resource management. In general, extension will continue to be a valued partner for the dissemination of climate tools and products by serving as an intermediary between climate scientists and end-users. This feedback loop can tailor and improve formats, content, presentation, access, and credibility of climate risk reduction decision support systems.

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WASHINGTON D.C. AREA 2009-2010 “SNOWMAGEDDON” WINTER SNOWFALLS BURY HISTORICAL RECORDS

by: Robert J. Leffler

Volume 2012, No. 1, 6 Mar 2012

The winter of 2009-2010 in the Washington D.C. area will likely be remembered by many arearesidents as the snowiest in their lifetimes. A rare combination of a weak-to-moderate El Nino (wet) anda very persistent negative North Atlantic Oscillation (NAO) (cold) brought a potent combination of sub-tropical moisture and cold air together over the mid-Atlantic states including the nation’s capital, resulting in an unprecedented number of major snowstorms and totalsnowfall. The extreme winter snowfalls during the most intense periods of the winter earned the winter the nickname “Snowmageddon”.

The largest snowfallsoccurred to the north of the Capital and west and northwest of Baltimore in north-central Maryland. An analysis of historical snowfall reports for the Washington D.C. metropolitan area suggests Snowmageddon’s snowfalls were unprecedented in number and amount since historical reports are available beginning in early colonial times in the early 1600’s.

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CONTINENTAL WIND PATTERNS ASSOCIATED WITH COLORADO ALPINE DUST DEPOSITION: AN APPLICATION OF THE BLM/USFS RAWS NETWORK

by: Morgan Phillips, Nolan Doesken

Volume 2011, No. 2, 21 Jun 2011

The winter and early spring of 2008-2009 brought an unusually high number of alpine dust deposition events to the Rocky Mountains of Colorado. The greatest dust accumulations were observed in the San Juan Mountains of southwestern Colorado. Significant dust accumulation was even observed along the Continental Divide in northern Colorado. The primary source for this dust has previously been identified as the Colorado Plateau. Analysis using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) atmospheric trajectory model along with satellite imagery showed that dust from the 2009 events also originated from the Colorado Plateau, especially from areas in and around northeastern Arizona that were experiencing abnormally dry conditions that spring.

The study utilized data from the BLM/USFS Remote Automated Weather Station (RAWS) network in the southwestern U.S. to identify periods of high winds corresponding to documented Colorado dust events.The RAWS database, once considered to be brief and unsuitable as a climate resource, is quickly approaching 30 years of record and provides a valuable resource for application to various climate questions. Analysis of wind data from these RAWS sites during known dust events show that a minimum threshold wind velocity exists before dust storm generation occurs, and that this threshold velocity occurs from a southwesterly direction. Threshold velocity for the daily mean speed was found to be 15 mph and 44 mph for daily maximum gusts. Wind speeds for the study region were then evaluated for the period January through April for the past 20 years in an attempt to quantify and compare both mean daily wind speed and maximum daily wind gusts on a seasonal basis. A linear regression analysis showed correlation between the Southern Oscillation Index (SOI) and the frequency of these types of high wind periods in the RAWS database, particularly during winter months. This correlation was determined to be 0.46 for daily mean wind speeds and 0.56 for maximum daily wind gusts during the months of December through April. The correlation between periods of high winds and the SOI extends through the 20 years of wind data available for these weather stations.

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THE TRANSITION OF THE BLANEY-CRIDDLE FORMULA TO THE PENMAN-MONTEITH EQUATION IN THE WESTERN UNITED STATES

by: Theodore W. Sammis, Junming Wang, David R. Miller

Volume 2011, No. 1, 21 Feb 2011

This paper reviews the history of calculating “consumptive water use,” later termed evapotranspiration (Et), for plants in the western U.S. The Blaney-Criddle formula for monthly and seasonal consumptive water use was first developed for New Mexico in 1942 for limited crops. The formula was based on the input of monthly mean air temperature and an empirical monthly/seasonal coefficient. Subsequent changes improved the Blaney-Criddle formula by adding more weather and crop variables. The availability of data from automated weather stations, after about 1980, that measure more weather input variables has allowed the empirical Blaney-Criddle formula to be replaced by the mechanistic standardized Penman-Monteith equation with an appropriate crop coefficient to calculate Et. The Penman-Monteith equation calculates Et under non-stressed conditions and represents the maximum Et and associated yield of the crop.

Water rights in the western U.S. have historically, and continue to be, adjudicated using variations of the Blaney-Criddle formula. The Blaney-Criddle formula, derived in farmers’ fields under water stress conditions, calculates an Et that is most closely related to average county yields during the years the measurements were taken. But the empirical relationship and the originally derived coefficients are outdated and invalid for today’s agriculture production systems and should be replaced with the Penman-Monteith equation when adjudicating water rights.

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