Content:

1. Forecasting Process

2. Printed Weather Reports

3. Printed Weather Forecasts

4. Severe Weather Reports and Forecasts

1. Forecasting Process

• The Forecasting Process:

• Observation

• Communication

• Processing

• Dissemination

• Forecasting Accuracy and Limitations

• Predictions of weather occurring within 12 hours or less are the most accurate

• Major daily weather changes can be predicted with relative accuracy up to 48 hours in advance

• Weather events such as large storms or major heat waves can be accurately forecast up to five days in advance

• Forecasters can do a fairly good job of estimating the average precipitation and temperatures up to 10 days ahead

• Generally, espected temperatures and precipitation predictions in monthly and seasonal forecasts are based only on statistical probability

• Forecasting Methods:

• Presistence forecasts

• Trend forecasts

• Climatological forecasts

• Analogue forecasts

• Meteorological forecasts

• Numerical weather predictions

2. Printed Weather Reports

• Aviation Routine Weather Report (METAR) - an observation of surface weather reported in a standard format

• Report Type:

• METAR - issued every hour

• SPECI - issued to report a change in one or more elements

• Station Identifier

• ICAO prefix

• Date and time (UTC or Zulu (Z))

• Modifier

• Wind Information

• Visibility

• Present Weather

1. Intensity or proximity

2. Descriptor

3. Precipitation

4. Obstruction to visibility

5. Any other weather phenomena

• Sky Condition

• Temperature and Dew Point

• Temperature below zero degrees Celsius are prefixed with an M to indicate minus

• Altimeter Setting

• Prefixed by the letter A

• Remarks

• Begins with RMK

• Pilot Weather Report (PIREPs)

• PIREPs confirm such things as:

• Height of bases and tops of cloud layers

• In-flight visibility

• Icing conditions

• Wind shear

• Turbulence

3. Printed Weather Forecasts

• Terminal Aerodrome Forecast (TAF): contains an estimate of possible weather conditions at a specific airport

• Type of Forecast

• None - Routine TAF

• AMD - Amended

• COR - Corrected

• RTD - Delayed

• Location

• Date and time of issue

• The first two numbers of the date and time represent the day of the month, and the next four are the Zulu time that the forecast was issued

• Valid date and time

• TAFs are normally valid for twenty-four or thirty hours unless amended

• The valid period is reported as two four-digit numbers

• Valid period + the hour in Zulu

• Forecast

• The same way as METARs

• Weather, including obstructions to visbility, is added to the forecast only when it is significant to aviation

• Expected visibilities greater than six statute miles are indicated by P

• Low-level wind shear not associated with convective activity and indicated by the letters WS, is followed by the height AGL, a slash, and the wind direction and speed

• Cumulonimbus (CB) is the only cloud type included in a TAF

• Forecast Change Group - indicates that a significant change to the weather condition is expected to endure for the duration of the report time period

• FM - a rapid change is expected within an hour of the indicated time

• BECMG - a gradual change in weather is expected during the indicated time period. If the weather is improving, this code will be followed by NSW, meaning no significant weather

• Temporary Conditions - wind, visibility, weather, or sky conditions that are expected to last less than an hour are described in a temporary (TEMPO) group, which includes the anticipated time period

• Probability Forecast - when the probability of a thunderstorm or precipitation event is less than 50 percent, the TAF includes a probability group, instead of a change or temporary group; the number after PROB shows the percentage of the probability

• The Winds and Temperatures Aloft Forecast (FB Winds)

• An estimate of wind direction in relation to true north

• Wind speed in knots

• Temperature in degrees Celsius for selected altitudes (MSL)

• Each altitude and station has a six or seven digits code representing:

• True direction from which the wind is blowing

• The speed at which the wind is blowing

• The temperatures

• If you see a number larger than 36, the wind speed is greater than 100 knots. Subtract 50 from the first two digits to determine the direction, and add 100 to the second two digits for the wind speed

• A code of 9900 indicates light and variable winds (less than five knots)

4. Severe Weather Reports and Forecasts

• Hurricane Advisories

• A hurricane advisory (WH) provides

• The location of the storm center

• The storm's expected movement

• Maximum winds in and near the storm center

• Minimum pressure in the storm center

• Convective Outlook

• Severe Weather Watch Bulletin: Defines areas of possible severe thunderstorms or tornados