Decoding Guide

Surface Prognosis Charts

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Abstract:
Three charts (Fronts/Pressure, Precipitation, and WxDepict) indicating forecasted frontal boundaries, precipitation, and IFR or MVFR flying conditions.

Description:
These products contain a combination of three NWS plots: the forecast Fronts chart, the Low-Level Weather Depiction chart, and the Instantaneous Precipitation chart. The forecast Fronts chart depicts the manually forecast position of surface fronts, troughs, squall lines, lows, and highs. The Weather Depiction chart depicts the forecasts of the expected low-level weather. Cloud coverage, ceiling, and visibility are included in the description. The Instantaneous Precipitation chart depicts the manually forecast instantaneous precipitation expected at the valid time.

Issuance:
0000, 0600, 1200 and 1800 UTC (Weather Depiction)
0000 and 1200 UTC (forecast Fronts & Instantaneous Precipitation)

Data Sources:
Surface and upper air analysis, weather depiction analysis, radar and satellite data, computer models

Depiction:
The forecast front location portion of the product shows expected front locations and high and low pressure centers. The location of forecasted fronts are shown using standard front symbology. High and Low pressure centers are depicted using and symbols. Pressure appears close to the symbol and is given in mb. Generally, add a prefix of 9 if the plotted pressure value is greater than 50 and a prefix of 10 if the plotted value is less than 50.

The Instantaneous Precipitation portion of the product, colored in green, shows the forecasted precipitation coverage. Areas of expected precip are outlined by solid lines and may or may not be shaded. A standard precipitation symbol is associated with the enclosed area. The shading indicates the coverage of precipitation. In the case of convective precipitation (thunderstorms), the shading indicates coverage greater than 50%. For non-convective precipitation, shading indicates continuous precip.

Examples:

	Area of forecasted convective (thunderstorm) precipitation with coverage < 50%.
	Area of forecasted convective (thunderstorm) precipitation with coverage > 50%.
	Area of forecasted intermittent stratiform (non-convective) precipitation
	Area of forecasted continuous stratiform (non-convective) precipitation

Weather Depiction Plots

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The Weather Depiction plot depicts areas of expected IFR and/or marginal VFR (MVFR) flying conditions. Scalloped lines indicate MVFR conditions (ceilings 1000-3000ft visibility 3-5). Solid lines indicate IFR conditions (ceilings below 1000ft and visibility < 3 miles). The jagged lines indicate the Freezing Level at the surface and the dashed lines indicate the Freezing Level above Mean Sea Level.

Examples:

	MVFR conditions -- Ceiling expected between 1,000 and 3,000 ft and/or visibility between 3 and 5 miles
	IFR conditions -- Ceiling expected to be below 1000 ft and/or visibility below 3 miles.
	Freezing Level at the surface.
	Freezing Level above Mean Sea Level.