Special Wind Shear Group

METEOROLOGY FLIGHT PLANNING

CHAPTER ONE

As with METARs, TAF sky conditions will consist of five or six characters. The first two or

three letters indicate the amount of sky coverage, from Figure 1-20, above, and the last three

digits indicate the height of the cloud bases in hundreds of feet AGL.

The types of clouds will not be forecast with the exception of cumulonimbus (CB), which will

always be given as a separate layer (e.g., SCT005CB). In the event of a partial obscuration, it

will be considered the first cloud layer and reported as FEW000, SCT000, or BKN000.

Special Wind Shear Group

An entry such as "WS020/22030KT" indicates the presence of wind shear. The three digits

before the slash indicate the altitude (AGL), and the characters following the slash indicate wind

direction and speed. North American stations will insert this special non-convective wind shear

group immediately after the cloud group when it is forecast for altitudes 2000 feet AGL and

below. However, if it cannot be forecast with accuracy, a less specific format of "WSCONDS"

(wind shear conditions) may be used, and no further numeric data will be given. If no wind shear

is forecast, then this group is omitted.

Icing Group

This group consists of six numbers only and begins with a "6." It is used to forecast non-

thunderstorm icing (the presence of thunderstorms implies moderate or greater icing), and is

repeated as often as necessary to indicate multiple icing layers. The group is omitted if no icing

is forecasted. The following example illustrates the decoding of the icing group: 641104

The "6" indicates that icing is forecasted. The next digit, "4," is the type of forecasted icing from

Figure 1-26 (moderate icing). If more than one type of icing is forecast within the same stratum

of air, the highest code figure, the most severe, will be used. The next three digits, "110,"

indicate the height of the base of the icing stratum in hundreds of feet AGL, which is 11,000 feet

AGL in this case. If the numbers "000" are used, this would indicate icing occurring at or below

100 feet AGL. The last digit, "4," is the thickness of the icing layer in thousands of feet (4000

feet here) using numbers 1 through 9. If layer is thicker than 9000 feet, the icing group is

repeated so that the base of the repeated group coincides with the top of the first encoded icing

group. If multiple layers not related to each other are forecasted, the layers are encoded in an

ascending order.

AVIATION ROUTINE WEATHER REPORTS AND TERMINAL AERODROME

FORECASTS 1-21