In this exercise, you will examine surface, satellite, SST, and model data from 11-13 March 1993 via the Integrated Data Viewer for the Superstorm of 1993 that affected the eastern half of the United States.

The data for this exercise is housed on a server at Central Michigan University. The exercise contains links to IDV Bundle files that will automatically access and display the data needed to answer the questions in the exercise. To do the exercise, download the bundle below and open it within the IDV. This bundle will load a webpage within IDV that will allow you to load each bundle simply by clicking on it. If you are already viewing this webpage from within the IDV's HTML Browser, you do not need to download this bundle.

http://dendrite.cst.cmich.edu/SOC_IDV/SOC_idv_page.xidv

If you prefer, the bundles can also be downloaded to your system by opening the link below in a web browser.

http://dendrite.cst.cmich.edu/SOC_IDV/SOC_idv_bundles.tar.gz

The data for this case can also be accessed directly via THREDDS and ADDE servers:

THREDDS: http://waterspout.cst.cmich.edu:8080/thredds/catalog.xml

- In the tree, expand "Other Data", then "Case Studies", then "Storm of the Century"

ADDE: waterspout.cst.cmich.edu

• Select the "SOC" dataset

Let's begin the exercise.

11 March 1993

1. Load the 11March_pt1.xidv bundle.

   1. First expand the "Surface and Thickness" tree in the legend. Values for 12 Z are plotted. You may need to zoom in slightly to make the surface observations visible. Notice the large contrast in temperature between northwest Arkansas and southeast Texas!

      1. Where is the newly developing cyclone at this time?

      2. Using the 1000-700 mb thickness, approximately where is the baroclinic zone located?

   2. Now expand the "500 mb" tree. Values for 12 Z are plotted.

      1. Examine the geopotential height field. Does the trough over the southwest US appear very deep at this time?

      2. Overlay the absolute vorticity and wind barbs. Can you identify any shortwaves that may influence future cyclogenesis?

      3. Where is the PVA/NVA located with respect to any shortwave troughs? Does examining the absolute vorticity advection help you to identify shortwave troughs?

   3. Next expand the "300 mb" tree. Values for 12 Z are plotted.

      1. Is there a jet streak upstream from the developing surface low? If so, where is it located in relation to the trough at 300 mb?

      2. What does this juxtaposition suggest regarding further development of the trough? Examine the temperature advection pattern to assist your answer.

2. Load the 11March_pt2.xidv bundle.

   1. Examine the water vapor imagery.

      1. Is there moisture available for this "young" system in the southwest? How do you know this? At what levels does water vapor imagery depict moisture?

   2. Examine both visible and infrared imagery.

      1. Does any convection develop over the western Gulf of Mexico and eastern Texas?

      2. When does it form? How can you infer that convection is taking place?

      3. What can you infer about the stability in this area?

3. Load the 11March_pt3.xidv bundle.

   1. Examine the ETA model solution at the surface for the next 48 hours.

      1. What happens to the low-pressure center? Where is it located at 48 hours according to the model?

      2. During which time period are the pressure falls the greatest? How much does MSLP decrease during this period?

12 March 1993

1. Load the 12March_pt1.xidv bundle

   1. Examine the Infrared Imagery - zoom in to the Gulf of Mexico

      1. What evidence of cyclogenesis do you see as the associated clouds move through the northern Gulf of Mexico?

      2. Does there appear to be any significant convection present? Are the cold cloud tops becoming more organized? How so?

      3. Examine the sea surface temperatures. Where does the cyclone track with respect to the SST field? Is this particular track beneficial for cyclogenesis?

      4. Considering the latent heat release associated with convection and the strong gradient of SSTs; how do these factors contribute to surface pressure falls?

   2. Examine the Water Vapor Imagery - zooming back out for a wider view

      1. See the text note in the "Displays" tab in the Dashboard for a description of the four types of darkening identified by Weldon*. Which (if any) of the four types of darkening as identified by Weldon can be observed during this time period?

