*2E Weather - Aviation WX Charts

Question 0

1. Give some examples of current weather charts available at the FSS or NWSO used in flight planning.
   (AC 00-45)

Answer 0

a. Surface analysis chart
b. Weather depiction chart
c. Radar summary chart
d. Short-range surface prognostic chart
e. Significant weather prognostic chart
f. Convective outlook chart
g. Constant pressure analysis chart

Question 1

2. What is a surface analysis chart?

AC 00-45

Answer 1

This is a computer-prepared chart that covers the contiguous 48 states and adjacent areas. The chart is transmitted every three hours. The surface analysis chart provides a ready means of locating pressure systems and fronts. It also gives an overview of winds, temperatures and dew point temperatures at chart time. When using the chart, keep in mind that weather moves and conditions change. Using the surface analysis chart in conjunction with other information gives a more complete weather picture.

Question 2

3. What information does a weather depiction chart provide?

AC 00-45

Answer 2

The weather depiction chart is computer-generated (with a weather observer’s analysis of fronts) from METAR reports. This chart gives a broad overview of the observed flying category conditions at the valid time of the chart. The chart begins at 01Z each day, is transmitted at three-hour intervals, and is valid at the time of the plotted data. The plotted data for each station area are: total sky cover, cloud height or ceiling, weather and obstructions to vision and visibilities. The weather depiction chart is an ideal place to begin in preparing for a weather briefing and flight planning. From this chart one can get a “bird’s-eye” view of areas of favorable and adverse weather conditions at chart time.

Question 3

4. Define the terms: LIFR, IFR, MVFR and VFR.

AIM 7-1-7

Answer 3

LIFR: Low IFR—ceiling less than 500 feet and/or visibility less than 1 mile.
IFR: Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.
MVFR: Marginal VFR—ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.
VFR: Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.

Question 4

5. What are radar summary charts?

AC 00-45

Answer 4

Computer-generated graphical display of a collection of automated radar weather reports (SDs). The chart displays areas of precipitation as well as information about type, intensity, configuration, coverage, echo top, and cell movement of precipitation. Severe weather watches are plotted if they are in effect when the chart is valid. The chart is available hourly with a valid time of 35 minutes past each hour.
This chart aids in preflight planning by identifying general areas and movement of precipitation and/or thunderstorms. Displays drops or ice particles of precipitation size only; it does not display clouds and fog. Therefore, since the absence of echoes does not guarantee clear weather, and cloud tops will most likely be higher than the tops of the precipitation echoes detected by radar, the radar summary chart must be used along with other charts, reports, and forecasts for best effectiveness.

Question 5

6. What are short-range surface prognostic charts?

AC 00-45

Answer 5

Called “progs,” these charts portray forecasts of selected weather conditions at specified valid times (12, 24, 36, and 48 hour progs). Each valid time is the time at which the forecast conditions are expected to occur, 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. Forecast information for the surface to 24,000 feet is provided by the low-level significant weather prog chart. Forecast information from above 24,000 to 60,000 feet is provided by the high-level significant weather prog chart.

Question 6

7. Describe a U.S. low-level significant weather prog chart.
   (AC 00-45)

Answer 6

It is a “Day One” forecast of significant weather for the conterminous U.S., pertaining to the layer from surface to FL240 (400 mb). With 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, and the two upper panels depict the 12- and 24-hour significant weather progs. Issued four times a day at 00Z, 06Z, 12Z, and 18Z. Covered are forecast positions and characteristics of pressure systems, fronts, and precipitation. Much insight can be gained by evaluating the individual fields of pressure patterns, fronts, precipitation, weather flying categories, freezing levels, and turbulence displayed on the chart.

Question 7

8. Describe a mid-level significant weather (SIGWX) chart.

AC 00-45

Answer 7

The mid-level significant weather chart provides a forecast and an overview of significant en route weather phenomena over a range of flight levels from 10,000 feet MSL to FL450, and associated surface weather features. The chart is a “snapshot” of weather expected at the specified valid time and depicts numerous weather elements that can be hazardous to aviation. The AWC issues the 24-hour mid-level significant weather chart four times daily.

Question 8

9. What is a convective outlook chart?

AC 00-45

Answer 8

The convective outlook chart depicts areas forecast to have the potential for severe (tornado, wind gusts 50 knots or greater, or hail 3/4 inch diameter size or greater) and non-severe (general) convection and specific severe weather threats during the following three days. The chart defines areas of slight risk (SLGT), moderate risk (MDT) or high risk (HIGH) of severe thunderstorms for a 24-hour period beginning at 1200 UTC. The Day 1 and Day 2 Convective Outlooks also depict areas of general thunderstorms (GEN TSTMS), while the Day 1, Day 2, and Day 3 Convective Outlooks may use SEE TEXT for areas where convection may approach or slightly exceed severe criteria.

Question 9

10. What are constant pressure analysis charts?

AC 00-45

Answer 9

Any surface of equal pressure in the atmosphere is a constant pressure surface. A constant pressure analysis chart is an upper air weather map where all information depicted is at the specified pressure of the chart. From these charts, a pilot can approximate the observed air temperature, wind, and temperature-dewpoint spread along a proposed route. They also depict highs, lows, troughs, and ridges aloft by the height contour patterns resembling isobars on a surface map. Twice daily, five constant pressure charts are issued from observed data obtained at 00Z and 12Z:
850 mb—5,000 ft
700 mb—10,000 ft
500 mb—18,000 ft
300 mb—30,000 ft
200 mb—39,000 ft