Forecasting weather elements and phenomena

Question 1

Maximum temperatures usually occur at about

Answer 1

2 P.M. or 3 P.M

Question 2

while minimum temperatures occur

Answer 2

around sunrise or just after sunrise. (6 A.M.)

Question 3

To determine tomorrow’s maximum temperature

Answer 3

examine today’s 2 P.M. or 3 P.M. surface map. Calculate, using ½ the speed of the 500 MB winds the parcel of air that will be influencing your area 24 hours later. The temperatures in that parcel will very closely resemble tomorrow’s maximum temperature in your area.

Question 4

To determine tomorrow’s maximum temperature, examine today’s 2 P.M. or 3 P.M. surface map. Calculate, using ½ the speed of the 500 MB winds the parcel of air that will be influencing your area 24 hours later. The temperatures in that parcel will very closely resemble tomorrow’s maximum temperature in your area. …………………….. must be studied and then introduced into each forecast.

Answer 4

Local variations

Question 5

Since the 500 MB winds are from the

Answer 5

southwest at 50 kts

Question 6

Since the 500 MB winds are from the southwest at 50 kts. weather which is now ………………………….. will influence our area tomorrow at ………

Answer 6

600 miles (1/2 50 X 24 hours) to our southwest

3 p.m.

Question 7

Since the 500 MB winds are from the southwest at 50 kts. weather which is now 600 miles (1/2 50 X 24 hours) to our southwest will influence our area tomorrow at 3 p.m. Since most of the upstream temperatures are in

Answer 7

the upper 60’s, temperatures in the upper 60’s are likely for the forecast area the next day.

Question 8

The procedure for minimum temperatures is

Answer 8

exactly the same as for maximum temperatures with one exception. Instead of using a 3 P.M. surface map, the 6 A.M. or 7 A.M. surface map should be used. Employ the same upstream procedures and introduce the local variations experienced in your area.

Question 9

If an increase in clouds, moisture or wind is expected in the parcel of air being transported into your area,

Answer 9

certain modifications must be made.

Question 10

If an increase in clouds, moisture or wind is expected in the parcel of air being transported into your area, certain modifications must be made. Generally speaking, any or all of these will tend to

Answer 10

to lower the maximum temperature expected as well as raise the minimum temperature expected

Question 11

Morning cloud cover can be very

Answer 11

misleading

Question 12

Morning cloud cover can be very misleading. For example,

Answer 12

“upstream” weather may indicate overcast skies at all reporting Stations causing a forecaster to “lower” his estimate on forecasted maximum temperatures.

Question 13

Morning cloud cover can be very misleading. For example, “upstream” weather may indicate overcast skies at all reporting

Stations causing a forecaster to “lower” his estimate on forecasted maximum temperatures. However, upon investigation,

Answer 13

the forecaster may notice that the HEIGHT of these clouds is below 1000 feet

Question 14

Morning cloud cover can be very misleading. For example, “upstream” weather may indicate overcast skies at all reporting

Stations causing a forecaster to “lower” his estimate on forecasted maximum temperatures. However, upon investigation, the forecaster may notice that the HEIGHT of these clouds is below 1000 feet. These ………. clouds, probably ………….

Answer 14

low clouds, probably stratus, will most likely “burn off” by mid morning, thus not preventing temperatures from reaching the expected maximum.

Question 15

These low clouds, probably stratus, will most likely “burn off” by mid morning, thus not preventing temperatures from reaching the expected maximum. However,

Answer 15

, if these low clouds have a higher deck of clouds above them (two or more decks) the sun will probably not be able to penetrate. Overcast skies will persist all day. Lower maximum temperatures can thus be expected.

Question 16

The above factors, yes or no, when and how much can usually be determined very accurately for the

Answer 16

next 12 hours by using the surface map along with the 500 mb

Question 17

the figure indicates that

Answer 17

the 500 MB. winds indicate the rain area will effect station “A”. In fact, light rain (..) should move into the area in approximately six 6 hours. (150 miles divided by 25 MPH). However, the rain should become moderate (…) and heavy (….) after about four (4) hours. (100 miles divided by 25kts) of light rain. Moderate and heavy rain should continue for about 4 hours, tapering off to very light rain showers, then ending.

Station “B” would not be affected by this rain pattern, since all the rain would be passing to the north of the area.

