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- Author or Editor: Lance F. Bosart x
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Abstract
An analysis of skill in predicting daily temperature and precipitation is presented for six years (1969–1975) of forecasts made for the Albany County Airport by students and faculty in the Department of Atmospheric Science of the State University of New York at Albany. The daily consensus forecast (made up by averaging the forecasts of all forecasters) shows no significant secular increase in skill for temperature. An apparent increase in the consensus skill in precipitation forecasting is noted with most of the increase occurring in the spring 1972 semester. Possible reasons for this increase are discussed. The skill (defined as the percentage improvement over a persistence climatological forecast) of the ensemble of forecasters over a persistence climatological control is near 50% for the first day decaying to 10% and near zero by the 3rd and 4th day for precipitation and to just under 10% for temperature by the 4th day. These results are consistent with the results presented by Sanders (1973).
Some relationship is found for skill to be a function of the variability of the daily temperature about the climatological mean. Skill, however, appears to be insensitive to the frequency of days with radiational cooling, a major local forecast problem. likewise skill appears to be independent of daily rainfall amount or frequency. These findings are consistent with those found for Boston by Sanders (1973).
Finally, the trend towards a plateau in skill noted by Sanders (1973) is confirmed for a different location.
Abstract
An analysis of skill in predicting daily temperature and precipitation is presented for six years (1969–1975) of forecasts made for the Albany County Airport by students and faculty in the Department of Atmospheric Science of the State University of New York at Albany. The daily consensus forecast (made up by averaging the forecasts of all forecasters) shows no significant secular increase in skill for temperature. An apparent increase in the consensus skill in precipitation forecasting is noted with most of the increase occurring in the spring 1972 semester. Possible reasons for this increase are discussed. The skill (defined as the percentage improvement over a persistence climatological forecast) of the ensemble of forecasters over a persistence climatological control is near 50% for the first day decaying to 10% and near zero by the 3rd and 4th day for precipitation and to just under 10% for temperature by the 4th day. These results are consistent with the results presented by Sanders (1973).
Some relationship is found for skill to be a function of the variability of the daily temperature about the climatological mean. Skill, however, appears to be insensitive to the frequency of days with radiational cooling, a major local forecast problem. likewise skill appears to be independent of daily rainfall amount or frequency. These findings are consistent with those found for Boston by Sanders (1973).
Finally, the trend towards a plateau in skill noted by Sanders (1973) is confirmed for a different location.
Abstract
Detailed hourly precipitation patterns are analyzed for two major winter U.S. east coast storms that exhibited considerable mesoscale features. Pronounced spatial and temporal continuity is noted for individual convective rainfalls within the cold air. Such features can also be tracked in the wind and pressure fields. Finally, some thoughts are offered on the possible dynamic significance of organized mesoscale precipitation patterns, along with comments relevant to the forecasting of such patterns.
Abstract
Detailed hourly precipitation patterns are analyzed for two major winter U.S. east coast storms that exhibited considerable mesoscale features. Pronounced spatial and temporal continuity is noted for individual convective rainfalls within the cold air. Such features can also be tracked in the wind and pressure fields. Finally, some thoughts are offered on the possible dynamic significance of organized mesoscale precipitation patterns, along with comments relevant to the forecasting of such patterns.
Abstract
Average kinematic vertical motion and relative vorticity profiles are presented for a long-lived midlatitude convective complex. A breakdown into active convective and stratiform precipitation regions shows very good agreement in the vertical motion profiles with published results for tropical convective systems.
Abstract
Average kinematic vertical motion and relative vorticity profiles are presented for a long-lived midlatitude convective complex. A breakdown into active convective and stratiform precipitation regions shows very good agreement in the vertical motion profiles with published results for tropical convective systems.
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No Abstract available.
Abstract
A case study is made of a period of exceptional warmth in the mid and upper troposphere over the Carib-bean from 19–21 February 1964. The case is a good example of intense winter interaction of mid-latitude and tropical circulations during which lateral forcing from higher latitudes appears to play a prominent role. For example, at 500 mb, temperatures of −1 to −2C which exhibited spacial and temporal continuity on the synoptic scale were noted. These values were more than three standard deviations warmer than monthly mean values and occurred in association with a strong low-latitude polar jet along the Gull Coast of the United States.
