Search Results

You are looking at 1 - 10 of 13 items for

  • Author or Editor: Gregory P. Byrd x
  • All content x
Clear All Modify Search
Gregory P. Byrd

Abstract

Biases in mean temperatures due to differing times of daily maximum and minimum temperature observation cause problems in evaluation of temporal and spatial anomalies in temperature and derived degree day values. These biases were examined using six years (1973–78) of digitized hourly temperature data taken at Oneonta, New York. An annual mean temperature difference of 2.5°F is noted between means computed with the 0600 LST and 1500 IST observation times, with individual monthly differences as high as 4.4°F. Maximum seasonal degree day biases were 743 heating degree days (HDD) (10.2%), 169 cooling degree days (CDD) (43.3%), and 299 growing degree days (GDD) (14.3%).

A modified version of the Blackburn method for adjusting mean temperature data for observation time bias is presented. The modified method involves adjusting data to a “true” mean obtained by averaging all hourly temperature values for the 24-hour period ending at midnight, rather than adjusting to the midnight standard observational mean obtained by averaging the maximum and minimum values over the same period. The adjustments are applied to mean temperatures from stations with different observation times in the region around Oneonta, resulting in spatial analysis fields which are believed to be more representative than those using the published data. This suggests that application of such an adjustment scheme results in a more homogeneous climatological data set.

Full access
Gregory P. Byrd

Abstract

This investigation presents an extensive analysis of precipitation bands associated with winter season “over-running” events in the southern plains of the United States. The primary motivation is an investigation of the relevance of conditional symmetric instability (CSI) theory to overrunning precipitation events. This is accomplished by means of a statistical composite study of events of differing degrees of bandedness, using synoptic sounding and National Weather Service radar data. The composite study shows that it is difficult to distinguish between the environments of banded and nonbanded cases on the basis of individually examined shear and buoyancy parameters. Some statistically significant differences do occur when shear and buoyancy effects are combined in an evaluation of CSI, with more strongly banded events showing greater instability.

Full access
Gregory P. Byrd and Stephen K. Cox

Abstract

Tropospheric radiative convergence profiles from Cox and Griffith are used to assess the radiative forcing upon a tropical cloud cluster located in the vicinity of the GATE A/B-scale array during 4–6 September 1974. A background discussion summarizes some of the previous investigations that served as motivation for the present study. The atmospheric response to differential radiative cooling between the cluster and its surrounding environment is examined by means of “slab” and cross section analyses over the Cox-Griffith array. A radiatively derived vertical motion model is constructed to investigate the role of radiation with respect to larger-scale dynamics during a daytime (0600–1200 LST 5 September) and nighttime (1800–2400 LST 5 September) period of the cluster life cycle.

Radiative forcing is found to be strongest during the initial stages of cluster development. Throughout the cluster life cycle, the radiative forcing is consistently strongest in the middle troposphere (400–700 mb). As the cluster system intensifies, daytime shortwave warming superimposed upon the longwave cooling lessens the total radiative cooling in the surrounding cloud-free region, resulting in a lessening of the differential radiative cooling. Increased amounts of middle and high cloud remnants also contribute to the observed weakening of radiative forcing during the mature and dissipating disturbance stages. Cross section analyses reveal that E-W gradients of radiative convergence between the cluster and its surroundings are comparable in magnitude to the N-S gradients.

The radiatively derived vertical motion model yields a qualitatively realistic total area of cluster influence for a nighttime case, 1800–2400 GMT on 5 September. The model assumption of a closed mass system breaks down during the daytime (0600–1200 LST, 5 September) period, yielding an unrealistically 1arge total area of cluster influence. This suggests the occurrence of significant cluster-scale interactions with large-scale circulations during the daytime period. Radiative forcing appears to play a more significant role in dynamical interactions during the nighttime period, when circulations seem to be somewhat more localized.

The maximum in-cluster precipitation intensity lags the incidence of strong radiative forcing by 6–8 h, in general agreement with GATE composite observations. Continental oceanic differential beating must also play a significant role in modulating cluster- and large-scale dynamical interactions, accounting for the anomalously long precipitation lag observable in the GATE cluster. The interpretations presented herein are based solely upon this single case study and may not necessarily be representative of cluster disturbances as a whole.

Full access
Robert A. Maddox, David J. Stensrud, and Gregory P. Byrd
Full access
Howard B. Bluestein, Eugene W. McCaul Jr., Gregory P. Byrd, and Robert L. Walko

Abstract

A storm intercept crew from the University of Oklahoma made a sounding near and underneath the wall cloud of the right-moving member of a splitting thunderstorm in north Texas on 27 May 1985. A comparison between the sounding and an environmental sounding indicated that the low-level moist layer was moister and much deeper near and underneath the wall cloud.

Full access
Howard B. Bluestein, Eugene W. McCaul Jr., Gregory P. Byrd, and Gary R. Woodall

Abstract

On 7 May 1986 thunderstorms formed during the afternoon near a dryline in the Texas Panhandle under weak synoptic-scale forcing. Five tornadoes and large hail were produced by one storm near Canadian, Texas. The focus of the paper is the analysis of soundings obtained by a storm-intercept crew. A sounding launched into the wall cloud of the storm just after the fourth tornado indicated a nearly pseudomoist adiabatic lapse rate, a temperature excess of 10°C over the environment at 500 mb, and an updraft speed of almost 50 m s−1 near 6 km AGL, in reasonable agreement with parcel theory.