Question 18

RAIN, YES OR NO, WHEN AND HOW MUCH?

Here are some factors that may complicate matters:

Answer 18

1.A MOVING 500 MB. TROUGH

2.A “LIFTING OUT” TROUGH

3.A “DIGGING” TROUGH

4.A DEVELOPING STORM

Question 19

this will work if

Answer 19

the trough is stationary

Question 20

The example given above works well if the trough is stationary. However, if

Answer 20

the trough is moving, modifications must be introduced.

Question 21

The example given above works well if the trough is stationary. However, if the trough is moving, modifications must be introduced. We must use

Answer 21

vectors

Question 22

The example given above works well if the trough is stationary. However, if the trough is moving, modifications must be introduced. We must use vectors.

The rain pattern will move according to the

Answer 22

“resultant of the two vectors, the vectors being 1) direction of the upper air winds plus 2) the eastward movement of the trough

Question 23

The faster the trough is moving, the

Answer 23

greater the eastward component will be in the resultant vector showing the actual movement of precipitation, taking the trough movement into account

Question 24

The STRONGEST WINDS are

Answer 24

“digging” down the western side of the trough.

Question 25

. The STRONGEST WINDS are “digging” down the western side of the trough. Since the winds are weak at the “bottom” of the trough, this trough will

Answer 25

DEEPEN AND MOVE SOUTH-EASTWARD VERY SLOWLY, IF IT MOVES AT ALL. WE CALL THIS A “DIGGING TROUGH”.

Question 26

Answer 26

the trough in the central part of the United States with the STRONGEST WINDS AT THE BOTTOM OF THE TROUGH. This trough will REMAIN ABOUT THE SAME IN INTENSITY BUT WILL MOVE EASTWARD

Question 27

Answer 27

shows the trough in the center of the United States with the **_STRONGEST WINDS MOVING UP THE EASTERN SIDE OF THE TROUGH**_. This trough will _**weaken and move rapidly towards the NORTHEAST_**.

Question 28

A "LIFTING OUT" TROUGH

Answer 28

When a trough is lifting out, the area of precipitation, along with the intensity of the precipitation, generally DECREASES

Question 29

When a trough is lifting out, the area of precipitation, along with the intensity of the precipitation, generally DECREASES. This should be taken into account when determining

Answer 29

when precipitation will start, how much will fall, and when it will end.

Question 30

**.****_A "DIGGING" TROUGH_** When a trough is "digging"

Answer 30

the area of precipitation, along with the intensity of the precipitation generally **_INCREASES_**. This again must be considered when making a forecast.

Question 31

A DEVELOPING STORM

Answer 31

If rapid storm development (cyclogenesis) is expected, the size of the precipitation area, as well as the precipitation intensities, will increase significantly

Question 32

If rapid storm development (cyclogenesis) is expected, the size of the precipitation area, as well as the precipitation intensities, will increase significantly. This data should then be

Answer 32

utilized in modifying amounts and duration of precipitation expected.

Question 33

**.****_STORM INTENSIFICATION:_** Certain conditions favor rapid storm intensification. A few are given below:

Answer 33

1. COLD AIR AT THE 500 MB. LEVEL 2. **_VORTICITY:_** 3. COLD AIR ADVECTION AT THE 700 MB. & 500 MB. LEVEL 4. THE "DIGGING" TROUGH -\> 5. DIVERGENCE AT THE 200 MB. LEVEL \> 6. BAROCLINICITY AT THE SURFACE 7. THE JET STREAM AND ITS INFLUENCE ON STORM DEVELOPMENT

Question 34

**_COLD AIR AT THE 500 MB. LEVEL:_** Storms intensify rapidly if

Answer 34

the trough (short wave or long wave) possesses cold air.

Question 35

Storms intensify rapidly if the trough (short wave or long wave) possesses cold air. Generally, a temperature of .................. at the southern extremity of the supporting trough is sufficient for rapid intensification on the surface.

Answer 35

-25°C to -30°C

Question 36

Generally speaking, the colder the air at the 500 MB. level, the

Answer 36

greater the potential for storm deepening

Question 37

Storm deepening is usually favored where

Answer 37

500 MB. CYCLONIC WINDSHEAR & CURVATURE EXIST.

Question 38

Storm deepening is usually favored where 500 MB. CYCLONIC WINDSHEAR & CURVATURE EXIST. These are the components of

Answer 38

POSITIVE VORTICITY

Question 39

A storm developing near station "A" would

Answer 39

deepen rapidly.

