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Late spring freeze events, a significant agroclimatic hazard, are investigated for Poland. Daily minimum air temperatures from 184 stations for the period 1951-2010 were used to analyze the frequency and conditional probability of late spring freezes. In addition, three classification schemes were employed to investigate the atmospheric circulation responsible for late spring freezes events. The findings suggest that knowledge of the airflow influencing late spring freezes can help to understand the complex historical trends and projected future changes in freeze risk for perennial crops

The 2005 membership survey is the fifth in a series of surveys that has monitored the composition of the AMS since 1975. The responses of the 2005 survey reveal several interesting changes in the educational level, employment characteristics, and personal status of Society members. The proportion of members with Ph.D. degrees has increased with time to 46% of the regular (nonstudent) and retired members in 2005. Universities/colleges, the federal government, and radio/TV remain the three most important employers of AMS members, although their relative importance has changed with time, with universities/colleges now employing more members than the federal government. Most AMS members continue to report that they became interested in the atmospheric sciences in either elementary school or as undergraduates, although the importance of early (K-6) experiences has increased with time. The age distribution of AMS members in 2005 suggests that the gradual aging of the AMS membership reported earlier (based on the responses to the 1993 and 1999 surveys) is no longer evident. The 2005 survey results also suggest that the percentage of women in the AMS, although still small, has nearly doubled since 1999. However, there has not been comparable progress in increasing the ethnic diversity of the AMS membership. This paper is the first of a series, each focusing on a particular aspect of the survey results.

Heavy precipitation is one of the most significant natural hazards in the United States today. Knowledge of the climatography, including the temporal characteristics, of this phenomenon is necessary in order to better plan, design for, and predict this hazard. In this study, cluster analysis is used to simplify and clarify the spatial patterns in the time of day heavy precipitation most ferquently occurs. Regions with similar diurnal properties are delineated, and the substantial seasonal fluctuations in the regional patterns are traced. Of particular interest is the expansion during the cool season and contraction during the warm season of the nocturnal precipitation regime in the central United States. Key Words: heavy precipitation, climatography, diurnal, United States, seasonality

The persistence of high values of relative humidity for several hours to a few days has wide‐ranging implications for natural and human systems. Among its many impacts, persistent high relative humidity contributes to reduced atmospheric visibility, fog frequency and duration, road and powerline icing, the occurrence of foliar plant disease and the temperature at which heat‐related morbidity and mortality can occur. Despite this, the characteristics of humidity spells—including shifts with climate change—are rarely investigated and consequently poorly understood. Hourly relative humidity, precipitation and temperature for 35 locations in the Lower Peninsula (LP) of Michigan during 2003–2017, and for seven locations during 1973–2017, were used to assess, by biweekly periods, spatial, intra‐annual and inter‐annual variations in the characteristics of relative humidity spells. Two humidity thresholds that accommodate a wide range of applications were used: (1) high relative humidity (HRH), defined as hourly values ≥60%, and extremely high relative humidity (EHRH), defined as hourly values ≥85%. Extended HRH and EHRH spells are frequent across the LP, with HRH spells often spanning 36 hr or longer and EHRH spells commonly persisting more than 12 hr. The probability of HRH and EHRH spells generally decreased with time during 1973–2017, particularly later in the period. Although most spells initiate in the late afternoon and early evening hours, this diurnal preference is less evident as spell length increases, especially for EHRH spells. Furthermore, precipitation is more likely to occur with EHRH spells compared to HRH spells. The orientation and strength of spatial gradients in average annual spell frequency are highly dependent on the choice of humidity and duration thresholds and the temperatures accompanying the spells. This study represents the first comprehensive analysis of the persistence of humidity spells and illustrates the potential usefulness of temporally‐flexible climatological summaries relevant for a wide range of applications. [ABSTRACT FROM AUTHOR]