Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: R. A. Brown x
  • Weather and Forecasting x
  • Refine by Access: All Content x
Clear All Modify Search
Rodger A. Brown, Thomas A. Niziol, Norman R. Donaldson, Paul I. Joe, and Vincent T. Wood

Abstract

During the winter, lake-effect snowstorms that form over Lake Ontario represent a significant weather hazard for the populace around the lake. These storms, which typically are only 2 km deep, frequently can produce narrow swaths (20–50 km wide) of heavy snowfall (2–5 cm h−1 or more) that extend 50–75 km inland over populated areas. Subtle changes in the low-altitude flow direction can mean the difference between accumulations that last for 1–2 h and accumulations that last 24 h or more at a given location. Therefore, it is vital that radars surrounding the lake are able to detect the presence and strength of these shallow storms. Starting in 2002, the Canadian operational radars on the northern side of the lake at King City, Ontario, and Franktown, Ontario, began using elevation angles of as low as −0.1° and 0.0°, respectively, during the winter to more accurately estimate snowfall rates at the surface. Meanwhile, Weather Surveillance Radars-1988 Doppler in New York State on the southern and eastern sides of the lake—Buffalo (KBUF), Binghamton (KBGM), and Montague (KTYX)—all operate at 0.5° and above. KTYX is located on a plateau that overlooks the lake from the east at a height of 0.5 km. With its upward-pointing radar beams, KTYX’s detection of shallow lake-effect snowstorms is limited to the eastern quarter of the lake and surrounding terrain. The purpose of this paper is to show—through simulations—the dramatic increase in snowstorm coverage that would be possible if KTYX were able to scan downward toward the lake’s surface. Furthermore, if KBUF and KBGM were to scan as low as 0.2°, detection of at least the upper portions of lake-effect storms over Lake Ontario and all of the surrounding land area by the five radars would be complete. Overlake coverage in the lower half (0–1 km) of the typical lake-effect snowstorm would increase from about 40% to about 85%, resulting in better estimates of snowfall rates in landfalling snowbands over a much broader area.

Full access
Rodger A. Brown, Vincent T. Wood, Randy M. Steadham, Robert R. Lee, Bradley A. Flickinger, and Dale Sirmans

Abstract

For the first time since the installation of the national network of Weather Surveillance Radar-1988 Doppler (WSR-88D), a new scanning strategy—Volume Coverage Pattern 12 (VCP 12)—has been added to the suite of scanning strategies. VCP 12 is a faster version of VCP 11 and has denser vertical sampling at lower elevation angles. This note discusses results of field tests in Oklahoma and Mississippi during 2001–03 that led to the decision to implement VCP 12. Output from meteorological algorithms for a test-bed radar using an experimental VCP were compared with output for a nearby operational WSR-88D using VCP 11 or 21. These comparisons were made for severe storms that were at comparable distances from both radars. Findings indicate that denser vertical sampling at lower elevation angles leads to earlier and longer algorithm identifications of storm cells and mesocyclones, especially those more distant from a radar.

Full access
Mark DeMaria, John A. Knaff, Michael J. Brennan, Daniel Brown, Richard D. Knabb, Robert T. DeMaria, Andrea Schumacher, Christopher A. Lauer, David P. Roberts, Charles R. Sampson, Pablo Santos, David Sharp, and Katherine A. Winters

Abstract

The National Hurricane Center Hurricane Probability Program, which estimated the probability of a tropical cyclone passing within a specific distance of a selected set of coastal stations, was replaced by the more general Tropical Cyclone Surface Wind Speed Probabilities in 2006. A Monte Carlo (MC) method is used to estimate the probabilities of 34-, 50-, and 64-kt (1 kt = 0.51 m s−1) winds at multiple time periods through 120 h. Versions of the MC model are available for the Atlantic, the combined eastern and central North Pacific, and the western North Pacific. This paper presents a verification of the operational runs of the MC model for the period 2008–11 and describes model improvements since 2007. The most significant change occurred in 2010 with the inclusion of a method to take into account the uncertainty of the track forecasts on a case-by-case basis, which is estimated from the spread of a dynamical model ensemble and other parameters. The previous version represented the track uncertainty from the error distributions from the previous 5 yr of forecasts from the operational centers, with no case-to-case variability. Results show the MC model provides robust estimates of the wind speed probabilities using a number of standard verification metrics, and that the inclusion of the case-by-case measure of track uncertainty improved the probability estimates. Beginning in 2008, an older operational wind speed probability table product was modified to include information from the MC model. This development and a verification of the new version of the table are described.

Full access