Question 40

A storm developing near station "A" would deepen rapidly. 500 MB. wind speeds to the east of “A” are -\>

Answer 40

100 Kts

Question 41

while to the west of “A” near the center of the trough, they are

Answer 41

only 25 Kts

Question 42

A storm developing near station "A" would deepen rapidly. 500 MB. wind speeds to the east of “A” are 100 Kts. while to the west of “A” near the center of the trough, they are only 25 Kts. This creates a

Answer 42

counterclockwise (cyclonic) wind shear

Question 43

A storm developing near station "A" would deepen rapidly. 500 MB. wind speeds to the east of “A” are 100 Kts. while to the west of “A” near the center of the trough, they are only 25 Kts. This creates a counterclockwise (cyclonic) wind shear. The directional curvature at the bottom of the trough

Answer 43

also induces cyclonic wind shear.

Question 44

A storm developing near station "A" would deepen rapidly. 500 MB. wind speeds to the east of “A” are 100 Kts. while to the west of “A” near the center of the trough, they are only 25 Kts. This creates a counterclockwise (cyclonic) wind shear. The directional curvature at the bottom of the trough also induces cyclonic wind shear. Cyclonic wind shear then is

Answer 44

a combination of directional shear and speed shear

Question 45

Cyclonic wind shear then is a combination of directional shear and speed shear. This total shear induces

Answer 45

rotational motion or circulation

Question 46

Cyclonic wind shear then is a combination of directional shear and speed shear. This total shear induces rotational motion or circulation. This is commonly referred to by the meteorologist as

Answer 46

vorticity

Question 47

The greater the shear, the

Answer 47

greater the vorticity.

Question 48

STRONG VORTICITY INDUCES

Answer 48

INDUCESSTRONG SURFACE CYCLOGENESIS

Question 49

STRONG VORTICITY INDUCESSTRONG SURFACE CYCLOGENESIS. Therefore,

Answer 49

troughs with very cold air and strong vorticity possess the greatest potential for explosive surface storm development

Question 50

**_COLD AIR ADVECTION AT THE 700 MB. & 500 MB. LEVEL:_** Since a trough is a pocket of

Answer 50

cold air

Question 51

Since a trough is a pocket of cold air, deepening of the trough will occur if

Answer 51

more cold air is fed into it.

Question 52

STRONG COLD AIR ADVECTION causes

Answer 52

rapid intensification of the trough

Question 53

STRONG COLD AIR ADVECTION causes rapid intensification of the trough. This, in turn, often triggers

Answer 53

rapid surface intensification east of the trough axis.

Question 54

STRONG COLD AIR ADVECTION causes rapid intensification of the trough. This, in turn, often triggers rapid surface intensification east of the trough axis. Generally,

Answer 54

2 or 3 isotherms (less than 60 miles apart) perpendicular to winds stronger than 50 Kts. on the 500 MB. map would be considered favorable for rapid surface cyclogenesis (STORM FORMATION.) \*THE SAME RULES APPLY TO COLD AIR ADVECTION ON THE'

Question 55

When winds on the western side of the trough are strong and from the north or northwest, trough

Answer 55

deepening can be expected

Question 56

When winds on the western side of the trough are strong and from the north or northwest, trough deepening can be expected. (Especially if

Answer 56

weak winds prevail at the base of the trough.)

Question 57

When winds on the western side of the trough are strong and from the north or northwest, trough deepening can be expected. (Especially if weak winds prevail at the base of the trough.) This, in turn, often creates

Answer 57

surface cyclogenesis.

Question 58

Surface storms deepen rapidly when

Answer 58

**_DIVERGENCE_** is present at the 200 MB. level (approximately 38,000 ft.)

Question 59

DELTA EFFECT

Answer 59

divergence is indicated in areas where the contour lines diverge or SPREAD APART

Question 60

The greater the divergence, the

Answer 60

greater the storm deepening.

Question 61

Earlier we mentioned that storms form in zones of strong baroclinicity (strong

Answer 61

temperature gradient).

Question 62

Earlier we mentioned that storms form in zones of strong baroclinicity (strong temperature gradient). Storms may also

Answer 62

deepen under the same conditions.

