Department of Earth & Climate Sciences Spring 2016 Meteorology 260

Transcription

1 Department of Earth & Climate Sciences Spring 2016 Meteorology 260 Name Laboratory #9 Key: Joplin Tornado Day Subsynoptic, Thermodynamic, and Wind Shear Setting Part A: 1600 UTC Surface Chart Subsynoptic Analyses (100 pts) Part B: 1200 UTC Sounding Analyses (100 pts) Part C: 1200 UTC CAPE Analyses (100 pts) Part D: 1200 UTC Hodograph Analyses (100 pts) Last day to work on in class will be Wednesday April 27, 2016; Lab #10 turn in date is beginning of class 29 April Purpose of this Assignment: Operational and Practical Purposes: o To study the subsynoptic, thermodynamic, and wind shear environments in which the Joplin tornadic thunderstorm developed; Skills and Techniques Learned or Applied o To have the students apply the techniques they have learned in the Skew-T/log P Sounding and hodograph analyses part of the class; o To give students an opportunity to visualize how instability manifests itself in the morning environment in severe weather settings; o To show students how severe weather meteorologists estimate afternoon instability by transforming the morning sounding; o o To show students how to evaluate the instability graphically, and computationally; To introduce students to the finite difference approximation of summation;(integration) graphically and computationally;

2 Part A: 1600 UTC Surface Chart Subsynoptic Analyses Fig. 1: Surface plot with isobars, 1600 UTC 22 May 2011 Figure 1 is the 1600 UTC surface chart on 22 May Isobars are drawn at two millibar intervals, with two labeled. You are also provided a separate clean copy of this chart for your final analyses. (100 pts) 1. On the copy above, draw blue, brown, and red streamlines, as we have have done in class many times to help find important boundaries (10 pts); 2. On the copy above, label all the isobars NEATLY (10 pts); 3. On the copy ablove, label lows and highs (if present) using the correct color convention (10 pts); 4. On the copy above, note that the isobars are strongly kinked away from low pressure in certain locations. It turns out that isobars are strongly kinked usually in areas in which they 2

3 cross boundaries. Using this knowledge, and your results in (1) above, now draw in all the boundaries, using correct symbols and color conventions. (40 pts) 5. Transfer all that you ve done above to the final clean copy. This is what you will turn in and what will be graded. Neatness counts here. (10 pts for Neat Analysis) 6. How does your analysis show that the pre-thunderstorm environment generally matched the prototype associated with severe weather in the Great Plains (20 pts) The prototype surface severe weather pattern in the Great Plains consists of a wave cyclone located over the western Great Plains, with a dry line extending southward. Moist air moves northward ahead of the dry line and is ofen the locus for severe thunderstorm development. The subsynoptic analysis aboves shows such a pattern, with the dry line extending southwestward from the surface wave cyclone over western Oklahoma and into the Texas Panhandle. High dew point air ws moving northward ahead of the dry line over eastern Oklahoma and western Missouri. Part B: 1200 UTC Sounding Analyses (100 pts) You are provided with two color copies of Fig. 1 below, the Springfield MO sounding and hodograph for 12 UTC 22 May

4 Fig. 1: KSGF Sounding and Hodograph, 12 UTC 5/22/11 1. Determine the morning stability at KSGF (Springfield, MO) by analysis of one of the copies of the morning sounding for 1200 UTC 22 May 2011 by completing the following tasks: a. Estimate the height (in millibars) of the Lifting Condensation Level, Level of Free Convection, 500 mb Lifted Index, Equilibrium Level. Be sure to indicate the parcel ascent curve, LCL, LFC and EL right on the diagram. And shade in the areas of CAPE and CIN with proper colors; (30 pts) b. Is the sounding absolutely unstable, absolutely stable or conditionally unstable for a surface lifted parcel. Explain your answer in several sentences. (20 pts) This is a conditionally unstable sounding. The LCL is at about 950 mb (129 m AGL), the LFC is at about 700 mb (~2702 m AGL), and the EL is at about 230 mb (~11,018 m AGL). The Lifted Index is On the second copy of the sounding for for 1200 UTC 22 May 2011 (second copy), estimate the afternoon stability at KSGF (Springfield, MO by completing the following tasks: a. Estimate the Convective Temperature, Convective Condensation Level and determine if the sounding is potentially unstable. Indicate the Convective Temperature (CT), Convective Condensation Level (CCL), and afternoon parcel ascent curve, positive area on sounding (CAPE) (shaded red), and negative area on sounding (CIN) (shaded blue); (30 pts) b. Is the sounding you modified for afternoon surface heating potentially stable or unstable for a surface lifted parcel. Explain your answer in several sentences. (20 pts) This is an potentially and absolutely unstable sounding because the CAPE area greatly exceeds the area of CIN (below the CCL). The CCL is at about 775 mb (1787 m AGL), the CT is at about 34C (93F), and the EL is at about180 mb (~12,151 m AGL). The Lifted Index is -12. The CAPE value is 4405 J/kg.. 4

