Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: Brian Motta x
  • Refine by Access: All Content x
Clear All Modify Search
Dan Bikos, John Weaver, and Brian Motta

Abstract

Geostationary Operational Environmental Satellite (GOES) imagery from 3 May 1999 is examined. Synoptic-scale water vapor imagery shows a deepening low-amplitude upper-level trough over the western United States on 3 May, which develops a negative tilt as a jet streak digs south-southeastward over California. The imagery also shows a second jet streak propagating rapidly from Baja California to the southern Great Plains. This feature intensifies as it propagates into the diffluent region on the east side of the trough. Thunderstorms initiate as this jet streak moves over western Oklahoma during the late afternoon. GOES visible imagery shows a north–south cloud boundary over southwestern Oklahoma on 3 May. To the west of this boundary, cumulus cloudiness dominates. To the east, stratocumulus and wave (billow) clouds characterize the low-level cloud field. As the jet streak and associated cirrus propagate over northern Texas, towering cumulus clouds develop and then dissipate. As the cirrus clouds propagate over western Oklahoma, towering cumulus clouds develop and persist. This note discusses important features observed in GOES imagery as it pertains to convective morphology. These features were not adequately resolved by the numerical models but were important in the forecast. The benefits of using satellite imagery in combination with model output and other data are discussed.

Full access
Evan A. Kalina, Katja Friedrich, Brian C. Motta, Wiebke Deierling, Geoffrey T. Stano, and Nezette N. Rydell

Abstract

Synoptic weather, S-band dual-polarization radar, and total lightning observations are analyzed from four thunderstorms that produced “plowable” hail accumulations of 15–60 cm in localized areas of the Colorado Front Range. Results indicate that moist, relatively slow (5–15 m s−1) southwesterly-to-westerly flow at 500 hPa and postfrontal low-level upslope flow, with 2-m dewpoint temperatures of 11°–19°C at 1200 LST, were present on each plowable hail day. This pattern resulted in column-integrated precipitable water values that were 132%–184% of the monthly means and freezing-level heights that were 100–700 m higher than average. Radar data indicate that between one and three maxima in reflectivity Z (68–75 dBZ) and 50-dBZ echo-top height (11–15 km MSL) occurred over the lifetime of each hailstorm. These maxima, which imply an enhancement in updraft strength, resulted in increased graupel and hail production and accumulating hail at the surface within 30 min of the highest echo tops. The hail core had Z ~ 70 dBZ, differential reflectivity Z DR from 0 to −4 dB, and correlation coefficient ρ HV of 0.80–0.95. Time–height plots reveal that these minima in Z DR and ρ HV gradually descended to the surface after originating at heights of 6–10 km MSL ~15–60 min prior to accumulating hailfall. Hail accumulations estimated from the radar data pinpoint the times and locations of plowable hail, with depths greater than 5 cm collocated with the plowable hail reports. Three of the four hail events were accompanied by lightning flash rates near the maximum observed thus far within the thunderstorm.

Full access
Zoltan Toth, Mark Tew, Daniel Birkenheuer, Steve Albers, Yuanfu Xie, and Brian Motta
Full access
Katja Friedrich, Robinson Wallace, Bernard Meier, Nezette Rydell, Wiebke Deierling, Evan Kalina, Brian Motta, Paul Schlatter, Thomas Schlatter, and Nolan Doesken

Abstract

In recent years, hail accumulations from thunderstorms have occurred frequently enough to catch the attention of the National Weather Service, the general public, and news agencies. Despite the extreme nature of these thunderstorms, no mechanism is currently in place to obtain adequate reports, measurements, or forecasts of accumulated hail depth. To better identify and forecast hail accumulations, the Colorado Hail Accumulation from Thunderstorms (CHAT) project was initiated in 2016 with the goals of collecting improved and more frequent hail depth reports on the ground as well as studying characteristics of storms that produce hail accumulations in Colorado. A desired outcome of this research is to identify predictors for hail-producing thunderstorms typically occurring along the Colorado Front Range that might be used as operational nowcast products in the future. During the 2016 convective season, we asked amateur meteorologists to send general information, photos, and videos on hail depth using social media. They submitted over 58 reports in Colorado with information on location, time, depth, and areal coverage of hail accumulations. We have analyzed dual-polarization radar and lightning mapping array data from 32 thunderstorms in Colorado, which produced between 0.5 and 50 cm of hail accumulation on the ground, to identify characteristics unique to storms with hail accumulations. This preliminary analysis shows how enhanced in-cloud hail presence and surface accumulation can be tracked throughout the lifetime of a thunderstorm using dual-polarization radar and lightning data, and how hail accumulation events are associated with large in-cloud ice water content, long hailfall duration, or a combination of these.

Open access
Adrian A. Ritchie Jr., Matthew R. Smith, H. Michael Goodman, Ronald L. Schudalla, Dawn K. Conway, Frank J. LaFontaine, Don Moss, and Brian Motta

Abstract

Antenna temperatures and the corresponding geolocation data from the five sources of the Special Sensor Microwave/Imager data from the Defense Meteorological Satellite Program F11 satellite have been characterized. Data from the Fleet Numerical Meteorology and Oceanography Center (FNMOC) have been compared with data from other sources to define and document the differences resulting from different processing systems. While all sources used similar methods to calculate antenna temperatures, different calibration averaging techniques and other processing methods yielded temperature differences. Analyses of the geolocation data identified perturbations in the FNMOC and National Environmental Satellite, Data and Information Service data. The effects of the temperature differences were examined by generating rain rates using the Goddard Scattering Algorithm. Differences in the geophysical precipitation products are directly attributable to antenna temperature differences.

Full access
Neil A. Stuart, Patrick S. Market, Bruce Telfeyan, Gary M. Lackmann, Kenneth Carey, Harold E. Brooks, Daniel Nietfeld, Brian C. Motta, and Ken Reeves
Full access
Hongli Jiang, Steve Albers, Yuanfu Xie, Zoltan Toth, Isidora Jankov, Michael Scotten, Joseph Picca, Greg Stumpf, Darrel Kingfield, Daniel Birkenheuer, and Brian Motta

Abstract

The accurate and timely depiction of the state of the atmosphere on multiple scales is critical to enhance forecaster situational awareness and to initialize very short-range numerical forecasts in support of nowcasting activities. The Local Analysis and Prediction System (LAPS) of the Earth System Research Laboratory (ESRL)/Global Systems Division (GSD) is a numerical data assimilation and forecast system designed to serve such very finescale applications. LAPS is used operationally by more than 20 national and international agencies, including the NWS, where it has been operational in the Advanced Weather Interactive Processing System (AWIPS) since 1995.

Using computationally efficient and scientifically advanced methods such as a multigrid technique that adds observational information on progressively finer scales in successive iterations, GSD recently introduced a new, variational version of LAPS (vLAPS). Surface and 3D analyses generated by vLAPS were tested in the Hazardous Weather Testbed (HWT) to gauge their utility in both situational awareness and nowcasting applications. On a number of occasions, forecasters found that the vLAPS analyses and ensuing very short-range forecasts provided useful guidance for the development of severe weather events, including tornadic storms, while in some other cases the guidance was less sufficient.

Full access