Question 63

RAPID INTENSIFICATION of a storm can be expected if

Answer 63

very cold and dry air is fed into the storm from the NORTH or NORTHWEST while very warm and humid air is introduced into the storm from the SOUTH OR SOUTHEAST.

Question 64

RAPID INTENSIFICATION of a storm can be expected if very cold and dry air is fed into the storm from the NORTH or NORTHWEST while very warm and humid air is introduced into the storm from the SOUTH OR SOUTHEAST. Of course, favorable support must be present at

Answer 64

500 MB. for any good development to take place.

Question 65

The jet stream may be depicted as a

Answer 65

tube with high wind speeds meandering through the upper atmosphere

Question 66

In order to locate the jet stream it is best to use the

Answer 66

300 MB. map (32,000 ft.) during the summer season and the 200 MB. map (38,000 ft.) during winter.

Question 67

The jet stream often meanders in the general vicinity of

Answer 67

the polar front

Question 68

Wind speeds in the jet stream are

Answer 68

not constant

Question 69

Wind speeds in the jet stream are not constant. Some areas have much higher wind speeds than adjacent locations. Areas having the highest wind speeds are called

Answer 69

VELOCITY MAXIMA

Question 70

Wind speeds in the jet stream are not constant. Some areas have much higher wind speeds than adjacent locations. Areas having the highest wind speeds are called VELOCITY MAXIMA and those showing the lowest speeds are called

Answer 70

calledVELOCITY MINIMA.

Question 71

ISOTACHS

Answer 71

are lines connecting places that have equal wind speeds.

Question 72

Associated with the jet stream is

Answer 72

WIND SHEAR.

Question 73

The air at “A” in Figure 34 is located in an area of

Answer 73

wind shear and is being induced to circulateCOUNTERCLOCKWISE.

Question 74

. The air at “A” in Figure 34 is located in an area of wind shear and is being induced to circulateCOUNTERCLOCKWISE. This occurs

Answer 74

NORTH of the jet stream and is known as CYCLONIC WIND SHEAR

Question 75

The jet stream provides a clue to the

Answer 75

development of lows along the polar front their intensification as well as the location of their associated precipitation.

Question 76

Generally, storms develop and intensify in

Answer 76

AREA I is most favorable because it possesses CYCLONIC WIND SHEAR and alsoCYCLONIC CURVATURE,

Question 77

AREA I is most favorable because it possesses CYCLONIC WIND SHEAR and alsoCYCLONIC CURVATURE, both favorable for

Answer 77

storm development.

Question 78

AREA III,

Answer 78

possesses CYCLONIC CURVATURE, favorable for storm development, BUT it also exhibits ANTICYCLONIC WIND SHEAR, unfavorable for storm development, therefore, strong storm development in AREA III would not be expected.

Question 79

AREA II

Answer 79

is also not a favored area for storm development because although it has **_CYCLONIC WIND**_ _**SHEAR**_, it also has _**ANTICYCLONIC CURVATURE_**.

Question 80

AREA IV

Answer 80

the least likely area for storm development.

Question 81

In summary then, greatest intensification of storms occurs when

Answer 81

the surface storm is located on the eastern edge of a 500 MB. trough, to the left of the jet stream and with a velocity maxima approaching from upstream.

Question 82

The jet stream also influences the

Answer 82

amount of precipitation.

Question 83

The jet stream also influences the amount of precipitation. Generally, the maximum amount of precipitation coincides with

Answer 83

the center of the jet stream

Question 84

The jet stream also influences the amount of precipitation. Generally, the maximum amount of precipitation coincides with the center of the jet stream. Rainfall usually decreases

Answer 84

north and south from this center,

Question 85

The jet stream also influences the amount of precipitation. Generally, the maximum amount of precipitation coincides with the center of the jet stream. Rainfall usually decreases north and south from this center, but much more rapidly on the

Answer 85

south side

Question 86

Storms become more likely in the United States when the jet stream

Answer 86

"digs" deep into the low latitudes, such as it does during the winter.

Question 87

. Storms become more likely in the United States when the jet stream "digs" deep into the low latitudes, such as it does during the winter. During the summer, when the jet stream is usually located

Answer 87

north in Canada, very little storm activity or prolonged rainfall occurs in the continental United States.