This is a set of contour plots using data from the NAM model. The output fields are consistent with other models so the models can be compared. This model gives forecast information out to 48 hours and plots are sorted 48 hour 4 panel plots where each plot has a panel for the 12, 24, 36 and 48 hour forecast and individual forecast times from initialization to 60 hours in 6 hour increments. These plots are updated once every 12 hours at roughly 11:15 EST.
Sample 850 mb Plot
The 850 mb chart details weather conditions at the 850 mb level or around 5000 feet above sea level. The parameters plotted are temperatures in Celsius (in color contours), heights in white lines and winds plotted as vectors.
850 mb temperature field
The temperature field shows where warm and cold air are located at the 5000 ft level. Temperatures at this level do not show the diurnal temperature changes from morning low to afternoon high we see at the earth's surface so warm and cold air advection can be more easily traced. You can estimate potential afternoon highs from these temperatures by adding: 15C in the summer, 12C in spring and fall, and 9C in the winter and converting to Fahrenheit. For example, if the 850 temp is 4C in summer, the afternoon temperature could reach 4+15=19C=67F. In the winter, 4+9=13C=55F. This algorithm does not work in the western third of the country due to its high altitude.
The 850 temperature is also a decent determiner of the type of precipitation. Since most precipitation forms at 5000 feet or above, a temperature of freezing (0 Celsius) or below would indicate snow whereas a temperature above freezing would indicate rain.
850 mb height field The height field works very similar to the sea level pressure field. Lows and highs can found and compared to sea level locations. Strength of winds are again related to the packing of the height contours.
850 mb wind vector field The vector field shows wind direction and speed. Often this can be used to qualitatively show areas of convergence and divergence. In the middle and upper levels of the troposphere, this can be an indicator of existing upward (from divergence) or downward (from convergence) air motion. Upward motion is often linked to precipitation and downward to clear skies.