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.ppt ( قابل ویرایش و آماده پرینت )
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قسمتی از متن .ppt :
Snow to Liquid Ratio: Climatology and Forecast Methodologies
LSX WFO Winter Weather Workshop
7 November 2005
Martin A. Baxter
Cooperative Institute for Precipitation Systems
Saint Louis University
Dept. of Earth and Atmospheric Sciences
Forecasting Winter Precipitation is a Two-Step Process
First, the current dynamic and thermodynamic forcings of the storm must be assessed.
Numerical model forecasts must be studied, especially the model quantitative precipitation forecast (QPF).
Second, the evolution of the hydrometeors from their origin to the surface must be predicted.
This evolution will be determined by the vertical profile of temperature and moisture.
This profile will elucidate the type of precipitation- rain, snow, freezing rain, ice pellets, or any combination.
If the precipitation is expected to fall as snow, a snow to liquid equivalent ratio must be determined to forecast the actual snow amount.
Why is liquid ratio important to forecasters?
After forecasting liquid equivalent (QPF), the snow-liquid equivalent ratio must be estimated.
Significant variations in snow to liquid equivalent ratio can occur even within a single storm system
A more clear understanding of the processes that act to vary snow density will enable the forecaster to employ a more scientific process oriented method toward forecasting snowfall, versus commonly used empirical techniques.
A challenge exists to determine the extent of interaction between the dynamical forcing and the microphysical processes that determine snow density (i.e., how efficient is the forcing in producing snowfall from a given amount of liquid equivalent?).
SLR determines the wintertime precipitation efficiency
NWS “New Snowfall to Estimated Meltwater Conversion Table” (Kyle and Wesley 1996)
Utilizes surface temperatures to estimate snowfall from liquid equivalent
Is only marginally effective, as it does not account for geographic location or in-cloud microphysical processes.
