COMET Modules

Question 1

Why do we use ensemble forecasts?

Choose all that apply.

1) Ensembles allow us to account for uncertain initial conditions
2) Models must estimate dynamical and physical processes
3) Ensembles allow us to forecast probabilities for weather events
4) Ensembles allow us to reduce the uncertainty of NWP forecasts

Answer 1

1, 2, 3

Question 2

Which of the following perturbations can be used to make an EPS?

Choose all that apply.

1) Dynamical formulation
2) Initial conditions
3) Model physics
4) Boundary conditions

Answer 2

1, 2, 3, 4

Question 3

Which of the following statements about perturbations of NWP model initial conditions used in EPSs are correct?

Choose all that apply.

1) They are largest where initial conditions are especially uncertain
2) They are placed randomly in the model domain
3) They are determined based on forecast sensitivity to initial condition differences
4) Their value is generally of similar size to observing instrument errors

Answer 3

1, 3, 4

Question 4

True or False? One of the biggest challenges in using EPS forecasts is interpreting the post-processed EPS output.

Answer 4

True

Question 5

Using the ensemble mean to present the EPS forecast data smooths out _____ features and retains the _____ features. This is the main reason that the ensemble mean forecast generally performs ____ the operational forecast in the medium range.

Answer 5

small-scale
larger-scale
better than

Question 6

Which of the following statements about EPS spaghetti diagrams are true?

Choose all that apply.

1) They allow the forecaster to see all contour value(s) of all ensemble member(s)
2) They allow the forecaster to get a sense of the distribution of ensemble forecasts for one or a few contour values
3) Small distances between contours usually indicate small uncertainty
4) They allow the forecaster to see if there is more than one likely solution

Answer 6

2, 3, 4

Question 7

True or False? If none of the precipitation types is forecast by a majority of the ensemble members, the dominant precipitation type is not defined.

Answer 7

False

Question 8

What is the most plausible interpretation of the trough forecast in this idealized mean and spread product?

Choose the best answer.

1) There is a relatively large uncertainty regarding its strength/depth
2) There is a relatively large uncertainty regarding its location
3) There is relatively large uncertainty regarding its existence
4) There is a small cluster of forecasts different from the ensemble mean

Answer 8

2

Question 9

True or False? A forecaster can use a mean and spread diagram to determine which contour value to choose for a spaghetti diagram.

Answer 9

True

Question 10

Consider this idealized graphic of ensemble mean and spread for 12-hour accumulated precipitation. Which of the following statements about this graphic are true? Note the abbreviations for the different zones in the region shown (NW for northwest, NC for north central, etc).

Choose all that apply.

1) The spread is largest in the NC region
2) The spread is largest in the SC and Ctr regions
3) The greatest potential for 12-hour precipitation exceeding 1.5” is in the NC region
4) The greatest potential for 12-hour precipitation exceeding 1.5” is in the Ctr and SC regions

Answer 10

2, 4

Question 11

True or False? A plume diagram for temperature can show multiple solutions for the timing of a cold frontal passage through a model grid box

Answer 11

True

Question 12

In the box and whisker diagram presented, which of these statements is true about the 00 UTC 19 November 2001 ensemble forecast valid at 12 UTC on 20 November?

Choose all that apply.

1) The box indicates that half the ensemble members ranged from about 11 degrees C to 13 degrees C
2) The whiskers indicate that there are more members with temperatures below 11 degrees C than above
3) The red dot indicates that half the ensemble members were within approximately 1 deg C of each other
4) The box and whisker diagram indicates that most ensemble members fell below the median value

Answer 12

1, 3

Question 13

Buoyancy is a force acting on a parcel of air in response to a difference in ____ causing an air parcel to accelerate ____.

Answer 13

density | vertically

Question 14

What are the factors that intend to increase buoyancy?

Answer 14

Higher water vapor

Higher potential temperature

Question 15

What steps in the convective process take place immediately following the point in the thunderstorm lifecycle depicted in the graphic?

