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CHAPTER 4

LIMITED SURFACE OBSERVATION

SECTION I.

TABLES FOR LIMITED OBSERVATIONS

4-1. General

a. With the new equipment and weaponry, meteorological needs of the US Army have increased significantly over the past 10 years. Systems such as Copperhead, multiple-launch rocket system, remotely piloted vehicle, Firefinder, and meteorological data system AN/TMQ-31 will all require increased met support.

b. The responsibility to provide surface and upper air weather observations in the area forward of division command elements for Army artillery, engineers, intelligence, aviation, and medical units has always been placed on the US Army.

c. The mission of the field artillery meteorology section has been expanded to include taking and recording a limited surface observation. To assist the US Army FA meteorology crew member in taking this surface observation, the supplementary surface weather report (SUPREP) code has been adopted. The SUPREP is a standard NATO code developed to be used by nonweather people, usually with little or no weather observing equipment and with only limited weather training.

d. The artillery limited surface observation will be taken at a time which is compatible with the section's schedule for upper air soundings. These messages will be disseminated in accordance with FM 6-15, paragraph 3-7. Requests for additional observations will be coordinated with the meteorology technician.

e. It is understood that in some areas of the code, additional information may seem repetitious. Cloud information and surface winds, for example, both have additional amplification groups. Because of varied weather requirements of the many new systems, both identified and anticipated, only surf data will be considered an optional group.

4-2. SUPREP Code (Symbolic Breakdown)

The message will be transmitted in six-digit groups. The order of groups must be maintained. Only the 99 group (inclosed in brackets below) will be considered optional and may be omitted if not applicable. If an element within a group cannot be reported, it must be entered as a slash (/). The symbols of the code and order of transmittal are listed below. A series of tables explaining the code follows.

SUPRP

Code identifier (indicated SUPREP met message to follow).

Q

Octant of the globe. Same as artillery met.

LaLaLa

Latitude (tenths of degrees). Same as artillery met.

LoLoLo

Longitude (tenths of degrees). Same as artillery met.

Note: When a coded location is desirable, the Q, latitude, and longitude will be an arbitrary number of digits to specify position (must be understood by receiving unit).

YY

Day of month Greenwich mean time (GMT). Same as artillery met.

GGgg

Time of observation (hours and minutes, GMT).

Na

Total amount of cloud cover (table 4-1).

D

Direction of surface wind (table 4-2).

F

Force of surface wind (table 4-3).

V

Visibility at surface (table 4-4).

w

Present weather (table 4-5).

A'

Amplification of phenomenon reported by w (table 4-6).

HHH

Height of station (in tens of meters).

R

State of road in vicinity of the observation point (table 4-7).

T

State of terrain prevailing in the vicinity of the observation point (table 4-8).

A

State of water surface (table 4-9).

TT

Air temperature in whole degrees Celsius (negative temperatures are encoded by adding 50 to the absolute value of the temperature; e.g. -20 is encoded as 70).

PPPP

Pressure at the observation point (encode to tenths of a millibar; thousands digits of millibars are omitted).

dd

Direction (in tens of degrees) from which surface wind is blowing (two digits). This group will be reported as 99 when the wind speed is less than 5 knots.

ff

Wind speed in knots (two digits).

Nh

Amount of cloud reported at height ha (table 4-10).

ha

Height of lowest cloud layer observation point (table 4-11).

[99]

Indicator for surf data (when applicable).

[Hs]

Average height of breakers in meters (table 4-12).

[Ps]

Period of breakers in seconds (table 4-13).

[Dw]

Direction of wave's approach to beach with observer's back to the sea (table 4-14).

[Ws]

Width of surf zone in meters (table 4-15).

4-3. Tables

A series of tables is above. These tables are used with the SUPREP code. They give an explanation of the code for each weather element to be reported by the observer. The tables help the observer determine what symbol to report.

SECTION II.

INSTRUCTIONS FOR TAKING SURFACE WEATHER OBSERVATIONS

4-4. Message Identifier

Use the five-letter SUPREP identifier followed by octant of globe for the first six-letter/number group.

4-5. Station Location

In the second six-number group, three numbers are for latitude and three are for longitude to a tenth of a degree. When the location must be coded, the code is on agreement with the receiving and transmitting units.

4-6. Date and Time

Both are given in Greenwich mean time (GMT) in hours and minutes at time of observation.

4-7. Sky Condition

Of all the weather conditions that adversely affect aircraft/flying operations, low clouds and low visibility are by far the most common. This paragraph decribes the method of observing the sky conditions

a. General. Sky condition observations consist of two elements:

(1) The amount of clouds or obscuration present.

