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Precip Type Forecasting – The Top Down Method

Precip Type Forecasting – The Top Down Method. Top down approach uses soundings to forecast precip type. Four Steps: 1. Is there ice in the cloud? 2. Consider dry layers. 3. Consider warm layers. 4. Consider near surface conditions. Is There Ice in the Cloud?. Start at top of sounding

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Precip Type Forecasting – The Top Down Method

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  1. Precip Type Forecasting – The Top Down Method

  2. Top down approach uses soundings to forecast precip type. • Four Steps: • 1. Is there ice in the cloud? • 2. Consider dry layers. • 3. Consider warm layers. • 4. Consider near surface conditions.

  3. Is There Ice in the Cloud? • Start at top of sounding • Find first cloud layer • Determine temperature at this cloud layer • Coldest temperature

  4. Cloud layer

  5. Cloud Layer

  6. Consider the Dry Layers • Will the precip particle evaporate? • Will temperature cool to the wet bulb temperature? • If so, the layer will become saturated. • Is there a seeder feeder situation? • 2 cloud layers, one with ice • Ice does not evaporate and falls into lower cloud • Whole cloud layer eventually contains ice

  7. Seeder Feeder

  8. Evaporates

  9. Dry Layer Probably does not evaporate

  10. Consider the Warm Layers • If there is no warm layer, ice continues to fall • If there is, must determine if ice will melt • Keep wet bulb temp in mind • Layer will cool if precip is falling • If ice is falling:

  11. Warm Layer Ice completely melts

  12. Warm layer Ice does not melt

  13. Lastly, Look Near the Surface • Does precip re-freeze, continue to melt, freeze on contact, etc. If ice is falling: If mix is falling:

  14. If super cooled water is falling: Basically, look at depth and temp of near surface cold layer and surface wet bulb temperature. There are always exceptions!

  15. Example freezing rain sounding

  16. Example snow sounding

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