Full access
Gregory P. Byrd, Richard A. Anstett, Joseph E. Heim, and David M. Usinski

Abstract

Measurements of the thermodynamic environments in the vicinity of lake-effect snowbands were obtained during the winter of 1987/88, using portable radiosonde equipment. During the experimental period, a total of 17 soundings were launched on ten field days. These soundings covered both single- and multiple-band events under a variety of conditions, including heavy snowfall rates of up to 13 cm h−1. As expected, the soundings showed moist-adiabatic conditions within the cloud layer with a stable layer at cloud-top level. In an intense single-band case, soundings showed a parcel buoyancy of 2.5°C within the hand at 2 km above ground level (AGL). Furthermore, the base of the inversion within the band was displaced some 0.6 km above that of the surrounding environment. Sensible heating of the low-level air as it flowed over the warm lake is postulated to be the primary source of this temperature surplus. Strong surface convergence and parcel buoyancy within the band apparently combined to produce the overshooting cloud top and the observed heavy snowfall rate. Multiple- band soundings showed little difference between the thermodynamic environments within and adjacent to the bands. Analysis of the soundings indicates that the depth of the mixed layer may be of greater importance than the strength of instability in determining the intensity of lake-effect precipitation.

Full access
Howard B. Bluestein, Eugene W. McCaul Jr., Gregory P. Byrd, and Gary R. Woodall

Abstract

No abstract available.

Full access
Howard B. Bluestein, Eugene W. McCaul Jr., Gregory P. Byrd, Robert L. Walko, and Robert Davies-Jones

Abstract

This is a case study of deep, but narrow convective towers which split twice into right- and left-moving components in southwestern Oklahoma on 28 May 1985. Our analysis makes use of storm-intercept visual documentation, mobile soundings, surface mesonetwork data, and frequent soundings from special sites. The data show that the convective towers behaved in many respects like low-precipitation storms, having formed in an environment of large CAPE and moderately strong unidirectional shear. The observation of towers splitting even when there is no heavy precipitation at the surface implies that rain processes are not crucial to the splitting phenomenon. The tiny storms were confined to a region northeast of a surface cyclone and low-pressure area, near the intersection of the dryline and an old outflow boundary, where convective temperature was reached. Evidence is presented that the moist layer was deepened locally just prior to convective initiation, and that the deepening was related to low-level convergence associated with the westward motion of the dryline.

Full access
Robert J. Ballentine, Alfred J. Stamm, Eugene E. Chermack, Gregory P. Byrd, and Donald Schleede

Abstract

The Pennsylvania State University–NCAR Mesoscale Model version 5 (MM5), running on a triply nested grid, was used to simulate the intense lake-effect snowstorm of 4–5 January 1995. On the finest grid (5-km resolution) centered over Lake Ontario, MM5 produced a snowband in the correct location having a size and orientation similar to the band observed by the WSR-88D radar at Binghamton, New York. The simulated precipitation distribution agreed well with the observed snowfall during the first 18 h during the time when the snowband was in its midlake position extending into the Tug Hill plateau. During the last 12 h of the simulation, when both the observed and simulated snowbands lay along the south shore of Lake Ontario, the simulated snowfall at inland locations of Oswego County was less than observed. During this period, the simulated precipitation over Lake Ontario appeared to be excessive, although no radar data or ground truth was available to confirm this.

Two short-wave troughs interacted with the Lake Ontario snowband. The temporary weakening of the snowband after passage of the first trough was simulated well in the triply nested MM5 simulation. A comparison was made between the operational Eta Model run and an MM5 simulation on a grid of comparable resolution (80 km) in handling the passage of the second more vigorous short wave. Both the Eta and the 80-km MM5 were a few hours too early with the passage of this trough. The nested-grid version of MM5 was correct in simulating the rapid southward movement of the band to Oswego County just after the second trough moved east of the lake. However, because of the timing error with the trough, MM5 was premature by a few hours in the southward shift of the snowband.

Results on the 15-km grid indicated that moisture plumes from Lake Huron and Georgian Bay fed into the Lake Ontario band. In the lowest few hundred meters, these plumes were deflected around the Shelburne Plateau, which lies between Lake Huron and Lake Ontario. Future research will focus on interactions between circulations downwind of Lake Huron and snowbands that form over Lake Ontario.

The results of the 4–5 January 1995 simulation are sufficiently encouraging to suggest that MM5 may be used to make real-time forecasts of lake-effect snowstorms. The lead author is participating in a COMET cooperative project to provide lake-effect snow forecasts, in GEMPAK format, to the National Weather Service Forecast Offices at Buffalo and Binghamton using a 20-km nested grid over Lakes Huron, Erie, and Ontario. Despite relatively coarse resolution, MM5 has produced useful predictions of snowband location and movement during the 1996/97 and 1997/98 lake-effect snow seasons.

Full access