WELCOME BACK: Procedure continued from STUDY GUIDE.
Over the past weekend, two low-pressure systems and a complex of associated fronts brought precipitation to the central US. Persistent thunderstorms in Texas brought flooding rains to that area. There were also reports of tornadoes and wind damage. The counterclockwise circulation around the north side of the southern Low produced upslope flow that brought snow to the Denver area. These conditions are detailed in the Monday, 6 November 2000, Daily Weather Summary.
Image 1 is the 500-mb constant-pressure map for 00Z 06 NOV 2000. The 06 NOV 2000 500-mb map of conditions in the middle troposphere had a contour pattern that showed a [(trough) (ridge)] over the western half of the country. There was a [(trough) (ridge)] over the eastern half. Also, the contour pattern in New England suggests a closed circulation around lower heights.
The wind speeds reported on the 06 NOV 2000 500-mb map are generally faster where the contour lines are relatively [(far apart) (close together)]. And where the wind speeds are greater than about 25 knots, the wind directions are generally [("parallel") (perpendicular)] to the contour lines.
Image 2 is the 300-mb constant-pressure map for 00Z 06 NOV 2000, the same time as the 500-mb map of Image 1. This level represents conditions in the upper troposphere. The plotted heights are in 10's of meters. The heights at which 300 mb of pressure occurred over the US at map time were within several hundred meters of [(5500) (9000) (12,500)] meters.
Compare the heights of the 300-mb pressures at stations across the US. In general, the heights of the 300-mb pressure level were [(higher) (lower)] across the northern tier of states than heights in the Gulf Coast region. Stations across the northern US were also reporting temperatures at this pressure level that were [(warmer) (cooler)] than those of the Gulf Coast area.
Compare the flow patterns of the air at the 500-mb and 300-mb pressure levels. The location of troughs and ridges at the two levels are in [(similar) (opposite)] parts of the country.
Comparing the two 00Z 06 NOV 2000 maps, the wind speeds generally [(increase) (remain the same) (decrease)] with increasing height above the Earth's surface.
Using the conventional threshold of 70 knots wind speed for the existence of a jet stream, there [(is) (is not)] evidence for a jet stream on the 300-mb constant-pressure map. One band of high wind speeds at 300 mb, some 100 knots or higher, exists from Washington State to [(Arizona) (North Dakota)]. Another higher wind speed region is found from north central Texas to Iowa.
Commercial aircraft routinely fly at heights near the 300-mb level. If one were to be flying from Midland, in west-central Texas across eastern Kansas to Chicago, Illinois about 00Z on 06 NOV 2000 at the 300-mb level, the aircraft's speed relative to the ground ("ground speed") would be around 90 knots [(faster) (slower)] than its speed relative to the air through which it is moving ("air speed").
The dashed lines are isotachs that encircle regions of particular wind speeds. For example, a 90-knot isotach from northern Oklahoma to southwestern Iowa shows a "jet streak" or locally faster region of wind speeds within the general flow. Winds at 300 mb speeding up as they enter this region helped support the rising motions associated with the severe weather across the Southern Plains at this time.
Hold this activity until you have completed all applications for this week.
Instructions for faxing your LIT mentor will appear at the end of this week's
Activity B.
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