Valid Time

CHAPTER TWO

METEOROLOGY FLIGHT PLANNING

Valid Time

The computer constructs the Winds-Aloft Prognostic Charts based on observed winds and

temperatures recorded at a particular valid time. Figure 2-20 shows four panels with enlarged

legends for easier viewing. These charts represent forecast winds and temperatures for a specific

time, rather than a period of time. Since wind speeds generally change slowly in the upper

atmosphere, these winds and temperatures are considered to be representative forecast averages

until the next set of charts is received. Therefore, the information shown is theoretically accurate

for the valid time of the chart only.

Figure 2-21 Legend of Winds-Aloft Prognostic Charts

209.

WINDS-ALOFT FORECASTS

Winds-Aloft Forecasts are teletype forecasts of upper winds and temperatures for selected

stations within the continental United States (Figure 2-21). They are transmitted twice a day and

the teletype identifier "FD" appears in the heading. Additionally, they are broken into two

segments. Each segment gives a valid time and a for-use time (the forecast period) at the

beginning of each segment; the total forecast is usable for a period of 15 hours. The forecast

represents conditions both as they should occur specifically at the valid time and also the average

conditions as they should occur during the for-use time.

2-22 DATA DISPLAYED ON WEATHER IMAGERY PRODUCTS