Isentropic trajectories document average 12-hr descent rates of up to 2 cm sec−1 in the vicinity of 15N in association with the warmth area. Criteria for inertial instability is satisfied over a portion of the anti-cyclonic flank of the strong jet stream leading to a speculative case for a transverse thermally indirect circulation such that a persistent anticyclone north of Puerto Rico is strengthened. Reed and Vleck's hypothesis on the annual temperature cycle of the tropical lower stratosphere is examined on a limited basis with daily data both directly and indirectly with rather inconclusive results.
Abstract
A case study is made of a period of exceptional warmth in the mid and upper troposphere over the Carib-bean from 19–21 February 1964. The case is a good example of intense winter interaction of mid-latitude and tropical circulations during which lateral forcing from higher latitudes appears to play a prominent role. For example, at 500 mb, temperatures of −1 to −2C which exhibited spacial and temporal continuity on the synoptic scale were noted. These values were more than three standard deviations warmer than monthly mean values and occurred in association with a strong low-latitude polar jet along the Gull Coast of the United States.
Isentropic trajectories document average 12-hr descent rates of up to 2 cm sec−1 in the vicinity of 15N in association with the warmth area. Criteria for inertial instability is satisfied over a portion of the anti-cyclonic flank of the strong jet stream leading to a speculative case for a transverse thermally indirect circulation such that a persistent anticyclone north of Puerto Rico is strengthened. Reed and Vleck's hypothesis on the annual temperature cycle of the tropical lower stratosphere is examined on a limited basis with daily data both directly and indirectly with rather inconclusive results.
Consensus (the average of all forecasts) skill levels in forecasting daily maximum and minimum temperature, precipitation probability across six class intervals, and precipitation amount at the State University of New York at Albany are reviewed for the period 1977–82. Skill is measured relative to a climatological control. Forecasts are made for four consecutive 24 h periods for Albany, N.Y., beginning at 1800 GMT of the current day.
For minimum temperature, the skill levels average 57%, 41%, 26%, and 15%, respectively, for 24, 48, 72, and 96 h in advance. For maximum temperature, a more limited sample yields corresponding skill levels of 84%, 49%, 34%, and 19% for 12, 36, 60, 84 h ahead. Linear regression analysis yields little in the way of a definitive trend, given the smallness of the explained variance. Comparison with other readily available objective and subjective operational guidance establishes the credibility of the consensus forecast.
Consensus (the average of all forecasts) skill levels in forecasting daily maximum and minimum temperature, precipitation probability across six class intervals, and precipitation amount at the State University of New York at Albany are reviewed for the period 1977–82. Skill is measured relative to a climatological control. Forecasts are made for four consecutive 24 h periods for Albany, N.Y., beginning at 1800 GMT of the current day.
For minimum temperature, the skill levels average 57%, 41%, 26%, and 15%, respectively, for 24, 48, 72, and 96 h in advance. For maximum temperature, a more limited sample yields corresponding skill levels of 84%, 49%, 34%, and 19% for 12, 36, 60, 84 h ahead. Linear regression analysis yields little in the way of a definitive trend, given the smallness of the explained variance. Comparison with other readily available objective and subjective operational guidance establishes the credibility of the consensus forecast.
Abstract
During the period 26–29 May 1968 a shallow cyclonic circulation, known 1ocally as a Catalina eddy, developed in the offshore waters of southern California. A synoptic and mesoscale analysis of the event establishes the following: 1) the incipient circulation forms on the coast near Santa Barbara downwind of the coastal mountains, 2) cyclonic shear vorticity appears offshore in response to lee troughing downstream of the coastal mountains between Vandenberg and Pt. Mugu, California, 3) mountain wave activity may be aiding incipient eddy formation in association with synoptic-scale subsidence and the generation of a stable layer new the crest of the coastal mountains, 4) a southeastward displacement and offshore expansion of the circulation occurs following the passage of the synoptic-scale ridge line, and 5) dissipation of the eddy occurs with the onset of a broad onshore flow.
