December 1999 10-1 Section 10
WINDS AND TEMPERATURES ALOFT CHARTS Winds aloft charts, both forecast and observed, are computer-generated products. The forecast winds aloft charts also contain forecast temperatures aloft.
FORECAST WINDS AND TEMPERATURES ALOFT (FD) Forecast winds and temperatures aloft (FD) charts are prepared for eight levels on eight separate panels.
The levels are 6,000; 9,000; 12,000; 18,000; 24,000; 30,000; 34,000; and 39,000 feet MSL. They are available daily, and the 12-hour progs are valid at 1200Z and 0000Z. A legend on each panel shows the valid time and the level of the panel. Levels below 18,000 feet are in true altitude, and levels 18,000 feet and above are in pressure altitude. Figure 10-1 shows examples from a winds and temperatures aloft forecast chart. Figure 10-2 provides a closer view of the winds and temperature aloft forecast chart. Temperature is in whole degrees Celsius for each forecast point and is entered above and to the right of the station circle. Arrows with pennants and barbs, similar to those used on the surface map, show wind direction and speed. Wind direction is drawn to the nearest 10 degrees with the second digit of the coded direction entered at the outer end of the arrow. To determine wind direction, obtain the general direction from the arrow, and then use the digit to determine the direction to the nearest 10 degrees. For example, a wind in the northwest quadrant with a digit of “3” indicates 330 degrees. A calm or light and variable wind is shown by “99” entered to the lower left of the station circle. See Table 10-1 for examples of plotted temperatures and winds with their interpretations.
December 1999 10-2 Table 10-1 Plotted Winds and Temperatures Plotted Interpretation 12 6 3 6 0 5 -09 6 6 -47 -11 99 12 degrees Celsius, wind 060 degrees at 5 knots 3 degrees Celsius, wind 160 degrees at 25 knots 0 degrees Celsius, wind 250 degrees at 15 knots -9 degrees Celsius, wind 260 degrees at 50 knots -47 degrees Celsius, wind 360 degrees at 115 knots -11 degrees Celsius, wind calm or light and variable
December 1999 10-3
OBSERVED WINDS ALOFT Charts of observed winds for selected levels are sent twice daily on a four-panel chart valid at 1200Z and 0000Z. The chart depicts winds and temperatures at the second standard level, 14,000, 24,000, and 34,000 feet. Figure 10-3 is an example of this chart, and Figure 10-4 is an example of one of the panels. Wind direction and speed are shown by arrows, the same as on the forecast charts. A calm or light and variable wind is shown as “LV” and a missing wind as “M,” both plotted to the lower right of the station circle. The station circle is filled in when the reported temperature/dew point spread is 5 degrees Celsius or less. Observed temperatures are included on the upper two panels of this chart (24,000 feet and 34,000 feet). A dotted bracket around the temperature means a calculated temperature.
The second standard level (Figure 10-3) for a reporting station is found between 1,000 and 2,000 feet above the surface, depending on the station elevation. The second standard level is used to determine low-level wind shear and frictional effects on lower atmosphere winds. To compute the second standard level, find the next thousand-foot level above the station elevation and add 1,000 feet to that level. For example, the next thousand-foot level above Oklahoma City, OK, (station elevation 1,290 feet MSL) is 2,000 feet MSL. The second standard level for Oklahoma City, OK, (2,000 feet + 1,000 feet) is 3,000 feet MSL or 1,710 feet AGL.
For example:
Station:
Amarillo, TX Bismarck, ND Topeka, KS Key West, FL Station elevation:
3,604 MSL 1,677 MSL 879 MSL 0 MSL Next thousand-foot level above station:
4,000 MSL 2,000 MSL 1,000 MSL 1,000 MSL +1,000 +1,000 +1,000 +1,000 _________ _________ _________ _________ Second standard level:
5,000 MSL 3,000 MSL 2,000 MSL 2,000 MSL or or or or 1,396 AGL 1,323 AGL 1,121 AGL 2,000 AGL Note that the 12,000 foot MSL panel is true altitude, while the 24,000 and 34,000 feet MSL panels are in pressure altitude. (See Figure 10-1.)
USING THE CHARTS The use of the winds aloft chart is to determine winds at a proposed flight altitude or to select the best altitude for a proposed flight. Temperatures also can be determined from the forecast charts.
Interpolation must be used to determine winds and temperatures at a level between charts and data when the time period is other than the valid time of the chart.
December 1999 10-4 Forecast winds are generally preferable to observed winds since they are more relevant to flight time.
Although observed winds are 5 to 8 hours old when received, they still can be a useful reference to check for gross errors on the 12-hour prog.
