JP7.3
A new product to help forecast convective initiation in the 1-6 hour timeframe
John R. Walker, University of Alabama, Huntsville, AL; and J. R. Mecikalski and W. M. MacKenzie
Forecasting convection initiation (CI) has been a difficult problem in the Atmospheric Sciences today. There are several means (via radar and satellite) which can attempt to nowcast CI within the 0-1 hour timeframe. Forecasting CI within the 1-6 hour timeframe remains difficult, due to the frequent inability of numerical weather prediction models to “spin up” the important gradients in a timely fashion, and because simple time extrapolation fail beyond ~2 hours when attempting to predict convective initiation.
We will present a new product that will help with the forecasting of air mass thunderstorms in the 1-6 hour time-frame by identifying potential sources of updrafts near differential heating boundaries. The product will be easily generated daily, and in a very timely fashion, so that it could be used as a tool by operational forecasters to assess regions of preferred CI each day.
The hypothesis that is being tested via this product is that under synoptically “calm” conditions, when surface winds are generally <5 m/s and baroclinicity is weak, thermal circulations will form along differential heating gradients, similar to “inland sea-breezes”. In the past, these thermals have been termed “Nonclassical Mesoscale Circulations”, or simply, NCMCs (Segal and Arritt, 1992). Given enough atmospheric instability, the location of these circulations will act as source regions for updrafts and, eventually, deep convection. Data sets of remotely-sensed vegetation from MODIS Level 3, 16-day composites, recent rainfall estimates observed from radar and NOAA/NWS, and GOES-derived insolation are used to create differential heating indicies that will help identify these source regions.
Joint Poster Session 7, Natural Hazards
Wednesday, 14 January 2009, 2:30 PM-4:00 PM, Hall 5
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