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Mitchell W. Moncrieff, Duane E. Waliser, Martin J. Miller, Melvyn A. Shapiro, Ghassem R. Asrar, and James Caughey

Newell 1994 ; Ralph et al. 2011 ). The rivers are associated with the incursion of midlatitude fronts, the extratropical transition of tropical cyclones, and the remote effects of planetary waves emanating from the tropics. On seasonal time scales, the Asian-Australian monsoon and its intraseasonal variability strongly modulates the distribution of atmospheric water. Global models have great difficulty in reproducing such variability. Scale gap and missing mesoscale in climate models. Traditional

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William J. Merryfield, Johanna Baehr, Lauriane Batté, Emily J. Becker, Amy H. Butler, Caio A. S. Coelho, Gokhan Danabasoglu, Paul A. Dirmeyer, Francisco J. Doblas-Reyes, Daniela I. V. Domeisen, Laura Ferranti, Tatiana Ilynia, Arun Kumar, Wolfgang A. Müller, Michel Rixen, Andrew W. Robertson, Doug M. Smith, Yuhei Takaya, Matthias Tuma, Frederic Vitart, Christopher J. White, Mariano S. Alvarez, Constantin Ardilouze, Hannah Attard, Cory Baggett, Magdalena A. Balmaseda, Asmerom F. Beraki, Partha S. Bhattacharjee, Roberto Bilbao, Felipe M. de Andrade, Michael J. DeFlorio, Leandro B. Díaz, Muhammad Azhar Ehsan, Georgios Fragkoulidis, Sam Grainger, Benjamin W. Green, Momme C. Hell, Johnna M. Infanti, Katharina Isensee, Takahito Kataoka, Ben P. Kirtman, Nicholas P. Klingaman, June-Yi Lee, Kirsten Mayer, Roseanna McKay, Jennifer V. Mecking, Douglas E. Miller, Nele Neddermann, Ching Ho Justin Ng, Albert Ossó, Klaus Pankatz, Simon Peatman, Kathy Pegion, Judith Perlwitz, G. Cristina Recalde-Coronel, Annika Reintges, Christoph Renkl, Balakrishnan Solaraju-Murali, Aaron Spring, Cristiana Stan, Y. Qiang Sun, Carly R. Tozer, Nicolas Vigaud, Steven Woolnough, and Stephen Yeager

supporting progressively higher resolution and larger ensembles that allow uncertainties to be better estimated and, in some cases, reduced. F ig . 1. Schematic depiction of (bottom) temporal ranges and (top) sources of predictability for weather and climate prediction. The subseasonal range encompasses the S2S time scales and the seasonal and annual-to-decadal ranges encompass the S2D time scales that are considered in this paper. Longer multidecadal and centennial ranges derive predictability mainly

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Andrew Hoell, Britt-Anne Parker, Michael Downey, Natalie Umphlett, Kelsey Jencso, F. Adnan Akyuz, Dannele Peck, Trevor Hadwen, Brian Fuchs, Doug Kluck, Laura Edwards, Judith Perlwitz, Jon Eischeid, Veva Deheza, Roger Pulwarty, and Kathryn Bevington

understanding of the severity of the 2017 northern Great Plains flash drought requires a comparison to historical conditions in the region. Notably, the speed of land surface drying, an up-to-80th-percentile soil moisture decline for the 3-week period beginning on 18 May 2017, was among the quickest such standardized decreases since at least 1916 ( Fig. 2a ). Rapid soil moisture declines over the U.S. northern Great Plains have a distinct seasonality, as approximately 50%–80% of the top percentile of 3-week

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F. Briscoe Stephens

In a study of the effects of weather upon the consumption of electricity in a power network, it was found that large-scale load variations generally mask the effects of weather and make it almost impossible to obtain practical results from a comparison of the load data in their original form. A simple method is presented by which the effects of a seasonal trend and of major load shifts, caused by changing activities in a community, can be eliminated. This method makes it possible to analyze load data for possible weather effects, even though the consumer demand for electric power may change considerably during the period for which the study is being made.

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Alan Robock

While tropical sea surface temperatures certainly influence the atmosphere; winter circulation, temperature, and precipitation over Northen Hemisphere continents are also influenced by circulation patterns related to the stratosphere. In particular, large tropical volcanic eruptions produce winter warming patterns over Northern Hemisphere continents because of a dynamical effect forced by gradients of radiative heating from sulfate aerosols in the lower stratosphere. These effects must be included for accurate dynamical seasonal predictions of Northern Hemisphere winter temperature over both North America and Eurasia.

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Elmar R. Reiter

Mountain ranges and high plateaus influence atmospheric circulation patterns on all scales, ranging from ultralong planetary waves to small turbulent eddies. Some of these effects are brought about simply by orographic obstacles acting as barriers to the flow. Of equal importance, however, are the thermal effects of elevated land masses, which can generate considerable baroclinicity. Various time scales have to be considered in the thermal forcing of the atmosphere by large elevated land masses. Diurnal variations of the heating and cooling cycle have been shown to be prominent factors over Tibet. On time scales from days to weeks, the Northern Hemisphere plateaus seem to influence the monsoon circulations. There are strong indications that interseasonal “memory” exists in the heat balance of plateaus that might affect seasonally abnormal monsoon behavior. Such “memory” could be caused by feedback between thermal effects of land masses and “near-resonant” planetary waves.

