Department of Geosciences Name San Francisco State University Spring 2012 Metr 201 Monteverdi Quiz #5 Key (100 points) 1. Fill in the Blank or short definition. (3 points each for a total of 15 points) (a) (b) (c) (d) (e) Outflow boundary -- the leading edge of the cold outflow whose source is the downdraft in a thunderstorm. Loaded Gun Sounding -- a sounding in which warm moist air at the surface is surmounted by potentially warmer air above an elevated inversion. As diurnal warming at the surface modifies the base of the sounding, the potential CAPE value continues to increase with no perceptible weather until and if the convective temperature is achieved, at which time explosive convection occurs with much greater CAPE than in the initial sounding. Cyclone -- an area of low pressure completely encircled by at least one isobar or height contour. hook echo a hook-like appendage on radar reflectivity products that occurs because a mesocyclone circulates precipitation from the forward flank of a thunderstorm counterclockwise around the updraft area. The development of cold air downdrafts, precipitation at ground level, the anvil and lightning appear roughly simultaneously when a cumulus congestus cloud becomes cumulonimbus. This is apparently related to the formation of hail at the portion of the cloud at or near the freezing level. 2. Symbols. Provide the correct symbol (2 pts each for a total of 8 pts) Example: acceleration of gravity g vertical wind component w potential temperature horizontal wind component along x-axis horizontal wind component along y-axis θ u v
3. 500 mb chart (21 pts). Examine the 500 mb chart given below. a. The contours on this chart are HEIGHT contours of the 500 mb surface. Explain what that means in this case. (10 points) The height contours indicate the height above sealevel at which the radiosonde detected a pressure of 500 mb. b. With a long arrow drawn tangent to the flow, indicate the POLAR JET STREAM. (5 points) c. Locate one trough axis and one ridge axis and one cyclone, by placing the correct COLORED symbols on the chart. (6 points) 2
4. Use and Interpretation of Weather Maps and Charts (Multiple Choice (circle best answer) and Short Answer) (56 points in this section) (a) Figure 2 is the surface chart for 1700 UTC 11 May 2011. The location of Pressure System A and the boundaries Lines A, B, D and D are indicated. (20 pts) 1. Place (draw) the correct COLORED symbols or Pressure System A and the boundaries noted as Lines A, B and C. (9 pts) 2. The boundary labeled Line D is an outflow boundary. (3 pts) 3. The boundary labeled Line C represents the leading edge of what? (several sentences here, please). (8 pts) Line C is a warm front. It represents the leading edge of advancing warm air, in this case, streaming northward from the Gulf of Mexico. As the warm front passes northward, temperatures should locallly increase sharply for stations currently north of the front 3
(b) Figure 3 is a chart of CAPE and CIN for 1600 UTC 11 May 2011 Notice the locations A and B, where the CAPE values are 2100 and 4000 J/kg, respectively. Location A is Oklahoma City. The blue areas represent areas of CIN. (16 points) 1. Assume thunderstorms develop at both locations. At which location will the thunderstorm's updrafts be stronger and why? (8 pts) (Two or three sentences) Since the vertical velocity associated with buoyancy is directly proportional to the CAPE, the thunderstorm updrafts would be stronger at location B, where the CAPE values are nearly twice that as those at A. 2. At which of the two locations might you expect thunderstorms would be forming at the time of the chart and why? (8 points) (Two or three sentences) One would expect thunderstorms to be in the process of formation at location B. This is because there is no CIN shown at location B. Thus, the atmosphere is absolutely unstable at location B and the LFC is at the ground. At location A, Oklahoma City, there is still considerable CIN, which means that the LFC is not at the ground. Although thunderstorms may shortly begin to form at Oklahoma City, they are not likely to be occurring until the CIN value is reduced somehow. 4
(c) Figure 4 is the 12 UTC 11 May 2011 sounding for Oklahoma City. It corresponds to the location A shown in Figure 3. (14 pts) 1. Determine the CCL, CT and EL for afternoon heating by drawing on the chart. Also indicate the area of afternoon sbcape (in red). EL = 180 mb; CT = 33 C (92F); CCL = 760 mb. (9 pts) 5
2. Figure 5 is a chart that shows maximum temperatures anticipated for this afternoon (in F). Using your results in the previous question, comment on how likely it is that thunderstorms will form in the Oklahoma City area during the afternoon. Use the web conversion table on our website to convert from Centigrade/Fahrenheit (5 pts) The convective temperature for this sounding is approximately 92F. The maximum temperature is expected to be slightly greater than 80F. Thus, it is unlikely that thunderstorms will form due to diurnal heating alone, unless other aspects of the sounding are transformed. 6
(d) Figures 6 and 7 are the Categorical Convective Outlook and the Probabilistic Tornado Outlook for 11 May 2011. (6 pts) Figure 6: Categorical Convective Outlook for 11 May 2011 Figure 7: Probabilistic Tornado Outlook for 11 May 2011 7
1. On the Convective Outlook for May 11 (Fig. 6). The green (outermost) shaded area encompasses (2 pts) a. the region that has a 10% probability that strong and violent tornadoes will be observed within 25 miles of a given location. b. the portion of the United States expected to experience general thunderstorms. c. the portion of the United States expected to experience tornadoes. d. the region in which severe downbursts are sure to occur. e. the portion of the United States expected to have a high risk for severe thunderstorms. 2. The Tornado Outlook (Fig. 7) outlook basically shows (2 pts) a. the chances that rain will also have hail mixed with it. b. the probabilities that severe storms will occur. c. the probabilities that tornadoes will be observed within 25 miles of a given point. d. the probabilities that hail will occur at a given location. e. None of the above. 3. The hatched area on the Tornado Outlook (Fig. 7) encompasses (2 pts) a. the region that has a 10% probability that strong and violent tornadoes will be observed within 25 miles of a given location. b. the portion of the United States expected to experience general thunderstorms. c. the portion of the United States expected to experience tornadoes. d. the region in which severe downbursts are sure to occur. e. the portion of the United States expected to have a moderate risk for severe thunderstorms. 8