Homework 4: Finding Synpotic Scale Fronts--Inclass Exercise

  1. Analyze the NAM initialized surface isobar and 1000-500 mb thickness field for temperature advection in and around the surface cyclone in the Great Plains.



  2. Analyze fronts (and dry line) for this cyclone on the basis of your analysis in (1) above.



  3. Analyze the same portion of the surface weather map for 15 UTC for fronts and dry line.



    1. Examine the surface weather map and the companion 700 mb chart. Explain how the chart showing 0-1 km helicity is consistent with the flow depicted on the two charts.

      The surface chart shows air emanating from the Gulf of Mexico from southeast to northwest into Oklahoma. These streams of air will be running under strong 700 mb southwesterly flow, with the peak 700 mb winds over Oklahoma. Thus, rotation will be imparted by the vertical wind shear, which is maximum over Oklahoma. When this rotating stream of air is tilted into the vertical, there should be a maximum in helicity where the vertical wind shear is the greatest. This would be over Oklahoma.

    2. Examine the map showing surface based CAPE and CIN and compare to the 0-1 km helicty chart. Discuss the validity of the following statement:

      "... THE MOST FAVORABLE PHASING OF THE UNSTABLE WARM SECTOR AND STRONG VERTICAL SHEAR ENVIRONMENT IS OCCURING ACROSS CENTRAL/N CENTRAL/NE OK..."

      The surface chart shows air emanating from the Gulf of Mexico from southeast to northwest into Oklahoma. These streams of air are carrying high dew point temperatures (and high mixing ratios) northward towards Oklahoma. These streams are also coincident with the tongue of high CAPE values seen on the CAPE/CIN chart. These streams are also entering the area on the 700 mb chart that has the greatest inferred vertical wind shear. Thus, in Oklahoma, once the CIN disappears (and if), there is a phasing of the tongue of greatest instability (CAPE) with greatest vertical wind shear. The statement is valid.