DEPARTMENT OF GEOSCIENCES                                   Name____________________

San Francisco State University                                                Metr. 201 Spring 2011

 

Metr 201 -- Monteverdi
Quizzes #5 and #6 (conjoined) 200 pts.

 

1.     Fill in the Blank or short definition.  (CHOOSE 3:  6 points each for a total of 18 points in this section).


(a)          Outflow boundary --  the leading edge of the cold outflow whose source is the downdraft in a  thunderstorm.

(b)          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.

(c)        Cyclone --  an area of low pressure completely encircled by at least one isobar or height contour.

 

(d)        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.

 

(e)        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. Units.  Provide the metric units used conventionally for the following (6 pts each for a total of 30 pts)

           

Example

            Acceleration                 meters per sec2 or m s-2

 

           

    CAPE                                                          _______J kg-1_________________

 

    Lifted Index                                                ________C or K________________

 

    frictional acceleration                                  _________ m s-2_______________

 

   500 mb height                                             _________m or dm_______________

 

    Coriolis acceleration                                    ________ m s-2________________

 

 

 

 

 

3.  500 mb chart (40 pts).

 

Examine the 500 mb chart given below. (40 points in this section).

 

 

 


a.  The contours on this chart are HEIGHT contours of the 500 mb surface.  Explain what that means in this case. (15 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.  (10 points) (See map)

 

 

c.  Locate one trough axis and one ridge axis and one cyclone, by placing the correct symbols on the chart.  (15 points) (See map)

 

4. Use and Interpretation of Weather Maps  (Multiple Choice (circle best answer) and Short Answer)  (112 points in this section)

 

(a) Figure 2 is the surface chart for 1700 UTC 11 May 2011.  Note the  location of Pressure System A and the boundaries noted as Lines A, B, D and D. (35 pts)

 

1.         Place (draw) the correct symbols  for Pressure System A and the bounadies noted as Lines A, B and C.       (20 pts)      (See map)

 

2.         The boundary labeled Line D is an ___outflow boundary_________ .   (5 pts)

 

3.         The boundary labeled Line C represents the leading edge of what?  (several sentences here, please). (10 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.

 

 

(b).      Figure 3 is a chart of CAPE and CIN  for 1600 UTC 11 May 2011   Note 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.  (40 points)

 

1.        Assume thunderstorms  develop at both locations. At  which location will the thunderstorm's updrafts be      

stronger and why? (20 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? (20 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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 (c)       Figure 4 is the 12 UTC 11 May 2011 sounding for Oklahoma City.  It corresponds to the location A shown in Figure 3.  (31 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.  (21 pts)

 

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. (10 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.

 

 

 

(d)      Figures 6 and 7 are the Categorical Convective Outlook and the  Probabilistic Tornado Outlook for 11 May 2011. (6 pts)

1.         On the Convective Outlook for May 11 (Fig. 6).  The green shading  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 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.

 

 

 

 

 

 

 


 

Figure 1:  500 mb Chart.  12 UTC 11 May 2011

 

 

 

 

Figure 2:  Surface Chart, 1700 UTC 11 May 2011 

 

 

 

 

 

Figure 3: Chart of CAPE/CIN , 1600 UTC 11 May 2011

 

 

 Figure 4:   Sounding for Oklahoma City, 12 UTC 11 May 2011.  (Location A on Fig. 3)

Figure 5.  Forecast afternoon temperatures (from RUC model).  Black square shows approximate location of Oklahoma City.

 

 

 

 

Figure 6. Convective Outlook for 11 May 2011.

 

Figure 7.    Tornado Outlook for 11 May 2011