The lake-effect rain showers of September 2, 2008

What happened

On September 2, 2008, a narrow band of lake-effect rain showers set up and gave some precipitation to western portions of Winnipeg. The synoptic setup was just right, with 850 mb temperatures of about 3°C and lake temperatures around 18°C, exceeding the minimum threshold of a temperature difference of 13°C typically regarded as the minimum required to produce lake-effect precipitation.

Note how around 0000Z, the velocity animation shows lower speeds within the core of the heaviest rain--this is likely because of precipitation drag acting on the inner part of the precipitation band.

When we talk about precipitation drag, we usually are referring to precipitation in a convective event (usually a thunderstorm) falling through high winds aloft, transporting that momentum down to the surface. However, in this case, we are referring to precipitation drag in that the precipitation is heavier than the smaller particles being sensed by the RADAR, and thus moving a bit more slowly. This is likely what happens in thunderstorms anyway, but usually the wind speeds involved are higher, so the difference is much less and thus harder to notice.

RADAR images

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Last update to this page: September 3, 2008