COMET Modules Flashcards
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
1, 2, 3
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
1, 2, 3, 4
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
1, 3, 4
True or False? One of the biggest challenges in using EPS forecasts is interpreting the post-processed EPS output.
True
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.
small-scale
larger-scale
better than
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
2, 3, 4
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.
False
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
2
True or False? A forecaster can use a mean and spread diagram to determine which contour value to choose for a spaghetti diagram.
True
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
2, 4
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
True
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
1, 3
Buoyancy is a force acting on a parcel of air in response to a difference in ____ causing an air parcel to accelerate ____.
density | vertically
What are the factors that intend to increase buoyancy?
Higher water vapor
Higher potential temperature
What steps in the convective process take place immediately following the point in the thunderstorm lifecycle depicted in the graphic?
Parcels spread laterally and create the cloud anvil
Parcels reach their equilibrium level
As shown in this thermodynamic diagram, an unsaturated air parcel follows a ____ adiabat up to the ____ then follows a ___ adiabat up to the ____
dry | LCL | moist | EL
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.
500 | positive | negative
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.
True
The amount of CAPE in the atmosphere is most influenced by the vertical distribution of ____ and ____
buoyancy | moisture
Which sounding is more likely to produce a stronger updraft and why?
Sounding A because CAPE is concentrated in the lower half allowing parcel to accelerate more quickly and reducing entrainment and precipitation loading.
Which sounding is more likely to produce a stronger downdraft and why?
Sounding B because dry midlevels will result in evaporation of precipitation and subsequent cooling that will enhance downdrafts
Convective Inhibition (CIN) is a measure of a ___, which can prevent an air parcel from reaching its ____, thereby preventing convection from occurring.
Capping inversion | LFC
CIN can be reduced or eliminated by which of the following mechanisms in the lower atmosphere?
Synoptic scale ascent
Moistening
Heating
Which of the following are the primary contributors to downdraft strength?
Evaporation
Precipitation loading
Which of the above soundings (right or left panel) would result in a stronger downdraft? Why?
Left panel because midlevels are drier, resulting in more evaporation, cooling, and downward acceleration.
_____ dominate(s) early in an ordinary cell’s life cycle and ____ dominate(s) in the later stages
Updrafts | downdrafts
True or False?
When vertical wind shear is strong, buoyancy processes are the dominant control on convective updrafts and downdrafts.
False
True or False? For a given amount of shear, a stronger, more buoyant updraft will not tilt as much as a weaker updraft.
True
A sheared vertical wind profile leads to which of the following?
Horizontal vorticity in the atmosphere
Updraft tilt
The strength and organization of boundary-layer-based MCSs _____ with higher vertical wind shear magnitudes
increases
How does vertical wind shear influence storm organization?
By enhancing the ability of a thunderstorm cold pool to trigger new storms
In this graphic, which side is downshear?
Right (Cell 5)
Wind shear profiles with clockwise curvature, common in the Great Plains are responsible for producing which kind of supercell?
Dominant-right-moving supercells
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?
2.5 km AGL
At midlatitudes, how much low-level shear is necessary to significantly enhance cold pool lifting and cell regeneration?
15 m/s over the lowest 2.5 km AGL
When the updraft column blocks the environmental flow, it creates a dynamic affect of relative _____ of the updraft.
high pressure upshear and low pressure downshear
Along the edge of a cold pool, a strong jet of vertical motion results when what conditions are satisfied?
Regions of positive and negative horizontal voriticty equal magnitude and size exist in close proximity to each other
How much wind shear is necessary to initiate squall lines?
There is no minimum
While bow echo and supercell environments have much overlap, supercells tend to have ____
a deeper shear profile (at least 4-6 km AGL)
How much wind shear is typically necessary for supercell formation?
Greater than 25 m/s over the lowest 4-6 km AGL
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.
perpendicular
On which side of a cold pool is deep lifting enhanced?
Downshear side
