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 Practice Problems: Skew-T Plotting

METEOROLOGIST JEFF HABY

Practice Problems: Skew-T Plotting

Get out your laminated Skew-T, erasable markers, and learn these plotting problems. Anwers are provided after each question set. Let me know if any problem or solution is unclear and I will help.

First question set:

1. The surface pressure in Denver, Colorado is given as 850 mb. The temperature is 5 C with a dewpoint of -5 C. What is the surface Relative Humidity in Denver using the information provided? Circle best answer below.
a. 68%
b. 58%
c. 48%
d. 38%

2. The surface pressure in Columbus, MS is 1020 mb. The Relative Humidity is 60% and the Temperature is 10 C. What is the surface dewpoint in Columbus, MS using the information provided? Circle best answer below. Hint: Find saturation mixing ratio through the temperature and multiply by 0.6 to get actual mixing ratio. With the actual mixing ratio the dewpoint can be found.
a. 6 C
b. 3 C
c. 0 C
d. -3 C

3. The surface pressure is 1000 mb. The temperature is 35 C with a dewpoint of 22 C. What is the LCL? Circle best answer below.
a. 680 mb
b. 730 mb
c. 780 mb
d. 830 mb

4. The LCL is located at 850 mb and the surface temperature is 27 C at the 1000 mb surface. What is the surface dewpoint? Hint: from surface draw a line parallel to DALR through temperature to the LCL pressure surface; from LCL point drop down parallel to mixing ratio to the surface pressure and read off dewpoint. Circle the best answer below.
a. 16 C
b. 18 C
c. 20 C
d. 22 C

5. The surface is located at 950 mb. The temperature is 70 F with a dewpoint of 50 F. What is the surface Wet Bulb Temperature? Circle the best answer below.
a. 64 F
b. 61 F
c. 58 F
d. 55 F

6. The surface pressure is 1000 mb. The temperature is 38 F with a dewpoint of 27 F. Rain falls and gradually saturates the surface air to the Wet Bulb Temperature. Assuming precipitation remains as a liquid form as it falls and no other temperature or moisture processes are present, will the rain change to freezing rain? (Find Wet Bulb using temperature and dewpoint given; rain will change to freezing rain if Wet Bulb is 32 F or lower)

a. YES, the rain will change to freezing rain (Wet Bulb is 31 F)
b. NO, the rain will not change to freezing rain (Wet Bulb is 33 F)

#7 - #10: Air in the foothills of Colorado has a Temperature of 50 F and a dewpoint of 32 F. The pressure surface is 750 mb in the foothills. The air advects toward the east and downslopes adiabatically to the 900 mb pressure surface in Kansas.

7. What is the Relative Humidity of the air when in the foothills of Colorado? Circle best answer.
a. 69%
b. 59%
c. 49%
d. 39%

8. What is the Temperature of the air once it reaches the 900 mb pressure surface in Kansas? Circle best answer.
a. 107 F
b. 97 F
c. 87 F
d. 77 F

9. What is the Dewpoint of the air once it reaches the 900 mb pressure surface in Kansas? Circle best answer.
a. 17 F
b. 27 F
c. 37 F
d. 47 F

10. What is the Relative Humidity of the air once it reaches the 900 mb pressure surface in Kansas? Circle best answer.
a. 13%
b. 23%
c. 33%
d. 43%

1. C
2. B
3. D
4. A
5. C
6. B
7. C
8. D
9. C
10. B

Second question set:

1. The surface pressure is 1000 mb. The surface temperature is 40 F with a dewpoint of 25 F. What is the surface RH?
a. 73%
b. 63%
c. 53%
d. 43%

2. Using same information as in #1, what is the temperature of the surface parcel once it is force lifted adiabatically to the 500 mb level?
a. -40 C
b. -30 C
c. -20 C
d. -10 C

3. Using information in #2, if the 500 environmental temperature is - 20 C, what is the LI?
a. 0
b. 10
c. 20
d. -10
e. -20

4. How would you operationally describe this LI value in #3?
a. Very unstable since the surface is warm with a high dewpoint
b. Very stable since the surface is warm with a high dewpoint
c. Very stable since the surface is cold with a low dewpoint
d. Very unstable since the surface is cold with a low dewpoint

5. The surface pressure is 1000 mb. The surface temperature is 27 C with a dewpoint of 13 C. The 500 mb temperature is -15 C. If the temperature decreases linearly with height, what is the freezing level?
a. 540 mb
b. 640 mb
c. 740 mb
d. 840 mb

