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Gary S. Wojcik and Daniel S. Wilks

Abstract

The sensitivity of temperature forecast biases to the presence or absence of snow cover is investigated for the December–March periods of 1985–1986 and 1986–87 at ten stations in the northeastern United States. Forecast biases are consistently “warmer” for snow-covered (defined here as ≥2″) versus open conditions in situations where the MOS forecast equations do not include snow cover as an explicit predictor. The differences are most often statistically significant for the forecasts of minimum temperature. However, this aspect of forecast performance is superimposed on a general cold bias for both maximum and minimum temperature forecasts, and the two effects tend to cancel for snow-covered conditions. No significant differences in forecast bias between snow-covered and open conditions are found for the few cases where snow cover is included explicitly as a predictor in the MOS forecast equations.

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Gary S. Wojcik and David R. Fitzjarrald

Abstract

Atmospheric conditions for several days after concrete is poured influence the exothermic, temperature-dependent, hydration reactions of concrete's cementitious (binding) components. Because excessively high concrete temperatures or lack of water eventually can lead to cracking, the initial days are critical to determining the concrete's long-term durability. Accurate model forecasts of concrete temperatures and moisture would help engineers to determine an optimal time to pour. Such forecasts require adequate environmental predictions. Existing models of curing concrete bridge decks employed by engineers lack realistic boundary conditions and so cannot handle many atmospheric conditions. Atmospheric energy exchange parameterizations typically are intended for use over areas much larger than bridges and so may not be useful as boundary conditions in curing-concrete models. To determine proper boundary conditions for the curing-concrete model discussed here, energy balances of four curing concrete bridge decks were estimated from observations made in the atmosphere as well as inside the concrete. Common meteorological techniques to estimate energy balance terms were used to bound the estimates. Most (70%–85%) of the concrete heat transfer occurred at the bridge's top. Sensible, latent, net radiative, and runoff water (sprayed on the top surface) heat fluxes, respectively, contributed 6%–24%, 15%–58%, 10%–34%, and 0%–73% of the top surface heat transfer. Bottom heat transfer was less than 30% of the top surface transfer. Laboratory calorimetry and the energy balance results agree to within 20% that the hydration reactions evolved about 190 kJ kg−1 by 24 h after mixing. This agreement validates the exchange coefficients proposed for the heat and moisture balances of these small areas both during periods when the concrete generated heat and later when the concrete was more passive in its environment.

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