Chapter 10 — WATCH ROUTINES 



planning of aircraft landing and taking off from 

 an air base. The code is based on the National 

 Weather Service AVIATION FORECAST (TER- 

 MINAL) code and generally employs the same 

 abbreviations and form used in the airways 

 hourly observation code to be found in FMH 

 No. 1, Surface Observations. The PLATF sym- 

 bolic code form is as follows: 



G1G1G2G2 h s h s NWww ddff (Plain language) QNH 



The time group indicates the 24-hour per- 

 iod of the terminal forecast. 



The heights of cloud bases are indicated in 

 hundreds of feet above the ground. Between the 

 surface and 5,000 feet, heights are expressed 

 to the nearest 100 feet; intervals of 1,000 feet 

 from 5,000 feet to 25,000 feet, and intervals 

 of 5,000 feet above 25,000 feet. The heights of 

 cloud bases and cloud layers include surface 

 based obscuring phenomena such as heavy snow, 

 smoke, or fog which are expected to restrict 

 the vertical visibility to less than the height 

 of the base of the lowest cloud layer. (Refer 

 to FMH No. 1 on reporting of obscured sky). 



Cloud layers are written in ascending order 

 of height separated by a space (scattered 

 1/10-5/10) (broken 6/10-9/10) and (overcast 

 10/10). Surface based obscuring phenomena, such 

 as snow, smoke, or fog that is expected to 

 reduce the vertical visibility to less than the 

 height of the lowest layer of cloud is indicated 

 by the symbol X and the height is the forecast 

 vertical visibility. The term variable (V) is 

 used in the remarks section when two or more 

 cloud conditions are expected alternately. The 

 predominant or most general cloud cover con- 

 dition is included in the main text and the 

 variable condition listed in the remarks. The 

 base of the lowest layer of clouds forecast 

 to have more than five-tenths coverage con- 

 stitutes the ceiling. Where two or more layers 

 of scattered clouds are forecast even though 

 their cumulative amount is ten- tenths, the sky 

 is considered as scattered. The rule of sum- 

 mation used in observations does not apply. 

 The C identifier for celling is not used by 

 Naval Weather Service forecasters. 



The visibility term follows the cloud cover 

 and is reported in miles or increments of 

 miles. The visibility Is forecast in the same 

 values as prescribed in FMH No. 1. The term 

 "variable" is not used in describing visibility 



in the general conditions group. The condi- 

 tions that may be variable are described in 

 remarks. 



Standard letters or abbreviations contained 

 in FMH No. 1 are used to indicate the state 

 of weather or obstructions to vision and follow 

 the visibility figure without a space. Intensities 

 are denoted by a plus sign (+) for heavy, minus 

 sign (-) for light, and a double minus for very 

 light. Thunderstorms are carried as T. If the 

 visibility is forecast to be 6 miles or less, 

 weather or obstruction to vision must be in- 

 cluded. 



The surface wind group follows the terms 

 for weather and obstructions to visibility and 

 is forecast when the wind is expected to be 

 5 knots or more. If the wind is forecast less 

 than 5 knots the abbreviation C for clam is 

 used. Wind is separated by one space from the 

 previous group. The wind is reported in the 

 direction from which the wind is blowing meas- 

 ured clockwise from true north. Speed is fore- 

 cast in knots. Wind direction is written in 

 degrees to the nearest 10-degree increment. 

 Gust winds are identified by the letter G 

 following the wind speed. 



Meteorological conditions considered to be 

 of importance and not adequately covered in the 

 general group are carried in the remarks sec- 

 tion using authorized contractions and abbre- 

 viations where possible. Modifying remarks 

 normally apply to visibility, sky cover, or 

 winds. The following terms may apply in de- 

 fining the changeable weather conditions: 



1. Gradually (GRADU). This term indicates 

 an improving or deteriorating condition dur- 

 ing a specific period. 



2. Temporary (TEMP). This term is used 

 to modify the general forecast condition when 

 changes are forecast to occur more than once 

 or twice during the forecast period. 



3. Occasional (OCNL). This term is used 

 to modify a general condition with temporary 

 changes occurring no more than once or twice 

 during the forecast period to which the gen- 

 eral condition applied. The changes in question 

 should cover considerably less than half the 

 total time. 



4. Vicinity (VCNTY). This term refers to 

 air mass type weather, such as showers, 



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