In order to assess the thermal impact of mountains and plateaus, we need considerably more detailed knowledge of the energy transfer processes between the valley atmosphere, the yet poorly delineated planetary boundary layer over mountains, and the “free atmosphere.” To achieve such knowledge, experimental and theoretical studies involving micro-, meso-, and macroscales will have to intermesh more closely than in the past.

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Stanley A. Changnon Jr.

Collection of precipitation in a raingage located in Lake Michigan near Chicago over an 11-yr period has permitted a study of the average monthly, seasonal and annual precipitation received off the southwestern shore of the lake. These values are compared with average precipitation occurring in the Chicago urban area and with amounts from other nearby rural and shore stations. From these comparisons, the effects of lake and urban influences on the precipitation pattern are evaluated.

The results of this study compare favorably with results from similar lake-precipitation studies performed by the Corps of Engineers. The precipitation data from this station in the lake indicate that precipitation over southern Lake Michigan may be considerably less than previously estimated from data of stations along the shore. The effect of precipitation on lake levels may be better evaluated now that additional information on lake precipitation is available.

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Raymond P. Motha and Thomas R. Heddinghaus

The Joint Agricultural Weather Facility (JAWF), a cooperative effort between the Climate Analysis Center, NMC/NWS/NOAA (National Meteorological Center/National Weather Service/National Oceanic and Atmospheric Administration) and the World Agricultural Outlook Board, U.S. Department of Agriculture (USDA), focuses on weather anomalies and their effects on the crop-yield potential in major international crop areas. The basic mission is to provide an objective procedure for translating the flow of global weather information into timely and accurate assessments of growing-season conditions which ultimately impact on global agricultural production and trade. Daily monitoring of satellite weather images and meteorological data provides the framework for agricultural weather analysis. Daily, weekly, and seasonal summaries are processed and merged with historical weather and crop data for evaluation of the crop-yield potential. Information is disseminated at routine briefings, in written summaries, and through informal discussions.

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Mark Russo, David Changnon, Mike Podolak, Hugh Freestrom, and Jon B. Davis

The El Niño-Southern Oscillation (ENSO) phenomenon explains some of the interannual climate variability in many tropical and midlatitude regions. It is important in developing more accurate seasonal climate forecasts and thus in aiding long-range weather-sensitive decision making in various sectors.

The degree to which ENSO information could forecast one of three classes of seasonal cooling degree days (CDD) and heating degree days (HDD) was examined using 1) the magnitude of the ENSO event during a given season, 2) the preseason rate of change of sea surface temperature (SSTs) (December–May for summers and June–October for winters), and 3) the effects of strong winter ENSO events on future seasons. All three ENSO-related indices were based on monthly equatorial Pacific SST anomalies in the Niño-3.4 region. Regional probabilities of each HDD/CDD category (above, average, and below) were determined for each ENSO predictive index. The highest probability of experiencing an HDD/CDD anomaly occurs with strong preseason SST trends. When presummer SST cooling occurs, the northeast and midcontinent experience above-average CDD (80% and 75%, respectively). Other interesting relationships were found between strong winter ENSO events and ensuing HDD/CDD anomalies. These results suggest that utility-based decision makers who can utilize enhanced climate information may reap benefits during particular years by integrating the ENSO information into their models. This study was part of a special student training experiment conducted at Northern Illinois University.

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T. Rossby and E. Gottlieb

An overview of the first 4.5 years of operation of a program to monitor the structure and variability of the Gulf Stream (GS) is presented. A container vessel that operates on a weekly schedule between Port Elizabeth, New Jersey, and Hamilton, Bermuda, is equipped with a 150-kHz narrowband acoustic Doppler current profiler to measure currents from the surface to ~300 m depth. A major objective of the multiyear program is to study the annual cycle and interannual variations in velocity structure and transport by the GS. In this survey the focus is on the transport and lateral structure of the current at 52-m depth.

The velocity maximum is constant at 2.07 ± 0.24 m s−1 (4 kt) with a seasonal range of ~0.1 m s−1 . Seasonal and interannual variations in total transport are observed but appear to be limited to the edges of the current, apparently reflecting low-frequency variations in the intensity of the recirculating waters adjacent to the stream. The transport by the central core of the current, defined as those waters moving at 1 m s−1 or faster, equals 0.9 × 105 m2 s−1 , has no seasonal signal, and is constant to within a few percent when averaged in half-year intervals. If the central core of the current is viewed as “insolated” from the effects of meandering, this result implies substantial stability to the large-scale wind-driven and thermohaline circulations during the observation program. Variations in poleward heat transport probably originate less in the GS and more from changing heat loss patterns at higher latitudes.

Other issues concerning the potential vorticity field and energy conversion rates are also discussed. This ongoing program illustrates the role commercially operated vessels can play in making repeat observations of the velocity structure (and other parameters) of the ocean on a regular basis.

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