Prerequisite Skills Test

Instructions:

Please answer following questions below. We ask that you submit your answers in either a MSWord formatted document or in a plain-text file. Email your document to dbabb@ems.psu.edu. We will evaluate your responses and notify you via return email of our assessment.

Note: We suggest that you print off this page (you may want to print/save some of the maps and images as well). You can save an image to your local hard drive by bringing up the image in the browser window and then clicking "File->Save As..."

1. Consider a loop of IR images that spans from 1215Z to 1745Z on February 15, 2011.  Examining that image loop, you notice a strange shading reversal that takes place over Texas (One half the state seemingly goes from light to dark while the other half goes from dark to light).  This question will explore this oddity.
   1. Start by briefly describinng how IR imagery is obtained.  Discuss what is being measured versus what is being displayed in this image.  What fundamental assumption do meteorolgists make when determining cloud top heights from IR imagery?
   2. Now, in a brief paragraph or two, describe what is transpiring meteorologically in this loop of IR images. To assist in your explanation, I have provided the beginning and ending frames from this loop (1215Z and 1745Z) as still images (and reference points "A" and "B").  Please tailor your explanation for someone who is unfamiliar with basic meteorological conepts.
2. You are given station-model maps of Pennsylvania at 12Z and 13Z on December 11, 2002. Note that "UNV", the three-letter station identifier for the University Park Airport in State College, Pennsylvania, marks the corresponding station model on both maps.

   You are also given an observed skew-T (at 12Z) and three forecast skew-T's (see table below). The three forecast skew-T's were valid at 13Z, 14Z and 17Z. They were based on a computer's prediction made at 12Z on December 11, 2002.

   Observed	Forecast skew-T
   12Z	13Z	14Z	17Z

   1. You are given a national radar image at 12Z on December 11, 2002. The large shield of precipitation in the East was advancing steadily to the northeast. The white dot marks the location of the University Park Airport. Given the intensity of the radar echo over University Park Airport, explain why the 12Z map of station models indicates that no precipitation was reported at 12Z at UNV (precipitation was not reaching the ground). In your discussion, include reason(s) why precipitation was not reported at the surface. As before, your answer should efficiently and effectively explain relevant concepts leading to this occurrence.
   2. Now compare the 12Z skew-T to the forecast skew-T's at 13Z and 14Z. There is obviously a difference in appearance between the 12Z skew-T and the 13Z skew-T, as well as the 13Z skew-T compared to the 14Z skew-T. The differences are most notable in the lower troposphere. How and why did the lowest layers evolve from the 12Z skew-T into the 13Z and 14Z skew-T's? Please reference specific times and temperatures in your explanation and focus on relevant meteorological concepts which led to the changes in both the temperature and dew point soundings between 12Z and 14Z.
   3. Precipitation was first reported at UNV at 15Z. Was precipitation falling at 17Z? Briefly but cogently explain. Use the 17Z forecast skew-T to support your answer.  If your answer was "yes" please include a descussion of what form the precipitation took.
3. The great snowstorm on the weekend before Presidents' Day 2003 had a very humble beginning. To see the humility of the storm's beginning, you are given the surface and 500-mb analyses at 00Z on February 16, 2003.  On the surface map, note the early stages of the cyclone as the embryonic low starts to take shape over Louisiana at an unimpressive 1007 mb.  This question will explore the early intensification of this storm.
   1. You are given the 500-mb analysis of absolute vorticity at 00Z on February 16, 2003. What is the most likely position of the "vort max" in the southern branch of strong 500-mb winds that's directly associated with the early stages of the surface low over Louisiana? To answer this question, you must address each of the following issues:
      • Give a specific geographical location of the vort max. You must pinpoint the location of the vort max with a specific reference to the region of a state (for example, "northwest Oregon").
      • What's the full name of the "feature" on the 500-mb analysis that's directly linked to the "vort max" (this name describes what the feature is and how big it is)?
   2. Imagine a parcel of air at the center of the 500-mb "vort max". Now imagine riding along with the parcel in time. Discuss the two physical changes that the parcel undergoes as it approaches the surface low in Louisiana. You must be very specific here.
   3. In light of these physical changes, what process does the parcel undergo to the east of 500-mb vort max?
   4. What impact does this process have on surface pressures over eastern Louisiana? Explain, bringing a representative air column into your discussion. Limit your explanation to a single paragraph.
   5. Look at the 12Z surface analysis on February 16, 2003. Identify a region of strong cold air advection located near the developing low pressure and describe how you arrived at this answer. 
   6. Finally, describe in no more than two paragraphs how cold advection in this region acts as a positve feedback mechanism helping to intensify the low pressure system.
4. You are given the 24-hour prog from a computer model.
   1. What is the prog's initialization time? What is its valid time?
   2. Describe what data fields appear on each panel of the 4-panel prog?  State why are each of these variables are important to the forecaster.
   3. A television weathercaster in Wilkes-Barre/Scranton, Pennsylvania is using this prog in order to make a local forecast its valid time, and asks you for help. Incorporating the information from this prog, help the weathercaster to formulate a precipitation forecast (onset, amount, and type) for Wilkes-Barre/Scranton for the prog's valid time. Please be advised that your answer cannot exceed the precision of the forecast prog you are given.
   4. Later that evening around 10 P.M., the weathercaster looked at the 12-hour and 18-hour progs from the latest model run.
      • On the 11 P.M. news, should the weathercaster adjust his/your forecast cited in part iii? If so, why? You must cite specific evidence to support your claim.
      • If no adjustments to timing are necessary, explain your reasoning in one or two cogent sentences.
      • If an adjustment is necessary, how should the weathercaster adjust his timing? What should he say on-air about the starting time of precipitation at Scranton? Again, to support your answer, you must cite specific evidence from the prog's forecast for precipitation. Please be advised that your answer cannot exceed the precision of the forecast prog you are given.