Atmospheric rivers (ARs) play vital roles in the western United States and related regions globally, not only producing heavy precipitation and flooding, but also providing beneficial water supply. This paper introduces a scale for the intensity and impacts of ARs. Its utility may be greatest where ARs are the most impactful storm type and hurricanes, nor’easters, and tornadoes are nearly nonexistent. Two parameters dominate the hydrologic outcomes and impacts of ARs: vertically integrated water vapor transport (IVT) and AR duration [i.e., the duration of at least minimal AR conditions (IVT ≥ 250 kg m–1 s–1)]. The scale uses an observed or predicted time series of IVT at a given geographic location and is based on the maximum IVT and AR duration at that point during an AR event. AR categories 1–5 are defined by thresholds for maximum IVT (3-h average) of 250, 500, 750, 1,000, and 1,250 kg m–1 s–1, and by IVT exceeding 250 kg m–1 s–1 continuously for 24–48 h. If the AR event duration is less than 24 h, it is downgraded by one category. If it is longer than 48 h, it is upgraded one category. The scale recognizes that weak ARs are often mostly beneficial because they can enhance water supply and snowpack, while stronger ARs can become mostly hazardous, for example, if they strike an area with antecedent conditions that enhance vulnerability, such as burn scars or wet conditions. Extended durations can enhance impacts. Short durations can mitigate impacts.

A case study is presented of an atmospheric river (AR) that produced heavy precipitation in the U.S. Pacific Northwest during March 2005. The study documents several key ingredients from the planetary scale to the mesoscale that contributed to the extreme nature of this event. The multiscale analysis uses unique experimental data collected by the National Oceanic and Atmospheric Administration (NOAA) P-3 aircraft operated from Hawaii, coastal wind profiler and global positioning system (GPS) meteorological stations in Oregon, and satellite and global reanalysis data. Moving from larger scales to smaller scales, the primary findings of this study are as follow: 1) phasing of several major planetary-scale phenomena influenced by tropical-extratropical interactions led to the direct entrainment of tropical water vapor into the AR near Hawaii, 2) dropsonde observations documented the northward advection of tropical water vapor into the subtropical extension of the midlatitude AR, and 3) a mesoscale frontal wave increased the duration of AR conditions at landfall in the Pacific Northwest.

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Infants with congenitally (38) and natally (17) acquired cytomegalovirus infection were prospectively studied by means of virologic and multiple serologic assays. These infections were characterized by chronic viral excretion (measured in years). The quantity of virus excreted in the urine during early infancy was significantly greater in infants who acquired infection in utero, particularly amon those born with overt disease; thereafter, all three groups (congenital symptomatic, congenital asymptomatic, and natal) excreted similar amounts of virus. The patterns of antibody responses, particularly the fluorescent antibody response to the early antigen and the complement-fixing antibody response, further indicated that congenitally infected infants (especially symptomatic ones) bear a greater antigenic burden than do natally infected infants. From a diagnostic standpoint, the test for fluorescent antibody to the late antigen was the most sensitive assay, whereas the test for complement-fixing antibody proved to be the least useful, The indirect hemagglutination assay, although performed only in infants with natal infection, was only slightly less sensitive than the fluorescent antibody procedure; by the former technique, diagnostic rises were detected in all but one infant after the onset of viruria.

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Comparison of 659 pregnant and 202 nonpregnant women with similar demographic characteristics showed overall rates of cervical cytomegalovirus excretion that were identical (9.5% vs. 9.4%) and were surprisingly high, especially since 89% of the pregnant group possessed antibody to cytomegalovirus when admitted to the study. Prevalence of cytomegalovirus among gravidas was significantly lower during the first (1.6%) than during the third (11.3%) trimester. Thus, early pregnancy appeared to exert a suppressive effect on viral excretion that waned with advancing gestation. A similar but less significant occurrence was observed in the two groups with respect to viuria. Increasing age also appeared to suppress the virologic expression of cervical and urinary tract infection, whereas multiparity seemingly produced such an effect only in the cervix. Among both cervical and urinary excreters, a few shed virus thoughout pregnancy, and others shed virus intermittently; however, viral shedding most commonly began in late gestation and frequently continued into the postpartum period. Primary infection was not documented, and antibody status remained unchanged with the advent of viral excretion in most cases. Thus, reactivation of endogenous virus seems the most likely explanation for viral shedding in our population. Similar rates of isolation of Neisseria gonorrhoeae in excreters and nonexcreters further argue against the other major possibility, venereal reinfection.