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MARK J. SCHROEDER

Abstract

Probability terms, especially in relation to precipitation occurrence, were incorporated in fire-weather forecasts on a trial basis in the Chicago District during the 1952 fire-weather seasons. These forecasts were verified in an attempt to determine whether or not such subjective estimates of probability were feasible. Results show that forecasters have some skill in assessing the probability of the occurrence of precipitation especially for the first 30 hours.

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Mark J. Schroeder

In east-facing canyons in the coastal mountains of California, the daytime thermal up-canyon winds are frequently replaced, usually in early afternoon, by a moderately strong down-canyon wind. The same type of wind has also been noted in the western foothills of the Sierra Nevada. This shift in the wind to down canyon is important in wildland fire control and has been a factor in some fire-fighting fatalities. Results of a fire-climate survey conducted in northwestern San Diego County to study these winds show that, in the summer and early fall of 1959, winds switched to down canyon in the afternoon on about one-quarter of the days. From the surface records and a few double-theodolite and airplane observations, a diagrammatic model of this phenomenon has been constructed. The stability of the lower atmosphere along the coast was closely related to the occurrence of down-canyon winds in the area studied. The possibility of making short-range predictions exists by using this relationship along with other considerations.

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Mark J. Schroeder
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Mark J. Schroeder

The question arises as to whether periods of critical burning conditions in the Lake States are associated with any particular weather types. In this study only the spring fire season was considered, and by means of composite maps it is shown that the Hudson Bay High is the principal weather type associated with periods of very high burning index in the month of May. A typical case of a Hudson Bay High weather sequence is then discussed.

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MARK J. SCHROEDER and CLIVE M. COUNTRYMAN

Abstract

In the summer of 1957, short-term weather surveys were made in four prescribed burn areas in the central Sierra Nevada foothills and in the central Coast Range in California The local fireclimate patterns were studied, a fire-weather forecast was adapted to the burn area for each fire, and attempts were made to note the effects of the fires on the fireclimate patterns. This paper describes the survey techniques used, gives an example of a forecast, and discusses some of the survey results. The latter include an increase in wind speed blowing out of the lee side of the fire, effects of the broadscale weather on the local patterns, down-canyon afternoon winds in east-facing canyons, and temperature observations and topographic effects on the lee side of a ridge.

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Morris H. McCutchan and Mark J. Schroeder

Abstract

Stepwise discriminant analysis of eight meteorological variables was used to classify the days from May through September, 1970, on the southern slopes of the San Bernardino Mountains and over the adjacent basin of southern California. The five classes were: 1) hot, dry continental air throughout the day (Santa Ana); 2) relatively dry forenoon, modified marine air in afternoon, very hot (heat wave); 3) moist, modified marine air, hot in afternoon; 4) moist, modified marine air, warm in afternoon; and 5) cool, moist, deep marine air throughout day. Observations of surface temperature, humidity, wind speed and direction, and total oxidant were recorded continuously along the southern slope and crest of the San Bernardino Mountains, and rawinsonde observations were recorded at the base. Vertical profiles of temperature, humidity, and wind measured by rawinsonde document the five classes. Significant differences in fire weather and oxidant air pollution exposure were found on the slope and crest during the five meteorological conditions. Oxidant concentrations are highest on days in classes 2, 3 and 4, when transported up the slope with the marine air during the day.

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Michael A. Fosberg and Mark J. Schroeder

Abstract

Three-dimensional analysis shows the sea-breeze front to be primarily a wind shift line in which the thermal discontinuity lags behind the shear line and becomes quasi-stationary in the afternoon. Two synoptic patterns control the temperature regime. On cool days, when a high level trough is present the sea-breeze front is weak, moves rapidly and penetrates far inland; the marine layer is deep and the sea breeze spills over the low mountain ridges. Warm days occur, when the Pacific high penetrates into Oregon and Washington; the marine layer is shallow and the sea-breeze front is intense and slow moving.