6. Using the information in #5, what is the surface dewpoint depression?

Write surface Tdd in the following blank: delta ________ C

7. The surface pressure is 1000 mb. The surface temperature is 83 F with a dewpoint of 63 F. The 500 mb temperature is 0 F. The surface parcel air is force lifted adiabatically to the 500 mb level. The environmental temperature decreases linearly with height from the surface to 500 mb. What is the LI? (LI is always degrees C difference)
a. -3
b. -7
c. -11
d. -15

8. Using the information in #7, what is the freezing level of the environmental temperature?
a. 590 mb
b. 660 mb
c. 730 mb
d. 800 mb

9. Using the information in #7, at the LCL pressure level, is the parcel temperature warmer or colder than the environmental temperature?
a. Parcel warmer
b. Parcel colder

10. Using the information in #7, at the 700 mb level, is the parcel temperature warmer or colder than the environmental temperature?
a. Parcel warmer
b. Parcel colder

1. C
2. A
3. C
4. C
5. B
6. 14
7. C
8. B
9. B
10. A

Third question set:

Plot the temperature and dewpoints for each pressure level below, determine the: SB CAPE classification, LI, SWI, TT index, and K index. Temperature and dewpoint changes with height are linear (connect with straight lines) between pressure levels given.

```Pressure Level		    Temperature    	      Dewpoint

1000 mb (sfc)			18 C			12 C
900 mb				16 C			15 C
850 mb				19 C			16 C
750 mb				10 C			5 C
700 mb				5 C			-5 C
600 mb				-5 C			-10 C
500 mb				-15 C			-28 C
400 mb				-26 C			- - -
300 mb				-38 C			- - -
200 mb				-44 C			- - -
150 mb				-45 C			- - -
100 mb				-48 C			- - -
```

1. What is the SB CAPE?
a. 0
b. Positive
c. Large
d. Extreme

2. What is the LI? (see lecture notes for formula and operational interpretation)
a. 8.5
b. 3.5
c. -3.5
d. -8.5

3. What is the SWI? (see lecture notes for formula and operational interpretation)
a. 11
b. 6
c. -6
d. -11

4. What is the TT index? (see lecture notes for formula and operational interpretation)
a. 65
b. 55
c. 45
d. 35

5. What is the KI? (see lecture notes for formula and operational interpretation)
a. 50
b. 40
c. 30
d. 20

Answer the questions below that relate to the sounding you plotted.

6. Which two indices indicate stable air from the operational interpretation?
a. TT and KI
b. SWI and TT
c. LI and SWI
d. SB CAPE and LI

7. What causes the two indices in #6 to be stable?
a. Low dewpoints at 850 mb
b. Stable temperature profile between the surface and 850 mb (low level inversion)
c. High 700 mb dewpoint depression
d. Very warm and moist PBL

8. Why is the parcel that is raised from 850 mb pressure surface much more unstable than the parcel raised from the 1000 mb pressure surface?
a. Condensational warming is much more significant in the rising parcel originating from 850 mb pressure surface
b. The parcel that originates from the 850 mb pressure surface starts out much warmer in its temperature as compared to the starting temperature of the 1000 mb parcel
c. The dewpoint depression increases from 850 to 700 mb
d. Parcel originating from the 850 mb pressure surface produces significant CAPE while the 1000 mb parcel does not

9. Which of the following would most likely lead to very strong thunderstorms if occurring with this sounding?
a. Low level convergence that forces air to rise from surface
b. Mid-level subsidence caused from ridging
c. Strong shortwave that forces tropospheric air between 900 and 800 mb upwards
d. A warming of the 500 mb environmental temperature

10. What is the surface relative humidity?
a. 83 %
b. 68 %
c. 53 %
d. 38 %

11. (by visual inspection) A parcel lifted from which pressure level will generate the highest CAPE (MU CAPE)?
a. 950 mb
b. 900 mb
c. 850 mb
d. 800 mb
e. 750 mb

12. (by visual inspection) A parcel lifted from which pressure level will generate the least amount of CAPE?
a. 950 mb
b. 900 mb
c. 850 mb
d. 800 mb
e. 750 mb

1. A
2. B
3. D
4. A
5. B
6. D
7. B
8. D
9. C
10. B
11. C
12. A

Fourth question set:

Plot the following data:

```Pressure       Temperature         Dewpoint
1000mb	  22 C		     17 C
800mb		  15 C		      0 C
600mb		   0 C		    -20 C
```
1. What is the mixing ratio and saturation mixing ratio at each pressure level above?