Abstract
During the period 26–29 May 1968 a shallow cyclonic circulation, known 1ocally as a Catalina eddy, developed in the offshore waters of southern California. A synoptic and mesoscale analysis of the event establishes the following: 1) the incipient circulation forms on the coast near Santa Barbara downwind of the coastal mountains, 2) cyclonic shear vorticity appears offshore in response to lee troughing downstream of the coastal mountains between Vandenberg and Pt. Mugu, California, 3) mountain wave activity may be aiding incipient eddy formation in association with synoptic-scale subsidence and the generation of a stable layer new the crest of the coastal mountains, 4) a southeastward displacement and offshore expansion of the circulation occurs following the passage of the synoptic-scale ridge line, and 5) dissipation of the eddy occurs with the onset of a broad onshore flow.
Abstract
On 18–19 February 1979 a major east coast cyclone deposited a record-breaking snowfall on the Middle Atlantic States. The storm is noteworthy because of the failure of the operational prediction models to signal the intensity of the event. The life cycle of the cyclone is reviewed with emphasis on the synoptic and mesoscale features and their possible linkage.
Prior to cyclogenesis the synoptic pattern features a massive cold anticyclone near the Great Lakes with a broad baroclinic zone extending from Texas eastward to the Atlantic coast. A region of enhanced lower tropospheric baroclinicity develops along the Carolina coastal strip in response to significant oceanic sensible and latent heat fluxes which warm, moisten and destabilize the boundary layer. Cyclogenesis is initiated along the coastal front as the result of lower tropospheric warm advection. The importance of the coastal front is that it effectively steers the cyclone north-northeastward parallel to the coast such that it eventually acquires a favorable phase relationship for deepening with respect to a vigorous short-wave trough moving eastward from the Ohio Valley by 1200 GMT 19 February.
Explosive deepening takes place in the ensuing 6 h coincident with the outbreak of convection near the storm center. By 1800 GMT, satellite pictures reveal a closed, clear storm eye while surface ship and drilling rig data disclose the presence of minimal hurricane force winds, primarily in the northern semicircle of the storm. Unlike a hurricane, however, the convection is asymmetric with respect to the vortex, being concentrated in the region of strongest surface winds.
The major operational model errors stem from poor sea level pressure and quantitative precipitation prognoses. Evidence is presented that initial analysis deficiencies coupled with inadequate boundary-layer and convective precipitation physics precluded a successful model forecast in this cam.
Abstract
On 18–19 February 1979 a major east coast cyclone deposited a record-breaking snowfall on the Middle Atlantic States. The storm is noteworthy because of the failure of the operational prediction models to signal the intensity of the event. The life cycle of the cyclone is reviewed with emphasis on the synoptic and mesoscale features and their possible linkage.
Prior to cyclogenesis the synoptic pattern features a massive cold anticyclone near the Great Lakes with a broad baroclinic zone extending from Texas eastward to the Atlantic coast. A region of enhanced lower tropospheric baroclinicity develops along the Carolina coastal strip in response to significant oceanic sensible and latent heat fluxes which warm, moisten and destabilize the boundary layer. Cyclogenesis is initiated along the coastal front as the result of lower tropospheric warm advection. The importance of the coastal front is that it effectively steers the cyclone north-northeastward parallel to the coast such that it eventually acquires a favorable phase relationship for deepening with respect to a vigorous short-wave trough moving eastward from the Ohio Valley by 1200 GMT 19 February.
Explosive deepening takes place in the ensuing 6 h coincident with the outbreak of convection near the storm center. By 1800 GMT, satellite pictures reveal a closed, clear storm eye while surface ship and drilling rig data disclose the presence of minimal hurricane force winds, primarily in the northern semicircle of the storm. Unlike a hurricane, however, the convection is asymmetric with respect to the vortex, being concentrated in the region of strongest surface winds.
The major operational model errors stem from poor sea level pressure and quantitative precipitation prognoses. Evidence is presented that initial analysis deficiencies coupled with inadequate boundary-layer and convective precipitation physics precluded a successful model forecast in this cam.