INTERNATIONAL FLIGHTS Computer-generated forecast charts of winds and temperatures aloft are available for international flights at specified levels. The U.S. National Centers of Environmental Prediction (NCEP), near Washington D.C., is a component of the World Area Forecast System (WAFS). NCEP is designated in the WAFS as both a World Area Forecast Center and a Regional Area Forecast Center (RAFC). Its main function as a World Area Forecast Center is to prepare global forecasts in grid-point form of upper winds and upper air temperatures and to supply the forecasts to associated RAFCs. One of NCEP’s main RAFC functions is to prepare and supply to users charts of forecast winds, temperatures, and significant weather.
For example, Figures 10-5 and 10-6, are originated by NCEP. The flight level of Figure 10-5 is 34,000 feet MSL, and Figure 10-6 is 45,000 feet MSL. This, along with the valid time of the chart and the data base time (data from which the forecast was derived), makes up the legend along an edge of each chart.
Forecast winds are expressed in knots for spot locations with directions and speed depicted in the same manner as the U.S. forecast winds and temperatures aloft chart (Figure 10-1). Forecast temperatures are depicted for spot locations inside circles that are expressed in degrees Celsius. For charts with flight levels (FL) at or below FL180 (18,000 feet), temperatures are depicted as negative (-) or positive (+). On charts for FLs above FL180, temperatures are always negative and no sign is depicted.
December 1999 N095 12HR UPPER WIND PROG D16 NO95 12HR UPRER WIND PROG D166 600OFT WINDS. AND TEMP
• NOAA/HWS/NCEP WASHIN Figure 10-1. Forecast Winds and Temperatures Aloft Chart.
10-5
December 1999 N095 12HR UPPER WIND PROG D184 39000FT WINDS AND TEMPS 12Z TAL JAN 8 1998 VALID · Figure 10-2. Panels from Forecast Winds and Temperatures Aloft Chart.
-57 NO95 12HA UPPER NIND PROG D169 34000FT NINDS AND TEMPS YALID 12Z THU JAN 8 1998 -55 10-6
December 1999 34000 FT: (250MB) 12Z NED JAN 7 1998 AVN PREPBUFR WINDS AND TEMPS 4000 FT. (600MB) WINDS 12Z NED JAN AYN PREPBUFR WINDS NOAA/NWS/NCEP WASHINGTON Figure 10-3. Observed Winds and Temperatures Aloft Chart.
24000 FT. (400MB) 12Z WED JAN 7 1998 AVN PREPBUFR WINDS AND TEMPS 2D STANDARDILYL ABOVE SFC 12Z WED JAN 7 1998 AYN PREPEUFR WINDS OBS.
WINDS ALOFT OBS D142.. N106. DATAL CUTOFF 2+40 10-7
December 1999 25 AYN PREPEUFR WiNDS AND TeMPS 24000 FT: (400MB) OBS. 12Z VED JAN 7 1998 Figure 10-4. Panel from Observed Winds and Temperatures Aloft Chart.
36 10-8
December 1999 11-1 Section 11
SIGNIFICANT WEATHER PROGNOSTIC CHARTS Significant weather prognostic charts (progs) (Figure 11-1) portray forecasts of selected weather conditions at specified valid times. Each valid time is the time at which the forecast conditions are expected to occur. Forecasts are made from a comprehensive set of observed weather conditions. The observed conditions are extended forward in time and become forecasts by considering atmospheric and environmental processes. Forecasts are made for various periods of time. A 12-hour prog is a forecast of conditions which has a valid time 12 hours after the observed data base time, thus a 12-hour forecast. A 24-hour prog is a 24-hour forecast, and so on. For example, a 12-hour forecast based on 00Z observations is valid at 12Z. Altitude information on the prog charts is referenced to mean sea level (MSL) and compatible with aviation. Altitudes below 18,000 feet are true altitudes while above 18,000 feet are pressure altitudes or flight levels (FL). The prog charts for the conterminous United States are generated for two general time periods. Day 1 progs are forecasts for the first 24-hour period. Day 2 progs are forecasts for the second 24-hour period. Day 1 prog charts are prepared for two altitude references in the atmosphere. Forecast information for the surface to 24,000 feet is provided by the lowlevel significant weather prog chart. Forecast information from above 24,000 to 60,000 feet is provided by the high-level significant weather prog chart. The day 2 prog chart is prepared without regard to altitude and is provided by the 36- and 48-hour surface prog chart.
