An Interactive Method for Estimating Maximum Hailstone Size from Forecast Soundings

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  • 1 Saint Louis University, Department of Earth and Atmospheric Sciences, St. Louis, Missouri
  • | 2 U.S. Air Force, 30th Weather Squadron/DON, APO San Francisco, California
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Abstract

A diagnostic/prognostic sounding analysis package is presented to aid operational forecasters. First, a diagnostic sounding analysis is shown which computes standard thermodynamic parameters while including a scheme to estimate the maximum hail diameter based on the positive areas above the convective condensation level (CCL) and the level of free convection (LFC). The hail algorithm basically uses the Anthes’ one-dimensional cloud model to estimate vertical motion which then is used to compute the hail diameter. A melting scheme is also presented to account for the inciting of hailstones in deep, warm wet-bulb temperature layers. Compared to the traditional Fawbush-Miller approach, the Pino-Moore hail algorithm showed improvement, significant at the 0.5% level when tested during actual hail events.

A forecast-sounding algorithm based on a technique described by McGinley is used to modify the morning sounding to account for insulation. For soundings without inversions mixing is also permitted to change the boundary layer dew point profile in accordance with results provided by Schaefer. Above the boundary layer a small percentage of the geostrophic thermal advection is used to estimate changes in the temperature aloft. Interaction with the forecaster is emphasized during each step of the forecast-sounding algorithm. The forecast sounding can then be used in the stability analysis program to generate a more realistic afternoon sounding with which to estimate the maximum hail diameter.

Abstract

A diagnostic/prognostic sounding analysis package is presented to aid operational forecasters. First, a diagnostic sounding analysis is shown which computes standard thermodynamic parameters while including a scheme to estimate the maximum hail diameter based on the positive areas above the convective condensation level (CCL) and the level of free convection (LFC). The hail algorithm basically uses the Anthes’ one-dimensional cloud model to estimate vertical motion which then is used to compute the hail diameter. A melting scheme is also presented to account for the inciting of hailstones in deep, warm wet-bulb temperature layers. Compared to the traditional Fawbush-Miller approach, the Pino-Moore hail algorithm showed improvement, significant at the 0.5% level when tested during actual hail events.

A forecast-sounding algorithm based on a technique described by McGinley is used to modify the morning sounding to account for insulation. For soundings without inversions mixing is also permitted to change the boundary layer dew point profile in accordance with results provided by Schaefer. Above the boundary layer a small percentage of the geostrophic thermal advection is used to estimate changes in the temperature aloft. Interaction with the forecaster is emphasized during each step of the forecast-sounding algorithm. The forecast sounding can then be used in the stability analysis program to generate a more realistic afternoon sounding with which to estimate the maximum hail diameter.

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