Model Products FAQ

What do the pointed ends of some colorscales mean?

The ends of the colorscale indicate whether values beyond the colorscale are shaded. For instance, on CAPE/CIN charts, CAPE is not shaded for values below 500 J/kg, so that end of the colorscale is flat. Values greater than 3750 J/kg are all shaded with the same color; ie., 3750-4000 J/kg will be the same as 4000-4250 J/kg.

What does "3-stage dashed" mean? Why are some dashed lines thicker than others on thermal / thickness plots?

On most thermal / thickness plots, the dashed lines follow a cyclical pattern of widths to make comparing two adjacent isolines easier. For instance, if the 5460dam line is thin and the interval is 60dam:

  • 5280dam: width-1 thin
  • 5340dam: width-2 medium
  • 5400dam: width-3 thick
  • 5460dam: width-1 thin
  • 5520dam: width-2 medium
  • 5580dam: width-3 thick
  • 5640dam: width-1 thin

In general, a medium line is warmer than the adjacent thin line; a thick line is warmer than the adjacent medium line; and a thin line is warmer than the adjacent thick line. In the attached example, for instance, cooler air is to the northwest.

What do the B+ / B- buttons do?

These buttons change both runtime and forecast offset in such a way that the valid time is maintained. On NAM products, for instance, B- moves the runtime back 6 hours while moving the forecast offset up 6 hours.

Meteogram FAQ

What are the colored bars and black triangles on the meteogram?

These represent B/E groups, such as RAB37SNE43. When present, each row represents a precipitation type. Each triangle points away from when the precipitation was happening; that is, a triangle marking a beginning time points leftward and a triangle marking an ending time points rightward. The leftmost triangle will always be labelled with precipitation type and either B (beginning) or E (ending).

Note that the actual time being marked by a triangle is given by the position of its hypotenuse, not its tip.

In the example below (from Pittsburgh on 2018 November 15), we can infer the following:
  • Ice pellets fell from around 2130Z to 2345Z.
  • Freezing rain ended around 2230Z. There is no prior FZRAB in the selected span.
  • Snow fell continuously from around 1100Z to 1900Z.
  • Snow fell intermittently from around 1900Z to 2205Z. There is no posterior SNE in the selected span.

What is on the cloud height graph?

This is a logarithmic plot of cloud heights. The letters have the following meanings:
  • F: Few clouds
  • S: Scattered clouds
  • B: Broken cover
  • O: Overcast
  • V: Vertical visibility obstructed
  • C: Clear (CLR reported; not rendered if CLR is missing)
  • A: Automated observation (clouds above 12,000 feet may not be reported)
  • R: Corrected observation

What is the grey table at the bottom of the meteogram?

This table contains additional information not otherwise plotted on the meteogram:
  • Vis: Horizontal visbility in nautical miles.
  • Ceil: Cloud ceiling; the level of lowest BKN, OVC, or VV layer. A dash "-" means that there is no cloud ceiling. Units are hundreds of feet or hundreds of meters, whichever is plotted on the cloud levels graph.
  • Pcp<1: Hundredths of inches of liquid-equivalent precipitation since the last standard hourly observation - that is, the Pxxxx group. T indicates a trace.
  • Pcp 6: Hundredths of inches of liquid-equivalent precipitation in either the last 3 hours (at 03Z, 09Z, 15Z, or 21Z) or the last 6 hours (at 00Z, 06Z, 12Z, or 18Z) - that is, the 6xxxx group. T indicates a trace.
  • Ice<1: As in Pcp<1, but for icing accumulation (I1xxx group).
  • Ice 6: As in Pcp 6, but for icing accumulation (I3xxx and I6xxx groups).
  • SnoDp: Inches of snow depth (4/xxx group).
  • Tmn 6: Minimum temperature over the past 6 hours (1xxxx group). Units are Celsius or Fahrenheit, whichever is plotted on the temperature / dewpoint grpah.
  • Tmx 6: Maximum temperature over the past 6 hours (2xxxx group). Units are Celsius or Fahrenheit, whichever is plotted on the temperature / dewpoint grpah.