chapter 3- Practical forecasting techniques Flashcards

1
Q

Thickness of a layer of the atmosphere is

A

a measure of how warm or cold the layer is; high values mean warm air, and low values mean cold air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Thickness can be calculated from

A

the heights reported on a radiosonde ascent, or a thermodynamic diagram

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Thickness can be calculated by

A

subtracting the lower (height) value from the upper value, which always gives a positive number

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Suppose 500 hPa height is 5407 m and 1000 hPa height is 23 m, what is the thickness of the layer 500‐1000 hPa?

A

The 500‐1000 hPa layer thickness = 5407 – 23 = 5384 m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

In practical meteorology, the most common layers wherein thickness values are analyzed and forecast are:

A

500‐1000 hPa;

850‐1000 hPa;

700‐1000 hPa;

700‐850hPa

and 500‐700 hPa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

The 500‐1000 hPa thickness also known as the

A

‘total’ thickness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

The 500‐1000 hPa thickness also known as the ‘total’ thickness, is used to

A

define the broad average temperature for the lower half of the troposphere.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

850‐1000 hPa:

A

This is useful for defining the temperature structure in the lowest 1500 m or so of the atmosphere, and can therefore be used in such things as rain/snow prediction, maximum temperature forecasting etc.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

700‐1000 hPa:

A

Similar to 500‐1000 hPa but focused more on the lowest 3 km of the atmosphere, the layers nearer the earth’s surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

500‐700 hPa/700‐850 hPa:

A

Used in studies of differential thermal advection, particularly when considering possible convection, degrees of instability etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

The use of 850‐1000 hPa thickness to forecast the

A

potential daytime maximum temperature has long been recognized

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

The use of 850‐1000 hPa thickness to forecast the potential daytime maximum temperature has long been recognized. For example

A

the relationship between 850‐1000 hPa thickness (h*) and the unadjusted maximum temperature (Tu), obtained for regions south of England, is:
Tu =‐192.65 + 0.156h*

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

For example, the relationship between 850‐1000 hPa thickness (h*) and the unadjusted maximum temperature (Tu), obtained for regions south of England, is:
Tu =‐192.65 + 0.156h*
An adjustment is then

A

added to this figure (Tu), depending upon forecast ‘cloud class’ and the time of the year.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

The four cloud classes are:

A
  • Class 0: Low and medium cloud generally less than half cover. High cloud not overcast. Fog only around dawn, if at all.
  • Class 1: Roughly 50% cloudiness. If fog occurs, it clears slowly during the morning.
  • Class 2: Mainly cloudy. If fog occurs, clears by midday, but slowly.
  • Class 3: Mainly cloudy. If fog occurs, clears by midday, but slowly.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

The empirical equation for forecasting maximum temperature (TMax) from 850‐1000 hPa thickness is of the form:

A

y=a+bx

where

y- Predictand, the variable whose value is to be predicted (e.g., TMax) and

x- Predictor, the variable whose value is used for prediction (e.g., 850‐1000 hPa thickness)

a- intercept

b- slope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

The slope and intercept are estimated from

A

the historical data

17
Q

The hypsometric equation tells us that

A

the thickness of a pressure layer is proportional to the mean temperature of that layer.

18
Q

The hypsometric equation tells us that the thickness of a pressure layer is proportional to the mean temperature of that layer.
Thus,

A

an empirical relationship can be derived between the thickness of pressure layers and the occurrence of rain, snow, and freezing precipitation

19
Q

Hank’s Rain‐Snow Relationship

A

It is an empirical rain‐snow relationship based on the 1000‐700 mb thickness

20
Q

Hank’s Rain‐Snow Relationship

It is an empirical rain‐snow relationship based on the 1000‐700 mb thickness.
In this relationship,

A

a critical thickness value of 2480 m (for 1000‐700 mb layer) has been used to separate rain from snow effectively.

21
Q

That is, if the thickness of 1000‐700 mb layer is:

A
  • Less than 2480 m –mostly snow can be expected
  • Greater than 2480 m –mostly rain can be expected
  • Equal to 2480 m – 50% snow and 50% rain can be expected
22
Q

That is, if the thickness of 1000‐700 mb layer is:
• Less than 2480 m –mostly snow can be expected
• Greater than 2480 m –mostly rain can be expected
• Equal to 2480 m – 50% snow and 50% rain can be expected
It is to be noted that

A

we need moisture and lift to produce precipitation. Thus, thickness values alone just provide a clue to the precipitation type, not the occurrence of the precipitation.

23
Q

Rain‐snow Relationship

24
Q

It is to be noted that

A

there will be some variation of these values with elevation. Essentially, as the elevation increase, the critical thickness value for rain versus snow also increases.

25
Freezing Rain ‐Snow Relationships Freezing rain and sleet (ice pellets) require
the presence of a warmer than freezing layer above the colder than freezing layer near the earth's surface.
26
Freezing rain and sleet (ice pellets) require the presence of a warmer than freezing layer above the colder than freezing layer near the earth's surface. Thickness can be used to
approximate this warm‐over‐cold requirement. Specifically, the warm layer can be represented with the 850‐700 mb thickness and the cold layer with the 1000‐850 mb thickness.
27
The table shows the relative values to forecast freezing precipitation.
Thus, the type of precipitation can be determined from the thicknesses of the 850‐700 mb and 1000‐850 mb layers, and the surface temperature.