4. Forecast Applications

Winter Weather » Precipitation Type 1200 UTC Day 1 (Hour 12)

Hypothetical sounding for precipitation type forecasting exercise, step 2

The latest sounding is saturated throughout the lower and middle troposphere with the temperatures and dewpoints generally corresponding to the wet-bulb temperatures in the sounding 12 hours ago. Precipitation began falling about 2 hours ago, initially as light rain, but quickly turned to snow as evaporative cooling lowered the temperatures to 0°C or below in the boundary layer as it saturated. Moderate snow is being observed at the surface, and it is beginning to accumulate on grassy surfaces. The NWP models are consistent in predicting warm advection aloft in a narrow layer centered around 800 hPa. The forecast indicates the 800 hPa temperature will warm approximately 2°C during the next twelve hours (by 0000 UTC Day 2), but temperatures below 850 hPa will remain fairly steady through the period.