Online Ground School (Private Pilot)
Lesson 13.5: Weather Charts
Weather charts are used to show the overall view of the U.S. current or forecast weather. These charts show fronts and major weather systems as the move across the counter. There are three types of charts used, they are:
Surface Analysis Chart
Weather Depiction Chart
Surface Analysis Charts
This charts show the current surface weather such as high and low pressure, fronts, temperature, dew point, wind direction and speed, etc. These three charts are issued every three hours and cover the lower 48 states.
Weather Depiction Charts
They show the surface conditions derived from the METARs. These charts are issued every three hours starting at 0100Z. Weather depiction charts also shows areas of IFR, VFR, and MVFR (Marginal VFR) along with fronts, troughs, and squall lines.
IFR – Ceiling less than 1,000 feet with visibility less than 3 miles.
VFR – Ceiling greater than 3,000 feet or clear skies with visibility more than 5 miles.
MVFR – Ceilings 1,000 – 3,000 feet with visibility 3 – 5 miles.
These can be seen in two different ways, one is low-level form the surface up to FL240 (24,000 feet) and the other is high-level from FL250 – FL630 (25,000 - 63,000 feet). The low-level Prognostic chart is the primary chart to help brief the VFR pilots.
They are issued four times a day 0000Z, 0600Z, 1200Z and 1800Z. The Prognostic Charts are used to show freezing levels, turbulence, and low cloud ceilings or restricted visibly by area of MVFR and or IFR conditions.