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Mid-Latitude Cyclone Practice
Below is a description of the major weather features at 12Z on December 12, 1999. This is the type of discussion I would expect in your assignment. Below is the 300 mb map for 12Z on December 12, 1999. There is a trough over the central plains region, from the western Texas up through the Dakotas. The east coast is dominated by a an upper level ridge. The peak wind speed (175 kts) is over Greenbay WI. Using the applet below we can see that the trough is moving to the east. You can see this in the movement of the trough and the shift in wind direction over the Mississippi Valley. At 12Z on December 12, 1999 (see map below) a midlatitude cyclone is developing over East Texas and Louisiana. Most of the precipitation, as indiciated by the radar and the surface observations, show the precipitation to be ahead of the warm front. This is to the east of the upper level trough. Large areas of fog are observed throught the central plains, behind the midlatitude cyclone. This is likely a result of a moist surface and radiational cooling at night.
The East Coast is dominated by high pressure at the surface, as expected from the upper air pattern. The skies are clear from most of the upper Mid-west and Western states. A mid-latitude cyclone is once again moving into the Northwest. An arctic airmass appears in Canada, just off the map.
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The upper air sounding over Little Rock AR for 12Z on Dec 12 and 0Z on Dec 13 indicates that the mid-layers of the atmosphere, between about 700 and 300mb are 'drying out', that is the difference between the temperature and dewpoint temperature are increasing. the tropopause is located at approximately 175 mb. The upper levels of the troposphere appear to be moistening, indicating that cirrus clouds may be present. If the upper level trough continues to move eastward, it is likely that the clouds over Little Rock will clear out as the mid-latitude cyclone progresses eastward.