2. What is the RH at each pressure level above?

3. Using 1000 mb as the surface, what is the surface based LCL?

4. What is the 600 mb wet-bulb temperature?

5. If the air at 800 mb downslopes to the 1000 mb pressure surface, what will be the temperature, dewpoint and RH of the air once it reaches 1000 mb?

6. What is the 1000 to 600 mb column RH using the 3 RH values that can be calculated?

7. If the 500 mb temperature is -15 C, what is the LI? Surface pressure is 1000 mb

8. If the 1000 mb temperature is 5 C and the 700 mb temperature is -15 C and the temperature decreases linearly with height what is the freezing level?

9. What is the Tdd at each of the 3 pressure levels using data at top of page?

10. If the 1000 mb temperature is 40 F and the 1000 mb wetbulb temperature is 32 F, what is the 1000 mb dewpoint?

1. 1000 mb: w= 12.3 g/kg; ws= 17 g/kg
800 mb: w= 4.8 g/kg; ws= 13.8 g/kg
600 mb: w= 1.35 g/kg; ws= 6.5 g/kg

2. 1000 mb RH= 72%
800 mb RH= 35%
600 mb RH= 21%

3. LCL= 930 mb

4. 600 mb wet-bulb = -7 C

5. 1000 mb T = 34 C; 1000 mb Td = 3 C; 1000 mb RH = 14%

6. (72 + 35 + 21) / 3 = 43%

7. Te = -15, Tp = -11; LI = -15 - (-11) = -4 (unstable)

8. 915 mb

9. 1000 mb Tdd= delta 5 C
800mb Tdd= delta 15 C
600 mb Tdd= delta 20 C

10. 18 F

Fifth question set:

1. Given the data below, what is the BRN? What is operational interpretation of this value?

0-500m mean wind= 15 m/s; 0-6km mean wind= 30 m/s; SB CAPE= 1,500 J/kg

2. Given the data below, what is the EHI? What is operational interpretation of this value?

SB CAPE= 2,100 J/kg; SR HEL= 350 m^2s^-2

3. What three factors each contribute to increasing HELICITY? Why is knowing the HELICITY value important to an operational meteorologist?

4. Given the data below, what is the 0-3 km speed shear in units of s^-1? What is operational interpretation of this value?

Sfc wind speed = 11 m/s; 3 km above surface wind speed = 26 m/s

5. The surface pressure is 950 mb. What is the LCL when the surface temperature is 105 F and the dewpoint is 58 F? What is the surface RH?

6. Why is it important for an operational meteorologist to know the value of CINH and cap?

7. Plot the data below and determine to LI, SWI, TT, KI, LCL, freezing level, LFC, EL. Give operational significance of LI, SWI, TT and KI.

```Pressure level		   Temperature        Dewpoint
Surface (960 mb)		33 C		20 C
900 mb				26 C		18 C
850 mb				25 C	        15 C
800 mb				22 C		13 C
700 mb				11 C		 9 C
600 mb				 3 C		-5 C
500 mb				-7 C	       -15 C
400 mb			       -18 C	       -30 C
300 mb			       -31 C		------
200 mb			       -50 C
100 mb			       -65 C
```

1. 1,500 / (0.5*15^2) = 13.3, optimum for supercells if CAPE and shear both are not too low (which they are not too low in this case)

2. EHI = (CAPE * SR HEL) / 160,000 = 4.6 (powerful tornadoes possible if storms develop)

3. 0 to 3 km speed shear, 0 to 3 km directional shear, 0 to 3 km high average wind speeds. High HELICITY makes updraft rotation more likely when a storm develops. This can help lead to tornadoes.

4. delta 15 m/s / 3,000 m = 0.005 s^-1 = 5 shear units (moderate speed shear)

5. 655 mb, RH = 20%

6. Surface based convection will not occur until there is either enough lift forcing or the CINH and cap have weakened to zero.

7. LI = -6 (large instability)

SWI = -4.5 (high end of marginal instability)

TT = 54 (widely scattered severe storms possible)

KI = 45 (high convective potential)

LCL = 800 mb

Freezing level = 570 mb

LFC = 725 mb

EL = 195 mb