February 20, 2018

Freezing Rain

Current Conditions

Temperature: 17 degrees, feels like 8 degrees
Dew Point: 11 degrees
Winds: W 8 mph
Pressure: 1023.0 mb
Visibility: 10 mph

This morning the temperature was 21 degrees with N 4 mph winds. The dew point was 19 degrees indicating a high moisture content in the air. Early this morning there was a remnant of the freezing rains the Eau Claire area received yesterday but the rain mostly stopped by 8:00 AM. Over the course of the day the sky stayed over cast and the high temperature was 22 degrees. Light fog was present in the early afternoon. Currently the temperature is dropping and winds have shifted to the west.

The current surface map shows a great example of a mid-latitude cyclone. Mid-latitude cyclones are characterized by a series of low pressure systems moving together. This has created a trough spanning the entire United States! In figure 1 a surface map shows the line of precipitation that is following the low pressure trough.

Figure 1. Surface map of the United States with precipitation events.

This precipitation is a result of the cooler air from the continental polar air mass colliding with the warm air following the jet stream to the south (figure 2).

Figure 2. Jet stream coming off the southern Pacific Ocean and carrying moist air into the Midwest.

The air carried by the jet stream has a large amount of water vapor indicated in figure 3.

Figure 3. Water vapor following the pattern of the jet stream. The water vapor is responsible for the precipitation along the low pressure systems.

Yesterday I predicted that the temperature would be about the same and it was. The wintry mix was still present but not as much as I was expecting.

Tomorrow I predict that temperatures will be cooler due to the high pressure air mass moving into the area shown in figure 1. The low pressure systems are moving south which means no precipitation for the time being.