San Francisco State University Name Department of Earth & Climate Sciences Fall 2017 Part 1: Fronts Final Inclass Exercise (Inclass Exercise 11) Diagnosing Fronts and Upper Tropospheric Divergence Patterns (200 pts; Due Last Day of Class 12 December 2017) You are provided with (a) 0000 UTC 29 Feburary 2012 plot of surface isobars and 1000-500 mb thickness; (b) a plot of surface observations at 1449 UTC 29 February 2012; (c) 0000 UTC 29 Feburary 2012 Skew-T Plot for Davenport IA (KDVN); (d) 1200 UTC 29 Feburary 2012 Skew-T Plot for Oklahoma City (KOUN); (e) Analysis of 850 mb temperature advection (K o s -1 ) Exercises 1. You will obtain from the Plymouth State University Weather Center Archive at http://amser.org/index.php?p=amser--resourceframe&resourceid=278 Meteograms for Oklahoma City (KOKC) and Davenport IA (KDVN); (0000 UTC Start Time 29 February 2012). (12 pts) 1
2
2. Each person will analyze the provided charts (a) (midsection of country only) and (b), using standard techniques (40 pts) 3
4
3. Each person will compare/contrast his/her analysis of (a) with the actual 850 mb 1 temperature advection analysis given in (e) (8 pts) While the geostrophic temperature advection analysis on nam_thick shows strong cold advection in eastern New Mexico and north of the warm front in Iowa, Minnesota, and Wisconsin in the same locations as shown by the 850 mb temperature advection plot, there were some significant differences. The actual temperature advection plot shows very strong cold advection northwest of the surface low in eastern Wyoming and northwestern Nebraska and strong warm advection ahead of the dryline in central Texas that my analysis did NOT show. 1 850 mb is roughly at the surface in this area. 5
4. Each person will examine the provided soundings in (c) and (d) to find evidence that backs the frontal analyses in (a) and (b). (10 pts) The KDVN sounding indicates strong veering of the wind, consistent with strong warm advection on the cold air side of a warm front. The strongest veering is coincident with the inversion that is quite low in the troposphere, at around 850 mb. This indicates that the warm front is quite nearby, and consistent with my positioning of the warm front in southern Iowa/northern Missouri. The KOKC sounding shows strong backing of the wind with height, particularly from around 600 mb up through 300 mb, consistent with the cold advection area on the cold air side of a cold front. The inversion at around 700 mb indicates that the surface cold front passed OKC some hours ago and would be southeast of OKC. And both of these observations are consistent with the projected position of the cold front that would be southeast of OKC. 5. Each person will write one paragraph describing how your findings in (2) and (3) just above are supported by the information in the Meteograms. (20 pts) The meteogram for KDVN indicates a wind shift from southeast to southwest and a temperature rise around 11 UTC, which is in the middle of the night. This is consistent with a warm front passage, which one would expect given the surface analysis showing the warm front moving northward, just on the Iowa-Missouri border. The meteogram for KOKC shows a temperature fall around 02 UTC, an abrupt dew point fall, and a marked wind shift from southerly to westerly at around that time, indicating a cold frontal passage. At 01 UTC, the surface analysis indicates a cold front northwest of OKC, moving southeastward. Hence, this analysis is consistent with the passage of that front over the OKC area in several hours. Presentations (~2 minutes each) (10 pts) 1. (2a) Juliana 2. (2b) Drew 3. (3) Jonathen 4. (4) Tianny 5. (5) Natalie 6
Figure (a): 0000 UTC 29 Feburary 2012 plot of surface isobars and 1000-500 mb thickness; 7
Figure (b) plot of surface observations at 1449 UTC 29 February 2012 8
Figure (c): 0000 UTC 29 Feburary 2012 Skew-T Plot for Davenport IA (KDVN); 9
Figure (d): 1200 UTC 29 Feburary 2012 Skew-T Plot for Oklahoma City (KOUN); 10
Figure (e): 0000 UTC Analysis of 850 mb Temperature Advection (K o s -1 ) 11
Part 2: Divergence Patterns Diagnosed from Vorticity Patterns You are provided with (f) 0000 UTC 29 Feburary 2012 plot of 300 mb heights (m). (g) 0000 UTC 29 Feburary 2012 plot of 300 mb heights (m) and absolute vorticity (X 10-5 s -1 ). (h) 0000 UTC 29 Feburary 2012 plot of 300 mb convergence (X 10-5 s -1 ). Exercises 6. Each person will analyze troughs and ridges on (f) and, using ERTH 260 reasoning, make a first guess on divergence/convergence patterns at 300 mb for the middle third of the country; (20 pts) Divergence should be occurring broadly between the main trough acis over western TX to Wyoming to the ridge axis over the Mississippi River Valley. But there is a second short wave coming into the area over Utah that should have some divergence ahead of it too. 12
7. Each person will shade in the absolute vorticity advection areas you deduce on (g) using the following convention: (i) light green shading for areas of positive (cyclonic) absolute vorticity advection; (ii) light brown shading for areas of negative absolute vorticity advection. Now, deduce where divergence and convergence areas are on this chart. (One paragraph) (40 pts) Divergence areas should be in the areas of cyclonic (positive) vorticity advection and convergence in the area of anticyclonic (negative) vorticity advection. 8. Each person will examine the plot of 300 mb convergence patterns given in (h) and compare and contrast the results you got in (6) with the actual patterns given in (h) (30 pts The major areas of actual divergence over western Oklahoma and the Texas Panhandle and convergence over Colorado and northern New Mexico agree with my estimates. Also, the prong of convergence over west TX between the two divergence areas was captured well. However, there are significant areas of disagreement. The second area 13
of divergence associated with the second shortwave was actually much further north than my estimate from the vorticity advection areas. Presentations (~2 minutes each) (10 pts) 9. (6) Juliana 10. (7) Drew and Tianny 11. (8) Jonathen and Natalie Figure (f): 0000 UTC 29 Feburary 2012 plot of 300 mb heights (m). 14
Figure (g): 0000 UTC 29 Feburary 2012 plot of 300 mb heights (mm) and absolute vorticity (X 10-5 s -1 ). 15
Figure (h): 0000 UTC 29 Feburary 2012 plot of 300 mb convergence (X 10-5 s -1 ). 16