      2. Describe the type, time period, and location.

2. Load the 12March_pt2.xidv bundle

   1. First expand the "500 mb" tree, containing a 48 hour ETA forecast from 12 Z.

      1. How has the 500 mb pattern evolved since we examined it on 12Z 11 March?

      2. During the forecast period, do you see evidence of waves phasing (northern and southern wave trains)? Examining the absolute vorticity may help visualize this.

   2. Expand the "300 mb" tree, containing a 48 hour ETA forecast from 12Z.

      1. Identify any jet streaks present at the initial time, with respect to the surface low.

      2. Describe the evolution of the cyclone in relation to the jet streaks, in terms of the four quadrant model for straight line jet streaks.

      3. Overlay the divergence. How far from the jet streak cores is divergence maximized? Is the divergence correlated more with the jet max itself or the isotach gradient?

   3. Next, expand the "850 mb" tree, containing a 48 hour ETA forecast from 12Z.

      1. Where do any low level jets develop? Describe their evolution through time.

      2. What role can low level jets play in the development of significant precipitation?

   4. Lastly, expand the "200 mb and MSLP" tree containing a 48 hour ETA forecast from 12Z.

      1. Can you identify and track a tropopause undulation? Where is it? How can you identify it? [Hint: think what happens when stratospheric air sinks]

      2. Overlay the MSLP. Where is the undulation in relation to the surface cyclone? Does this fit the conceptual model?

13 March 1993

1. Load the 13March_pt1.xidv bundle

   1. Examine the Infrared Imagery.

      1. Can you identify the warm conveyor belt, the cold conveyor belt, and the dry conveyor belt? What satellite features help indicate their presence? Referring to the following resource may help:

         "Cyclogenesis: Analysis utilizing Geostationary Satellite Imagery" by Dan Bikos, et. al.

         http://rammb.cira.colostate.edu/visit/cyclo/title.asp(Must be opened within a web browser)

      2. Examine the total snowfall from 12-14 March via the image in the Omni display window**. Was the heaviest snow associated with the coldest cloud tops? Why or why not?

   2. Examine the Water Vapor Imagery.

      1. See the text note in the "Displays" tab in the Dashboard for a description of the four types of darkening identified by Weldon*. Which (if any) of the four types of darkening as identified by Weldon can be observed during this time period?*. Describe the type, time period, and location

      2. Utilizing only the satellite imagery, approximately when did the storm reach its maximum intensity? What satellite feature tells you this?

2. Load the 13March_pt2.xidv bundle

   1. First expand the "300 mb and MSLP" tree, containing a 48 hour ETA forecast from 00 Z.

      1. When do MSLP falls decrease?

      2. As MSLP falls diminish, how does the cyclone become oriented with respect to the 300 mb jet streak?

   2. Next expand the "850 mb" tree

      1. How strong does the low-level jet become during the forecast period?

         1. Is this value impressive?

      2. How is the low-level jet positioned in relation to the upper-level jet-streaks noted in the previous question?

      3. Overlay temperature advection. How does the thermal advection pattern match up to the location of the low-level jet?

      4. Overlay theta-e advection. Over what area of the US does this parameter maximize? What does this parameter tell you physically about what is happening?

   3. Finally, expand the "Snowfall in cm 12^th to 14^th" tree.

      1. Compare the model forecast precipitation with what actually occurred (via the image in the omni display). If a generic 10:1 snow to liquid ratio is applied, the precipitation displayed by the model is equivalent to snowfall in cm. Are the amounts reasonable? Did the model place the precipitation correctly?

* = Weldon, R. B., Holmes, S. J., 1991, Water Vapor Imagery, Interpretation and Applications to Weather Analysis and Forecasting; NOAA Tech. Rpt. NESDIS 57, 213 pp.

** = Kocin, P.J., et. al., 1995: Overview of the 12-14 March 1993 Superstorm. Bull. Amer. Meteor. Soc., 76, 165-182.