MOS_NAM Meteogram for Washington DC
This is a 60 hour forecast time series for a particular surface reporting station location. The data plotted include temperatures, winds, pressure, clouds and present weather. These plots are updated once every 12 hours at around 12:45 EST. The plot is divided up into several subplots described top to bottom:
Temperature and dewpoint chart - This shows temperature as the top line and dewpoint as the bottom line.
EXTT (extreme temperature) - The maximum and minimum temperatures are plotted below the chart at specific reporting times. 12Z and 18Z are generally low temperatures and 0Z and 6Z are high temperatures.
WX (present weather data) - This shows the weather being reported at that time as a weather symbol.
SNWDP (snow depth) - This shows forecasted snow fall in inches for the previous 12 hours. A value of 1 indicated anywhere from a Trace to 2 inches. A value of 2 indicates snowfall of 2 to 4 inches. A value of 4 indicates 4 to 6 inches and 6 means more than 6 inches.
PREC (precipitation) - This shows precipitation totals in inches. The values are 24 hour totals generally at 12Z, 6 hour totals at 0Z, 6Z and 18Z, 3 hour totals elsewhere.
VIS (visibility) - This shows the horizontal visibility in miles.
WIND (winds and cloud cover) - This is the standard wind and cloud cover symbols used in the surface data plots. Up is north.
Cloud chart - This chart gives cloud layer information. The vertical axis is height of cloud base in feet and is logarithmic. The layers are plotted as horizontal lines. Clear skies are plotted as a 'C'. Scattered cloud layers (1/8th to 3/8th coverage) are plotted as a single short dash. Broken cloud layers (4/8th to 7/8th coverage) are plotted as two short dashes. Overcast layers are plotted as a single long dash. The actual cloud ceiling is displayed below the chart in 100s of feet if the ceiling is below 10,000 feet.
Pressure chart - This chart plots sea level pressure (or altimeter setting if pressure not reported) in millibars. This may not be available for all sites.
Time - This is the reporting time in universal time.