U.S. LOW-LEVEL SIGNIFICANT WEATHER (SIG WX) PROG The low-level significant weather prog chart (Figure 11-1) is a day 1 forecast of significant weather for the conterminous United States. Weather information provided pertains to the layer from surface to FL240 (400 mbs.) The information is provided for two forecast periods, 12 hours and 24 hours. The chart is composed of four panels. The two lower panels depict the 12- and 24-hour surface progs that are produced at Hydrometeorolgical Prediction Center (HPC) in Camp Springs, Maryland. The two upper panels depict the 12- and 24-hour significant weather progs that are produced at the Aviation Weather Center (AWC) in Kansas City, Missouri. The chart is issued four times a day; and the observation data base times for each issuance are 00Z, 06Z, 12Z, and 18Z.
SURFACE PROG PANELS The surface prog panels display forecast positions and characteristics of pressure systems, fronts, and precipitation.
Surface Pressure Systems Surface pressure systems are depicted by pressure centers, troughs, and, on selected panels, isobars.
High and low pressure centers are identified by "Hs" and "Ls" respectively. The central pressure of each center is specified. Pressure troughs are identified by long dashed lines and labeled "TROF." Isobars are shown on selected panels. Isobars are drawn as solid lines and portray pressure patterns. The value of each isobar is identified by a two-digit code placed on each isobar. Isobars are drawn with intervals of 8 mbs relative to the 1,000 mb isobar. Note that this interval is larger than the 4-mb interval used on the surface analysis chart. The 8-mb interval provides a less sensitive analysis of pressure patterns than the 4-mb interval. Occasionally, nonstandard isobars will be drawn using 4-mb intervals to highlight patterns with weak pressure gradients. Nonstandard isobars are drawn as dashed lines. Examples of standard isobars drawn are the 992; 1,000; and 1,008 mb isobars.
December 1999 11-2 Fronts Surface fronts are depicted on each panel. Formats used are the standard symbols and three-digit characterization code used on the surface analysis chart. (See Section 5.)
Precipitation Solid lines enclose precipitation areas. Symbols specify the forms and types of precipitation. (See Table
11-1.) A mix of precipitation is indicated by the use of two pertinent symbols separated by a slash.
Identifying symbols are positioned within or adjacent to the precipitation areas. Precipitation conditions are described further by the use of shading. Stable precipitation events are classified as continuous or intermittent. Continuous precipitation is a dominant and widespread event and, therefore, shaded.
Intermittent precipitation is a periodic and patchy event and unshaded. Shading is also used to characterize the coverage of unstable precipitation events. Areas with more than half coverage are shaded, and half or less coverage are unshaded. (See Table 11-2.) A bold dashed line is used to separate precipitation with contrasting characteristics within an outlined area. For example, a dashed line would be used to separate an area of snow from an area of rain.
December 1999 11-3 Table 11-1 Standard Weather Symbols Moderate turbulence Rain shower Severe turbulence Snow Shower Moderate icing Thunderstorm Severe icing Freezing rain Rain Tropical storm Snow Drizzle Hurricane (Typhoon)
December 1999 11-4 Table 11-2 Significant Weather Prog Symbols Intermittent snow Rain showers covering half or less the area Continuous rain Rain showers and thunderstorms covering more than half the area
SIGNIFICANT WEATHER PANELS The significant weather panels display forecast weather flying categories, freezing levels, and turbulence for the layer surface to FL240. A legend on the chart illustrates symbols and criteria used for these conditions. (See Figure 11-1.)
Weather Flying Categories The weather flying categories are visual flight rules (VFR), marginal VFR (MVFR), and instrument flight rules (IFR). Ceiling and visibility criteria used for each category are the same as used for the weather depiction chart. (See Section 6.) IFR areas are enclosed by solid lines. MVFR areas are enclosed by scalloped lines. All other areas are VFR.
Freezing Levels The surface freezing level is depicted by a zigzag line and labeled "SFC." The surface freezing level separates above-freezing from below-freezing temperatures at the Earth's surface. Freezing levels aloft are depicted by thin, short dashed lines. Lines are drawn at 4,000-foot intervals beginning at 4,000 feet and labeled in hundreds of feet. For example, "80" identifies the 8,000-foot contour. Freezing level heights are referenced to MSL. The lines are discontinued where they intersect corresponding altitudes of the Rocky Mountains. The freezing level values for locations between lines is determined by linear interpolation. For example, the freezing level midway between the 4,000 and 8,000 foot lines is 6,000 feet. Areas with forecast multiple freezing levels have lines drawn to the highest freezing level. For example, with freezing levels forecast at 2,000, 6,000, and 8,000 feet, the analysis is drawn to the 8,000 foot value. Notice that not all freezing levels are identified with a multiple freezing level event.
Information about the 2,000- and 6,000-foot freezing levels in this example would not be displayed.
Surface-based multiple freezing levels are located over areas which have below-freezing temperatures at the surface and above-freezing temperatures within at least one layer aloft. Freezing rain and freezing drizzle (freezing precipitation) are associated with surface-based multiple freezing levels. The