|Condition III||Winds up to 48 knots, wind chill down to -75 degrees, and visibility over 1/4th mile. Unrestricted travel and activity are allowed, but severe weather is possible within 12 hours.|
|Condition II||Winds 48 to 55 knots, wind chill -75 to 100 degrees, or visibility 100 feet to 1/4th mile. Restricted pedestrian traffic only between buildings is allowed. Travel is allowed only on marked trails or roads in authorized, radio-equipped vehicles.|
|Condition I||Winds over 55 knots, wind chill lower than 100 degrees, or visibility less than 100 feet. Severe weather is in progress. All personnel must remain in buildings or the neares shelter.|
* [See figure ³WEATHER3²]
Prior to deep-field put-ins, at least two members of your field team should attend a briefing at the NSFA Weather Office. At this office, you will be instructed in weather observations and how to relay this information to McMurdo. You'll also be issued a meteorological kit that includes a thermometer, an anemometer, an altimeter, and a cloud identification chart. Refer to the booklet in the meteorological kit for in-depth information on field weather observations.
Taking a weather observation entails viewing the meteorological conditions at your camp and reporting those conditions in such a way that they can be visualized by the forecasters at McMurdo. A typical field weather observation in Antarctica relayed by radio includes the following:
1. Wind direction is expressed in degrees (Grid North) and is rounded off to the nearest whole 10 degrees. Refer to Chapter 20: Antarctic Navigation for information on Grid North.
2. Wind speed is expressed in knots/hour. A wind gust is a sudden change in wind speed characterized by a variation of 10 knots between peak and lull. Both the prevailing wind speed and wind gust (if applicable) are reported. An anemometer is used to determine wind speed and direction.
3. Visibility is given in miles; it is dependent on the geographical features near your camp. Ski-way markers, which are set up at known distances, can be used to determine surface visibility. The maximum visibility on a clear day is seven miles, after which a flat ground horizon will fall away to a point that surface conditions cannot be observed.
4. Cloud height is expressed in feet. At an open field, cloud height is estimated. If you are in an area with geographical features of known elevations, use those features to determine cloud height. Cloud heights are reported "Above Ground Level (AGL)." Be able to convert to the "Mean Sea Level (MSL)" if requested.
5. Cloud type and cloud cell appearance will help determine the height of a cloud layer. The atmosphere over the Antarctic is shallower than it is at the equator; therefore, the heights of cloud layers are lower.
Low clouds (stratus and stratocumulus) are commonly found at the surface up to 6,000 feet (MSL).
Mid-level clouds (altostratus and altocumulus) are generally at levels from 6,000 to 12,00 feet (MSL).
High clouds (cirrostratus and cirrus) are usually 12,000 to 16,000 feet (MSL).
6. Cloud coverage is expressed in eighths of the sky. When reporting cloud layers, start at the ground and proceed upward.
|Clear||No clouds present.|
|Scattered||Trace to 4/8ths of the sky covered.|
|Broken||More than 4/8ths, but not total sky coverage.|
|Overcast||Total sky coverage.|
|Partial Obscuration||Sky is partially obscured, typically by snow or blowing snow. Some clouds are discernible.|
|Total Obsuration||Sky is totally obscured, typically by snow or blowing snow.|
|Thin||Layer is transparent.|
|Opaque||Layer is dense.|
7. Temperature is given in degrees Celsius. Make sure that the thermometer is not directly exposed to sunlight. Protect the thermometer from the wind.
8. Pressure is expressed in millibars.
9. Altimeter setting is expressed in inches of mercury to the hundredths. The altimeter setting is the figure that incoming pilots will want the most, because it allows them to determine the altitude (in reference to mean sea level) at which the aircraft will make contact with the landing field.
10. The following surface definition terms should be used to report observations:
|Good||Snow surface features such as sastrugi, drifts, and gullies are easily identified by shadow.|
|Fair||Snow surface features can be identified by contrast. No definite shadows exist.|
|Poor||Snow surface features cannot be readily identified except from close up.|
|Nil||Snow surface features cannot be identified. No shadows or contrast. Dark objects appear to float in the air.|
11. The following horizon definition terms should be used to report observations:
|Good||Horizon is sharply defined by shadow or contrast.|
|Fair||Horizon may be identified, but the contrast between sky and snow surface is not sharply defined.|
|Poor||Horizon is barely discernible.|
|Nil||Total loss of horizon, the snow surface merges with the whiteness of the sky.|
The primary frequencies for passing weather observations are 11553 kHz for remote-site field parties and 4770 kHz for Dry Valley and surrounding areas field parties.