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6 Part C: Calculation of CAPE 1. Calculate the CAPE from the morning sounding using the method discussed in class. You'll be approximating the CAPE crudely (explained in class) by summing up the indidividual contributions of layers approximately 1500 m thick. The table below should get you started. (95 points) The CAPE I calculated was 1065 m 2 /s 2 2. Using the results from (1) above, calculate the maximum vertical velocity at the EL in the morning. (Started in class) (5 points) (Bottom of Table below) The convective vertical velocity I calculated was 46 m/s. Table 1: Temperature Information Obtained from Sounding Analyses (completed in Part B) for KSGF 12 UTC 5/22/11 6

7 Part D: 1200 UTC Hodograph Analyses (100 pts) Table 1 shows the wind directions and speeds observed in the Springfield sounding 12 UTC 22 May Figure 2 is a blank diagram called a hodograph. It allows us to visualize the way wind directions and speeds vary with height. Table 1: Winds and pressures observed in KSGL radiosonde launch, 12 UTC 22 May

8 Figure 2: Blank hodograph paper. Pressure (mb) Height (m) AGL Direction (deg) Speed (kts)

9 Table 2: Wind Directions (deg) and speeds (kts) at selected pressure levels Storm-Relative Helicity (m 2 /s 2 ) Midlevel Mesocyclone Strength 100 Weak No 150 Moderate Yes 250 Strong Yes >350 Violent Yes Meets Strength Threshold for Categorization as Supercell Table 3: Storm Relative Helicity and Mesocyclone Strength 1. Fill in Table 2 with the wind directions and speeds extracted from the radiosonde information in Table 1; (2 pts each for 24 points) 2. Plot an arrow (vector) for each level given in Table 2, as shown in class. Label each arrow near its end with the appropriate level (for example, Sfc). (2 pts each for a total of 10 pts) 3. Put a black dot at the tip of each arrow; (2 pts each for a total of 10 pts) 4. Draw (neatly) straight line segments connecting each dot. (2 pts each for a total of 10 pts) In plain english describe how the the wind in the lowest 6 km, as visualized by the hodograph you just constructed, varied with height. (16 pts) The winds change in a clockwise sense from the surface to around the 700 mb level, and then a slight counterclockwise change and then straight. The winds also generally increasd with height except between 850 mb and 700 mb. Also, noteworthy, is that the surface wind is nearly right angles to the wind in the middle troposphere. 5. The 0-3 km storm relative helicity calculated for this hodograph can be found in the box on the upper right of the sounding. Positive values of this parameter indicate that inflow air entering the updraft of any developing thunderstorm would be rotating. Answer in complete sentences. a. Using the information given in Table 3, categorize the potential strength of the midlevel mesocyclone of any developing thunderstorm; (20 pts) The 0-3 km storm-relative helicity for this case is 445 m 2 /s 2. According to the values given in Table 3, any thunderstorm devleoping in this environment would develop a rotating updraft characterized as a violent mesocyclone. b. How do your values in Table 2 and the plotted hodograph conceptually indicate that the updraft of any developing thunderstorm on this day would be helical (rotating)? (20 pts) 9

10 Both the values in Table 2 and the wind plots on the hodograph indicate that the surface wind field is nearly at right angles to the winds at 500 mb. This suggests that the surface wind flow would develop great rotation that, when tilted into the vertical by the updraft of the thunderstorm, would be associated with a significant counterclockwise rotating updraft, a mesocyclone. 10