Surface Prognosis Charts

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 NDFD Weather Type shows areas of precipitation expected at the valid time of the forecast and are shaded in colors depending on the type and likelihood of precipitation. The areas are derived from the National Weather Service's National Digital Forecast Database (NDFD) grid for weather.

Here are the precipitation types:

NDFD Rain (Chance)	There is chance of measurable rain (≥0.01") at the valid time.
NDFD Rain (Likely)	Measurable rain (≥0.01") is likely at the valid time.
NDFD Snow (Chance)	There is chance of measurable snowfall (≥0.01" liquid equivalent) at the valid time.
NDFD Snow (Likely)	Measurable snow (≥0.01" liquid equivalent) is likely at the valid time.
NDFD Mix (Chance)	There is a chance of measurable mixed precipitation (≥0.01" liquid equivalent) at the valid time. "Mixed" can refer to precipitation where a combination of rain and snow, rain and sleet, or snow and sleet are forecast.
NDFD Mix (Likely)	Measurable mixed precipitation (≥0.01" liquid equivalent) is likely at the valid time. "Mixed" can refer to precipitation where a combination of rain and snow, rain and sleet, or snow and sleet are forecast.
NDFD Ice (Chance)	There is a chance of measurable freezing rain (≥0.01") at the valid time.
NDFD Ice (Likely)	Measurable freezing rain (≥0.01") is likely at the valid time.
NDFD T-Storm (Severe)	The potential exists for some storms to reach severe levels at the valid time.

Weather Depiction Plots

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.