(2) Remarks about the sky condition in the area that would be helpful to the weather forecaster or to the aviator.

b. Sky Cover Amounts (Na).

(1) The total amount of the sky covered by clouds or an obscuration can be described by using one of the following words:

(a) Clear: Less than one-eighth of the sky is covered by clouds.

(b) Scattered: One-eighth to less than one-half of the sky is covered (approximately 10-50%).

(c) Broken: One-half or more of the sky is covered (approximately 60-90%).

(d) Overcast: Sky is totally coverd by clouds or obscuring phenomena (e.g., fog, blowing snow, blowing sand, or smoke).

(2) Determine the total cloud amount by considering the sky above you as a celestial dome and mentally dividing it into eight equal parts. For example, you are the observer standing at point X in figure 4-1. There are three different cloud layers in the sky above you. Here you have 7/8 cloud cover, but the cirrus and the altocumulus overlap by about 1/8, so you would report total cloud amount as 6/8, or a broken condition.

(3) Very often, significant features of the sky cover cannot be explained simply by scattered, broken, etc. Explanations for hilly or mountainous stations are included in the code and must be used. These codes, which are extremely important to aircraft operations, are:

 

Code

Description

 

3-Scattered

(Hills in clouds)

 

6-Broken

(Hills in clouds)

 

8-Overcast

(Hills in clouds)

4-8. Wind Direction and Speed

Wind speed and direction are necessary in forecasting weather, especially in locations where weather is often associated with frontal systems. Wind direction and speed can be used to locate these fronts and to determine their movement. Frequently, the combination of wind direction and terrain produces significant variation in wind speed over very short distances. Local variations in wind speed can also produce deviations from the normal in weather conditions.

a. Direction (D). Wind direction is defined as the direction from which the wind is blowing. Wind may be taken from a direct reading of the hand-held anemometer ML-433. Use of the ML-433 is covered in FM 6-15.

b. Speed (F). Wind speed may also be read from a direct reading of the hand-held anemometer ML-433. If no wind equipment is available, the speed may be estimated by using the following:

4-9. Visibility (V)

Visibility is an important limiting factor in flying operations. Poor visibility restricts visual surveillance and flying observations.

a. Visibility is the greatest distance an object can be seen and identified by the normal eye, without the aid of optical devices such as binoculars and starlight scopes.

In actual practice, visibility is the greatest distance that prominent objects such as trees, buildings, water towers, or natural landmarks (hills) can be seen clearly enough to be identified.

b. In daytime, any building, water tower, telephone pole, road, hill, clump of trees, etc., that can be seen under ideal conditions may be used as a visibility marker if the distance to the object is known.

c. At night, the above objects can be used if their silhouettes can be identified. However, the best nighttime marker is an unfocused light as a known distance from the observation point. (This does not include searchlights, airport rotating beacons, or automobile headlights aimed directly at you.)

d. The visibility that is reported must be representative of at least half of the horizon circle. In making this determination, the horizon circle is normally divided into quadrants as shown in figure 4-2. Any two quadrants (they need not be continuous) may be used to determine the prevailing visibility. Visibility is reported in meters, to the nearest hundred meters, as listed in table 4-4.

e. Quadrant visibility may be reported as a remark at the end of the observation. If you feel that the visibility in one quadrant is significantly different from the prevailing visibility, you should include a remark. For example: Visibility N, meters. Any quadrant or direction may be used for this remark.

4-10. Weather and Obstructions to Vision (w)

We have already mentioned the important effect visibility has on operations. It would not be logical to report a reduction in visibility without describing it in terms of the weather phenomena upon which the visibility depends. These weather phenomena are divided into two main groups: weather and obstructions to vision. They are dicussed separately in detail in the following paragraphs.

a. Obstructions to vision are as follows:

(1) Smoke: Fine ash particles suspended in the air. When smoke is present, the disk of the sun appears very red at sunset and sunrise and has a reddish tinge throughout the day. Smoke at a distance, such as from a forest fire, usually has light grayish or bluish color.

(2) Haze: Dust and other material too small to be seen individually by the unaided eye. Haze reduces visibility and resembles a uniform veil over the landscape that subdues the colors. Haze appears bluish against a dark background but dirty or orange against a bright background such as the sun. In contrast, fog appears grayish and feels damp on the skin.

(3) Fog: Very small drops of water suspended in the air which reduce the visibility.

(4) Blowing sand or dust: Dust or sand raised by the wind to such an extent that the visibility is impaired.