Answer 15

Parcels spread laterally and create the cloud anvil

Parcels reach their equilibrium level

Question 16

As shown in this thermodynamic diagram, an unsaturated air parcel follows a ____ adiabat up to the ____ then follows a ___ adiabat up to the ____

Answer 16

dry | LCL | moist | EL

Question 17

The Lifted Index characterizes the amount of instability by lifting a parcel from the surface to ____ mb. A negative LI indicates ____ buoyancy while a positive LI indicates ____ buoyancy.

Answer 17

500 | positive | negative

Question 18

True or False?
CAPE is a measure of the potential energy in the atmosphere and generally can be used as a measure of the potential strength of convective updrafts.

Answer 18

True

Question 19

The amount of CAPE in the atmosphere is most influenced by the vertical distribution of ____ and ____

Answer 19

buoyancy | moisture

Question 20

Which sounding is more likely to produce a stronger updraft and why?

Answer 20

Sounding A because CAPE is concentrated in the lower half allowing parcel to accelerate more quickly and reducing entrainment and precipitation loading.

Question 21

Which sounding is more likely to produce a stronger downdraft and why?

Answer 21

Sounding B because dry midlevels will result in evaporation of precipitation and subsequent cooling that will enhance downdrafts

Question 22

Convective Inhibition (CIN) is a measure of a ___, which can prevent an air parcel from reaching its ____, thereby preventing convection from occurring.

Answer 22

Capping inversion | LFC

Question 23

CIN can be reduced or eliminated by which of the following mechanisms in the lower atmosphere?

Answer 23

Synoptic scale ascent
Moistening
Heating

Question 24

Which of the following are the primary contributors to downdraft strength?

Answer 24

Evaporation

Precipitation loading

Question 25

Which of the above soundings (right or left panel) would result in a stronger downdraft? Why?

Answer 25

Left panel because midlevels are drier, resulting in more evaporation, cooling, and downward acceleration.

Question 26

_____ dominate(s) early in an ordinary cell’s life cycle and ____ dominate(s) in the later stages

Answer 26

Updrafts | downdrafts

Question 27

True or False?

When vertical wind shear is strong, buoyancy processes are the dominant control on convective updrafts and downdrafts.

Answer 27

False

Question 28

True or False? For a given amount of shear, a stronger, more buoyant updraft will not tilt as much as a weaker updraft.

Answer 28

True

Question 29

A sheared vertical wind profile leads to which of the following?

Answer 29

Horizontal vorticity in the atmosphere

Updraft tilt

Question 30

The strength and organization of boundary-layer-based MCSs _____ with higher vertical wind shear magnitudes

Answer 30

increases

Question 31

How does vertical wind shear influence storm organization?

Answer 31

By enhancing the ability of a thunderstorm cold pool to trigger new storms

Question 32

In this graphic, which side is downshear?

Answer 32

Right (Cell 5)

Question 33

Wind shear profiles with clockwise curvature, common in the Great Plains are responsible for producing which kind of supercell?

Answer 33

Dominant-right-moving supercells

Question 34

As a rule of thumb, the optimal state for cold pool lifting occurs when the propagation speed of the of cold pool roughly equals the difference between the surface wind and the wind at what level?

Answer 34

2.5 km AGL

Question 35

At midlatitudes, how much low-level shear is necessary to significantly enhance cold pool lifting and cell regeneration?

Answer 35

15 m/s over the lowest 2.5 km AGL

Question 36

When the updraft column blocks the environmental flow, it creates a dynamic affect of relative _____ of the updraft.

Answer 36

high pressure upshear and low pressure downshear

Question 37

Along the edge of a cold pool, a strong jet of vertical motion results when what conditions are satisfied?

Answer 37

Regions of positive and negative horizontal voriticty equal magnitude and size exist in close proximity to each other

Question 38

How much wind shear is necessary to initiate squall lines?

Answer 38

There is no minimum

Question 39

While bow echo and supercell environments have much overlap, supercells tend to have ____

Answer 39

a deeper shear profile (at least 4-6 km AGL)

Question 40

How much wind shear is typically necessary for supercell formation?

Answer 40

Greater than 25 m/s over the lowest 4-6 km AGL

Question 41

When estimating the shear environment of a squall line, that component of the low-level environmental shear oriented _____ to the line exerts the most control on the line’s structure and evolution.

Answer 41

perpendicular

Question 42

On which side of a cold pool is deep lifting enhanced?

Answer 42

Downshear side