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Joshua J. Schroeder, David A. R. Kristovich, and Mark R. Hjelmfelt

Abstract

The first detailed observations of the interaction of a synoptic cyclone with a lake-effect convective boundary layer (CBL) were obtained on 5 December 1997 during the Lake-Induced Convection Experiment. Lake-effect precipitation and CBL growth rates were enhanced by natural seeding by snow from higher-level clouds and the modified thermodynamic structure of the air over Lake Michigan due to the cyclone. In situ aircraft observations, project and operational rawinsondes, airborne radar, and operational Weather Surveillance Radar-1988 Doppler data were utilized to document the CBL and precipitation structure for comparison with past nonenhanced lake-effect events. Despite modest surface heat fluxes of 100–200 W m−2, cross-lake CBL growth was greatly accelerated as the convection merged with an overlying reduced-stability layer. Over midlake areas, CBL growth rates averaged more than twice those previously reported for lake-effect and oceanic cold-air outbreak situations. Regions of the lake-effect CBL cloud deck were seeded by precipitation from higher-level clouds over the upwind (western) portions of Lake Michigan before the CBL merged with the overlying reduced-stability layer. In situ aircraft observations suggest that in seeded regions, the CBL was deeper than in nonseeded regions. In addition, average water-equivalent precipitation rates for all of the passes with seeded regions were more than an order of magnitude greater in seeded regions than nonseeded regions because of higher concentration of snow particles of all sizes. A maximum snowfall rate of 4.28 mm day−1 was calculated using aircraft particle observations in seeded regions, comparable to snowfall rates previously reported for lake-effect events, often with much larger surface heat fluxes, but not interacting with synoptic cyclones.

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Brian C. Zachry, John L. Schroeder, Andrew B. Kennedy, Joannes J. Westerink, Chris W. Letchford, and Mark E. Hope

Abstract

Over the past decade, numerous field campaigns and laboratory experiments have examined air–sea momentum exchange in the deep ocean. These studies have changed the understanding of drag coefficient behavior in hurricane force winds, with a general consensus that a limiting value is reached. Near the shore, wave conditions are markedly different than in deep water because of wave shoaling and breaking processes, but only very limited data exist to assess drag coefficient behavior. Yet, knowledge of the wind stress in this region is critical for storm surge forecasting, evaluating the low-level wind field across the coastal transition zone, and informing the wind load standard along the hurricane-prone coastline. During Hurricane Ike (2008), a Texas Tech University StickNet platform obtained wind measurements in marine exposure with a fetch across the Houston ship channel. These data were used to estimate drag coefficient dependence on wind speed. Wave conditions in the ship channel and surge level at the StickNet location were simulated using the Simulating Waves Nearshore Model coupled to the Advanced Circulation Model. The simulated waves were indicative of a fetch-limited condition with maximum significant wave heights reaching 1.5 m and peak periods of 4 s. A maximum surge depth of 0.6 m inundated the StickNet. Similar to deep water studies, findings indicate that the drag coefficient reaches a limiting value at wind speeds near hurricane force. However, at wind speeds below hurricane force, the drag coefficient is higher than that of deep water datasets, particularly at the slowest wind speeds.

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Mark J. Schroeder, Michael A. Fosberg, Owen P. Cramer, and Clyde A. O'Dell

This paper reviews the literature on the main aspects of marine air invasion on the Pacific coast. In particular, it considers the sea breeze, Pacific coast monsoon, and airflow over coastal mountains. The major problems associated with marine air invasion are: 1) the relationship of microscale convection, waves, and banded convection- waves to the sea-breeze energetics and sea-breeze front, 2) the interaction of energy forming and dissipating processes from the general circulation down to the micrometeorological scale, 3) the climatology and dynamics of the monsoon, and 4) the mechanism of the lee waves observed in the lee of the heated coastal mountains. Lee waves often form in a statically unstable atmosphere.

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