Title: EAS 106 LAB WINTER STORMS: CYCLONES, ANTICYCLONES, FRONTS
1 EAS 106 LAB WINTER STORMS CYCLONES ANTICYCLONES FRONTS Outside the tropics the winds are organized into large systems called low and high pressure areas that produce much of our weather. Highs and lows are typically about 1000 miles in diameter and travel from west to east at about 25 miles per hour. Earths rotation gives them the form of giant wind spirals. Air spirals counterclockwise in toward lows (cyclones) and then is forced to rise. Therefore lows bring mostly cloudy wet weather. Highs (anticyclones) have the opposite circulation. Air spirals clockwise and outward from the center. Then air from above sinks to fill the void. Highs bring mostly clear weather but if sunshine heats the ground enough thunderstorms are possible. As winds spiral into low pressure areas large regions of polar and of tropical air called air masses are brought close together. Temperature contrasts become concentrated in long narrow zones or fronts which are basically boundaries that separate air masses. It is important to identify the fronts and predict their motion because much of the major weather changes and stormy weather outside the tropics forms along fronts. The nextcontains a schematic 3-D illustration of a low pressure area with winds air masses (cold or warm) fronts and clouds. Theafter that shows how weather data is plotted at each city weather station. Then guides for drawing fronts and illustrative examples are shown. Finally come the exercises. WEB Sources NOAA Summaries of Major Winter Storms http//www.hpc.ncep.noaa.gov/winter_ storm_summaries/winter_storm_summaries.shtml Weath er Archive You make the maps http//vortex.plymo uth.edu/u-make.html 2 Cold Front Cold Air Advances Warm Front Warm Air Advances Model Extratropical Cyclone (Low) with Cold and Warm Fronts In the drawing of the low to the left the clouds NE of the warm front should be much wider and continuous as in the warm front drawing above. http//rst.gsfc.nasa.gov/Sect14/Sect14_1c.html 3 The Weather Station Model Each weather map contains weather information from a large number of weather stations across the country. In order to read a weather map we must first know how to read the weather information at each station which is presented in a standard coded form called the weather station model. The station model on thisis highly simplified. The station model on the nextis more complete. T (F) Upper left number. Td (F) Lower left number. Weather symbols (to left). P (0.1hPa) Upper right number Wind direction is parallel to the long shaft. It points from the feathers to the small circle and is named for the direction it comes from. Wind Speed (kt) given by feathers on shaft. Full feather 10 kt. Double circle calm Since sea level pressure is always near 1000 hPa even though it appears as 95.6 hPa (to save space) it is really 995.6 hPa. 4 More Complete Weather Station Model 5 Fronts are designated by thick lines studded with triangles or semicircles that protrude in the direction that the front moves. For a stationary front the triangles and semicircles extend in opposite directions. For an occluded front alternating triangles and semicircles protrude in the direction of motion. When a cold front passes by T can drop more than 10 F in an hour. In the typical cold front (below left) at two times 12 hours apart the cold air (shaded) blows from the ___ and the warm air blows from the __. Temperature changes tend to be more gradual at warm fronts. In the typical warm front (below right) the cold air is on the ___ side and blows from the ___ while the warm air is on the ____ side and blows from the ___. 6 Simple Model of Surface Low Pressure Area 7 Indicators for Finding Fronts 8 Indicators for Finding Fronts 9
The next 3s contain surface weather maps for the storm of 05-06 JAN 2005.
1200 UTC 05 JAN. On this chart isotherms and fronts are analyzed.
0000 UTC 06 JAN. Two charts are overlain. The first chart includes fronts and isobars but no weather stations. The second chart includes the weather station information and retains the fronts.
1200 UTC 06 JAN. Two charts are overlain. The top (or first) chart includes isobars but no weather stations. To see the map with weather stations right click on the chart with isobars click on Order and then click on send to back. Then draw the fronts.
10 Sample Weather Map with Isotherms (10C intervals) and Fronts 11 (No Transcript) 12 To see weather station data right click then click on Order - Send to Back 13
The storm of 30 November to 02 December 2008 produced rain snow and ice across a wide swath in the middle of the USA. The satellite image on the next(taken after the storm had passed and the weather had cleared) shows the ice and snow put down by the storm.
The fours after the satellite image contain surface weather charts for 12 UTC 30 NOV 2006 and 00 UTC 01 DEC 2006. The first chart at each time contains the pressure analysis with isobars at pressure intervals of 4 hPa and the second chart includes weather information at a large range of weather stations. The fifth chart gives conditions at 850 hPa (about 1500 m above sea level). The key to the station model for the 850 hPa chart is given on twos after the surface charts.
Draw Isotherms (5C intervals) and Fronts for the surface charts of 12 UTC 30 NOV 2006 and 00 UTC 01 DEC 2006.
Draw Isotherms (5C intervals) for the 850 hPa chart of 00 UTC. Find a station (if there is one) where air with T 0C on the 850 hPa chart is situated directly over air with T surface chart at the same time (0000 UTC). Briefly explain what type of precipitation you would expect at this station.
Find a station at which you expect temperature to A rise and B fall by 12 UTC on 01 DEC and give your reasons in terms of the fronts and how they might move based on their movement in the 12 hours from 12 UTC on 30 NOV to 00 UTC on 01 DEC.
14 Snow and Ice Cover 03 Dec 2006 MODIS Cumulus Cloud Streets Cumulus Clouds Jet Stream Cirrus Clouds 15 (No Transcript) 16 (No Transcript) 17 (No Transcript) 18 (No Transcript) 19 (No Transcript) 20 Decoded Values for Weather Variables on the 850 hPa Chart 21 (No Transcript)
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