WELCOME BACK: Procedure continued from STUDY GUIDE.
The Monday, 30 October 2000, Daily Weather Summary describes three storm systems that affected the weather across the coterminous US over the past weekend. One storm swept up the East Coast bringing rain and snow to New England. A second created severe weather in the south central US. A pair of storms came ashore along the West Coast. It seems as though the "weather goblins" were active almost everywhere. Image 1 is the surface weather map (Isobars, Fronts, Radar, & Data) for 12Z, Sunday, 29 OCT 2000, showing the locations of the low pressure centers and associated fronts over the lower 48 states. The New England storm was centered just off the map with its precipitation and isobar patterns marking its western edge.
The circulation patterns of winds about the western side of the New England low pressure center and also about the Low along the Colorado/Kansas border were generally [(clockwise and outward) (counterclockwise and inward)]. These patterns [(are) (are not)] consistent with that of the hand-twist model of a Low used earlier in Activity 1B. (The low-pressure areas across the West exhibit low speed flow patterns that are dominated by the mountainous terrain.)
The circulation pattern of winds in the Great Lakes and surrounding states in the high pressure area, centered to the north in eastern Canada just off the map area, was generally [(clockwise and outward) (counterclockwise and inward)]. This pattern [(is) (is not)] consistent with that of the hand-twist model of a High
Rapid City, South Dakota, has coded pressure digits of "071". This is decoded to a sea-level pressure of _________ mb. Green Bay, Wisconsin, has coded pressure digits of "329". This is decoded to a sea-level pressure of _________ mb. The pressure difference over this distance is __________ mb.
The horizontal pressure gradient force is the dominant force in bringing about large-scale horizontal air motions. The strength of the pressure gradient force, the pressure difference over distance, is shown by the isobar patterns. Between Rapid City and Green Bay, there are [(1) (4) (7)] isobar lines plotted. By comparison, there are few isobars in the comparable distance between Lake Charles, Louisiana, and Charleston, South Carolina, where the pressure difference was 2.8 mb.
In general, the stronger pressure gradient, as shown by the number of isobars across a given distance, was located in the [(Northern Plains) (Southeast)] area at map time. Wind speeds across the Southeast are from calm to about 10 knots. Several stations in Minnesota, South Dakota and North Dakota show wind speeds of 15 knots. Bismarck, ND, had 20 kts.
Based on the isobar pattern, the area of strongest pressure gradient on this map is [(New England) (Arizona)]. The higher wind speeds reported over the weekend across New England were associated with strong pressure gradients, where the isobars are most closely spaced.
Amarillo, the northern-most station in Texas, reported a wind direction from the [(southwest) (northwest)]. The orientation of the isobar at Amarillo indicates lower pressure was generally in the direction towards the [(south) (north)]. The horizontal pressure gradient force acting on the air at Amarillo was directed generally toward the center of low pressure, and [(perpendicular) (parallel)] to the isobars.
Albany, New York, where it was 32 °F and overcast under the influence of the New England Low, had a wind direction from the [(southwest) (northwest)]. The horizontal pressure gradient force acting on the air at Albany was directed [(perpendicular) (parallel)] to the isobars, generally towards [(lowest) (highest)] pressure.
In the Northern Hemisphere, moving air also experiences a Coriolis force that is directed to the [(right) (left)] of the direction of motion. Consequently, the Coriolis force acting on the wind at Amarillo would be directed toward the [(southeast) (northwest)]. The Coriolis force acting on the wind at Albany would be directed toward the [(right) (left)] of the wind direction, to the southwest.
A third force acting on air moving near the Earth's surface is friction. Friction, which always acts in the direction opposite to motion, retards the movement of the air. The direction of the frictional force on the air at Amarillo was towards the [(southwest) (northwest)]. The frictional force acting on air at Albany was toward the [(southwest) (northwest)]
This frictional force, having slowed the air and reduced the Coriolis force, brings about the flow of air along a path cutting across the isobars towards lower pressure. In this way, air spirals into lows and out of highs as shown with the WeatherCycler and the hand-twist model.
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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