(5) Blowing snow: No appreciable amount of falling snow, but snow from the ground is carried into the air by the wind and the visibility is reduced.

b. Weather types are as follows:

(1) Precipitation: Precipitation includes all forms of moisture that fall to the earth's surface, such as rain, snow, and hail. All forms of precipitation can be classified as liquid, freezing, or frozen. Of special importance are the freezing types of precipitation, which present a great hazard to aviation.

(a) Liquid precipitation:

1. Drizzle - very small water droplets which seem almost to float in the air and visibly follow air motion. Drizzle falls from fog or very low clouds.

2. Rain - precipitation which reaches the earth's surface as relatively large drops. Rain can be classed as light, moderate, or heavy, depending upon the rate of fall.

(b) Freezing precipitation:

1. Freezing rain - precipitation in the form of very cold raindrops, a portion of which freezes and forms a smooth coating of ice upon striking an exposed surface.

2. Freezing drizzle - precipitation in the form of very cold drizzle which freezes in the same manner as freezing rain.

(c) Frozen precipitation.

1. Ice pellets - frozen raindrops formed by rain falling through a layer of cold air. Ice pellets may adhere to any exposed surface, forming an uneven layer of ice.

2. Hail - precipation in the form of balls or irregular lumps of ice. Hail results when water drops are repeatedly carried aloft to the colder air by the violent air currents usually associated with thunderstorms.

3. Snow - precipitation composed of ice crystals.

4. Snow grains - small grains of snow which are soft and opaque and lack the six-sided appearance of the ordinary snowflake.

(2) Thunderstorms: Thunder is heard at your location. A thunderstorm may or may not be accompanied by rain or hail.

(3) Tornado: A circular whirl, or wind of great velocity and small horizontal diameter. The horizontal diameter of a tornado varies from a few feet up to a mile, and the wind speeds often exceed 200 mph. Tornadoes are short lived, usually not lasting more than an hour or two. If a tornado is sighted, call your reporting station immediately and give its location and direction of movement. Speed in reporting your sighting is of the utmost importance to all concerned. Tornadoes are extremely rare in western Germany.

c. Amplification of phenomena reported by the code w, as represented in table 4-6, (A'), is self-explanatory.

d. Height of observation point/station above mean sea level (HHH) is given in decimeters.

4-11. State of Road in Vicinity of Observation Point (R)

Extract the appropriate figure from table 4-7.

4-12. State of Terrain in Vicinity of Observation Point (T)

Extract the appropriate figure from table 4-8.

4-13. Temperature (TT)

Enter in whole degrees Celsius. Negative temperatures are encoded by adding to the absolute value of the temperature; e.g., -20 is coded as 70.

4-14. Pressure (PPPP)

The surface pressure to the nearest tenth of a millibar is encoded. When pressure is over 1000 millibars, the thousand digit is dropped.

4-15. Wind Direction (dd)

In this portion of the code, the wind direction (in tens of degrees) is reported in two digits. This data is used to further amplify wind information reported in the fourth six-digit group (i.e., D and F). These two digits will be encoded as 99 when the wind speed is less than 5 knots.

4-16. Wind Speed (ff)

The wind speed is reported in knots and in two digits.

4-17. Amount of Low Cloud (Nh)

The lowest cloud is determined for the amount of cover in eighths. For encoding, see table 4-10.

4-18. Height of Low Cloud (ha)

The height of the lowest cloud above the observing point is estimated. For encoding see table 4-11.

4-19. Indicator for Surf Data (99)

a. When the unit is located at a seacoast area, it is important to give surf conditions. The 99 group indicates that surf data will follow. The surf data includes average height of breakers, time breakers last, direction of waves' approach to beach, and the width of the surf zone. For estimation and encoding of these variables, see tables 4-12, 4-13, 4-14, and 4-15.

b. When surf data is not available, the message will end with height of low cloud plus any remarks on weather elements that might seem appropriate. Thus, the message includes seven six-digit groups when surf data is not included. Any data or weather element that is missing is represesented by a slash (/).

4-20. Plain Language Remarks

a. Any remark that the observer considers beneficial or explanatory may be listed at the bottom of the message. Examples:

(1) The direction of a thunderstorm from your location and the approximate direction it is moving toward; e.g., Thunderstorms E moving NE.

(2) The direction of lightning from your location; e.g., Lightning overhead and SW through NW.

(3) Obscuring phenomena at a distance from your location but not occurring at your location; e.g., Fog bank NE through SE.

b. These are just a few examples. In other words, any remark that you feel might be helpful to a military operation may be included as long as that remark pertains to current weather.

4-21. DA Form 5033-R Limited Surface Observation

Figure 4-3 is a DA Form to be completed for each limited surface observation. Local reproduction of this form is authorized.



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