Search Results

You are looking at 1 - 2 of 2 items for :

  • Author or Editor: R. M. Johnson x
  • Weather and Forecasting x
  • Refine by Access: All Content x
Clear All Modify Search
Matthew J. Bunkers, Jeffrey S. Johnson, Lee J. Czepyha, Jason M. Grzywacz, Brian A. Klimowski, and Mark R. Hjelmfelt

Abstract

The local and larger-scale environments of 184 long-lived supercell events (containing one or more supercells with lifetimes ≥4 h; see Part I of this paper) are investigated and subsequently compared with those from 137 moderate-lived events (average supercell lifetime 2–4 h) and 119 short-lived events (average supercell lifetime ≤2 h) to better anticipate supercell longevity in the operational setting. Consistent with many previous studies, long-lived supercells occur in environments with much stronger 0–8-km bulk wind shear than what is observed for short-lived supercells; this strong shear leads to significant storm-relative winds in the mid- to upper levels for the longest-lived supercells. Additionally, the bulk Richardson number falls into a relatively narrow range for the longest-lived supercells—ranging mostly from 5 to 45. The mesoscale to synoptic-scale environment can also predispose a supercell to be long or short lived, somewhat independent of the local environment. For example, long-lived supercells may occur when supercells travel within a broad warm sector or else in close proximity to mesoscale or larger-scale boundaries (e.g., along or near a warm front, an old outflow boundary, or a moisture/buoyancy axis), even if the deep-layer shear is suboptimal. By way of contrast, strong atmospheric forcing can result in linear convection (and thus shorter-lived supercells) in a strongly sheared environment that would otherwise favor discrete, long-lived supercells.

Full access
L.W. Larson, R.L. Ferral, E.T. Strem, A.J. Morin, B. Armstrong, T.R. Carroll, M.D. Hudlow, L.A. Wenzel, G.L. Schaefer, and D.E. Johnson

Abstract

The River and Flood Program in the National Weather Service, in its mission to save lives and property, has the responsibility to gather hydrologic data from a variety of sources and to assemble the data to make timely and reliable hydrologic forecasts. The intent of this paper, the second in a series of three, is to present an overview of the operational responsibilities of the River and Flood Program: how data are collected, what models-systems are currently in operation to process the data, and how the application of these procedures and techniques are applied in different types of hydrologic forecasting.

Full access