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SURFACE AIR PRESSURE PATTERNS |
Note: This Activity is the same as AMS Weather Studies Current Weather Studies 1A from Preview Week. Students only need to complete the Activity once.
Welcome to the preview week of AMS Weather Studies. We hope the use of current weather information will become a pleasant and anticipated daily experience. We encourage your exploration of the online weather products from the website.
Image 1 ("Pressures" map) was acquired from the course website and reports surface air pressures (corrected to sea level) rounded to the nearest whole millibar at 00Z 30 AUG 2009, actually 8 PM EDT (7 PM CDT, 6 PM MDT, 5 PM PDT, etc.) on Sunday evening.
The lowest plotted air pressure on the map is [(1003)(1006)(1009)] mb at several stations in New York and central Pennsylvania.
The highest reported pressure is 1023 mb in [(Williston, ND)(Seattle, WA)].
The isobars in the conventional series that will be needed to complete the pressure analysis between the lowest and highest values on this map are: [(1006, 1010, 1014, 1018)(1007, 1011, 1015, 1019)(1008, 1012, 1016, 1020)].
An isobar is not needed when a pressure value the same as that of the isobar occurs at a single point and there are no pressures less/greater than its value reported nearby. More than one isobar of the same value may need to be drawn if pressure values located in separate sections of the map area require it. Two isobars have already been drawn in southern Canada where values not reported on the map indicated the extremes of the pressure pattern across the northern portion of the map region.
Using a pencil, follow the steps below to complete the pressure analysis to determine the pressure pattern that existed at the time the observations were made. Consider each pressure value to be located at the center of the reported number.
Arbitrarily we might start by drawing the 1008-mb isobar, the first of the series. This isobar may be started by going through the "1008" located in northern Michigan southeastward to another 1008 in Virginia. Label this isobar with its value, 1008, at the ends of the isobar line where it enters or leaves the map field. Another portion of a 1008-mb isobar will cross New Hampshire and southern Maine. The pressure values across the Northeast between those 1008-mb isobars including the 1004-mb isobar in southeastern Ontario Canada are [(less than)(equal to)(greater than)] 1008 mb.
Continue drawing and labeling isobars of the series where they existed within the data pattern. Note that several of the isobar values appear in both the northeastern U.S. and the western U.S. Label your isobars with their values at the ends that extend just beyond the data field.
Image 2 is the analyzed surface pressure map from the National Oceanic and Atmospheric Administration's (NOAA) National Centers for Environmental Prediction (NCEP) for 00Z 30 AUG 2009. The Image 2 map shows the location of air pressure system centers and fronts. The Image 2 map [(is)(is not)] the same time and date as the Image 1 map of pressures you have just analyzed.
Compare your isobar pattern with that drawn on the Image 2 map. The Image 2 map is constructed by computer based on a much more complete set of pressure values. (This may account for some of the variations between your analysis and that by the computers. It also is the source of several of the plotted Hs and Ls denoting locally minimally higher or lower pressure centers, respectively.) The L located in the Atlantic Ocean off Delaware denotes the location of the tropical depression named Danny at that time.
The bold red and blue lines are fronts that are generally associated with the Lows (L). Dashed orange lines are troughs or extensions of lower pressure often acting like fronts. Light blue, green and yellow shadings scattered across the map are areas where radar beams were reflected back to the radar sites indicating varying intensities of precipitation (see scale to the left margin). Generally, the radar-indicated precipitation areas [(are)(are not)] associated with the Ls and frontal positions.
By analyzing the pressure values reported on weather maps to find pressure patterns, one can locate the centers of locally highest and lowest pressures, respectively. We will see that these pressure centers often mark the midpoints of major weathermakers.
Suggestions for further activities: The AMS Weather Studies website routinely delivers unanalyzed ("Pressures") and analyzed ("Isobars & Pressures") surface pressure maps. Practice drawing isobars by calling up the unanalyzed version. Note: If you would like to practice more on drawing isopleths (lines of a constant value) in groups of numbers, from simple to more complex patterns, go to: http://profhorn.aos.wisc.edu/wxwise/AckermanKnox/chap1/Contour_page1.html.
Common NWS terminology for regions of the country which may be useful is at: http://www.hpc.ncep.noaa.gov/images/us_bndrys1_print.gif and http://www.hpc.ncep.noaa.gov/images/us_bndrys2_print.gif.
Critical Thinking and Diversity Component: AMS Weather Studies is particularly suited to modeling critical thinking. In each Week's "A" Current Weather Studies we will alert you to the week's Critical Thinking and Diversity Component, which is located in the Learning Files section of the course homepage under Critical Thinking/Diversity. The Week 1 Critical Thinking/Diversity Component includes an introduction to critical thinking, a critical thinking activity, and an explanation of the diversity component.
If directed by your instructor, place the answers to Investigation 1A and Current Weather Studies 1A on the A Answer Form linked from the AMS Weather Studies website.
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