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Earth and Atmospheric Sciences Department | |
 Current conditions courtesy of aprweather.com |
Saint Cloud Forecasts | |
Manufacturing Cold Air
Mixed Precipitation of 28-January-2005
How do you manufacture enough cold air to produce snow? On 28-Jan-2005 at 1245Z, the surface temperatures were below freezing, but there was a mixture of snow, freezing rain (sideways S), and sleet (misused double arrow) in western and central Minnesota. The 12Z 28-Jan-2005 850 mb analysis shows little or no temperature advection over the Northern Plains. More importantly, temperatures are near or above freezing at Chanhassen, Valley, and Aberdeen, making melting at the base of the cloud more likely.
The 12Z sounding from Chanhassen shows this warm layer between 840 and 880 mb. This would be sufficient to melt falling snowflakes. The deep cold subcloud layer would allow precipitation to refreeze as sleet. So, how can the cold layer be recovered? Two ways.
- Evaporational Cooling
- Dynamic Cooling
